1,720,969 research outputs found
Broken-Symmetry Quantum Hall States in Twisted Bilayer Graphene
Full text linkTwisted bilayer graphene offers a unique bilayer two-dimensional-electron system where the layer separation is only in sub-nanometer scale. Unlike Bernal-stacked bilayer, the layer degree of freedom is disentangled from spin and valley, providing eight-fold degeneracy in the low energy states. We have investigated broken-symmetry quantum Hall (QH) states and their transitions due to the interplay of the relative strength of valley, spin and layer polarizations in twisted bilayer graphene. The energy gaps of the broken-symmetry QH states show an electron-hole asymmetric behaviour, and their dependence on the induced displacement field are opposite between even and odd filling factor states. These results strongly suggest that the QH states with broken valley and spin symmetries for individual layer become hybridized via interlayer tunnelling, and the hierarchy of the QH states is sensitive to both magnetic field and displacement field due to charge imbalance between layers. © The Author(s) 20161221sciescopu
Patternable large-scale molybdenium disulfide atomic layers grown by gold-assisted chemical vapor deposition
No full textA novel way to grow MoS2 on a large scale with uniformity and in desired patterns is developed.We use Au film as a catalyst on which [Mo(CO)6] vapor decomposes to form a Mo-Au surface alloy that is an ideal Mo reservoir for the growth of atomic layers of MoS2. Upon exposure to H2S, this surface alloy transforms into a few layers of MoS2, which can be isolated and transferred on an arbitrary substrate. By simply patterning Au catalyst film by conventional lithographic techniques, MoS2 atomic layers in desired patterns can be fabricated. © 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.149521sciescopu
Transfer-Free, Large-Scale Growth of High-Quality Graphene on Insulating Substrate by Physical Contact of Copper Foil
No full textHigh-quality, large-area, single-layer graphene was directly grown on top of a quartz substrate by a low-pressure chemical vapor deposition (CVD) process using Cu vapor as a catalyst. In this process, continuous generation and supply of highly concentrated Cu vapor is the key to the growth of largescale, high-quality graphene. It was achieved by direct physical contact, or "touch-down," of a Cu foil with an underlying sacrificial SiO2/Si substrate, and the target quartz substrate was placed on top of the Cu foil, eventually having a quartz/Cu/SiO2/Si sandwich structure. To establish the reaction mechanism, a test growth was performed without the quartz substrate, which revealed that Cu is diffused through the SiO2 layer of the sacrificial SiO2/Si substrate to form liquid-phase Cu-Si alloy that emits massive Cu vapor. This Cu vapor catalyzes thermal decomposition of supplied CH4 gas.11Nsciescopu
Synthesis and properties of molybdenum disulphide: from bulk to atomic layers
No full textMolybdenum disulphide (MoS2) has been one of the most interesting materials for scientists and engineers for a long time. While its bulk form has been in use in conventional industries as an intercalation agent and a dry lubricant for many years, its two-dimensional forms have attracted growing attention in recent years for applications in nano-electronic applications. Specifically, the single layer form of MoS2 shows significant potential as a semiconductor analogue of graphene. These exciting applications are spread over many fields, from flexible and transparent transistor devices, to low-power, high efficiency biological and chemical sensing applications. This Review Article, for the first time, provides a comprehensive overview of the synthesis, structural polytypes, properties, and applications of bulk, few layer, and single layer MoS2.open1110093sciescopu
Unique Crystallization of Fullerenes: Fullerene Flowers
Full text linkSolution-phase crystallization of fullerene molecules strongly depends on the types of solvent and their ratios because solvent molecules are easily included in the crystal lattice and distort its structure. The C-70 (solute)-mesitylene (solvent) system yields crystals with various morphologies and structures, such as cubes, tubes, and imperfect rods. Herein, using C-60 and C-70 dissolved in mesitylene, we present a novel way to grow unique flower-shaped crystals with six symmetric petals. The different solubility of C-60 and C-70 in mesitylene promotes nucleation of C-70 with sixfold symmetry in the early stage, which is followed by co-crystallization of both C-60 and C-70 molecules, leading to lateral petal growth. Based on the growth mechanism, we obtained more complex fullerene crystals, such as multi-deck flowers and tube-flower complexes, by changing the sequence and parameters of crystallization.1134Ysciescopu
Large-area two-dimensional bismuth selenide crystals synthesized by solution-based control of the nucleation environment
No full textTwo-dimensional (2D) Bi2Se3 is one of the most studied nanomaterials in recent years because of its fascinating electronic properties. However, previous synthesis methods, especially solution-based methods, were not capable of growing laterally large 2D Bi2Se3 crystals (mostly up to a few micrometers), and thus its real application and in-depth study was practically impossible. In this communication, we report a simple, reliable two-step method to synthesize large (20-50 mm in the lateral diameter and 10-15 nm in the thickness) disks of Bi2Se3 in the presence of ethylenediamine-tetraacetic acid (EDTA) and chloride ion, where EDTA acts as a complexing agent with bismuth(III). Depending on the growth conditions, we obtained 2D Bi2Se3 crystals having either a flat or spiral surface. We have thoroughly characterized the morphology, crystal structures, and electrical properties of these new disks, and we also discussed a possible growth mechanism based on the control over the surface chemistry and the nucleation stage.1122Ysciescopu
Improvement of work function and hole injection efficiency of graphene anode using CHF3 plasma treatment
No full textWereport improvement of hole injection efficiency of a graphene anode by tuning its work function
(WF) via surface fluorination.Weused chemical vapor deposition to synthesize high-quality graphene
sheets and then treated them withCHF3 plasma to induce fluorination.Weused x-ray photoelectron
spectroscopy to examine the fluorine coverage and the kind of chemical bonds in fluorinated
graphene (FG). Also, we used ultraviolet photoelectron spectroscopy to systematically study the changes
in theWFand sheet resistance of the FG sheets with varying plasma exposure time (0, 10, 30, 60,
90 s) to find an optimum fluorination condition for hole injection. TheWFof graphene sheets was
increased by up to 0.74 eV, as a result of the formation of carbon-fluorine bonds that function as
negative surface dipoles.Wefabricated hole-only devices and conducted dark injection space-chargelimited-
current transient measurement; the fluorination greatly increased the hole injection efficiency
of graphene anodes (from 0.237 to 0.652). The enhanced hole injection efficiency of FG anodes in our
study provides wide opportunities for applications in graphene-based flexible/stretchable organic
optoelectronics.©2015 IOP Publishing Ltd11sciescopu
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
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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