1,721,065 research outputs found
Single-molecule light emission at room temperature on a wide-band-gap semiconductor
Full text linkRoom-temperature light emission from single chemisorbed perylene based molecules adsorbed on silicon
carbide (SiC) is probed by scanning tunnelingmicroscopy (STM).Anewapproach to STM-induced luminescence
of a single molecule is explored using a wide-band-gap semiconductor to decouple electronically the molecule
from the surface. After molecular adsorption, the lowest unoccupied molecular orbital and the highest occupied
molecular orbital (HOMO) both lie within the bulk band gap and below the Fermi level of the substrate. The
maximum photon energy of the light emission from the molecule shows a fixed shift of 1.5 eV relative to the
maximum energy of the tunnel electrons. This is consistent with the photons being generated by inelastic electron
tunneling between the HOMO and the unoccupied electronic states of the STM tip.1661sciescopu
Protecting nickel with graphene spin-filtering membranes: A single layer is enough
Full text linkWe report on the demonstration of ferromagnetic spin injectors for spintronics which are protected against oxidation through passivation by a single layer of graphene. The graphene monolayer is directly grown by catalytic chemical vapor deposition on pre-patterned nickel electrodes. X-ray photoelectron spectroscopy reveals that even with its monoatomic thickness, monolayer graphene still efficiently protects spin sources against oxidation in ambient air. The resulting single layer passivated electrodes are integrated into spin valves and demonstrated to act as spin polarizers. Strikingly, the atom-thick graphene layer is shown to be sufficient to induce a characteristic spin filtering effect evidenced through the sign reversal of the measured magnetoresistance. © 2015 Author(s)126271sciescopu
Sub-nanometer Atomic Layer Deposition for Spintronics in Magnetic Tunnel Junctions Based on Graphene Spin-Filtering Membranes
No full textWe report on the successful integration of low-cost, conformal, and versatile
atomic layer deposited (ALD) dielectric in NiAl2O3Co magnetic tunnel junctions (MTJs)
where the Ni is coated with a spin-filtering graphene membrane. The ALD tunnel barriers, as
thin as 0.6 nm, are grown layer-by-layer in a simple, low-vacuum, ozone-based process, which
yields high-quality electron-transport barriers as revealed by tunneling characterization. Even
under these relaxed conditions, including air exposure of the interfaces, a significant tunnel
magnetoresistance is measured highlighting the robustness of the process. The spin-filtering
effect of graphene is enhanced, leading to an almost fully inversed spin polarization for the Ni
electrode of42%. This unlocks the potential of ALD for spintronics with conformal, layer-by-layer control of tunnel barriers in magnetic tunnel junctions
toward low-cost fabrication and down-scaling of tunnel resistances.495111sciescopu
Fluorescence Lifetime and Blinking of Individual Semiconductor Nanocrystals on Graphene
No full textA new class of optoelectronic nanodevices
consisting of 0D semiconductor nanocrystals and 2D single
graphene layers is attracting much attention. In particular, such a
system may be used to investigate and control the transfer of
energy and charge in low-dimensional systems. To this end, the
fluorescence dynamics of individual colloidal quantum dots
(QDs) on graphene are investigated on both the 10−9−10−8 s
time scale (fluorescence lifetime) and the 100−102 s time scale
(blinking statistics) in this paper. We find that (i) a nonradiative
energy transfer rate of ≈5 × 108 s−1 is obtained from the reduced lifetimes of QDs on graphene as opposed to those on insulating
substrates such as glass; (ii) QDs still exhibit fluorescence intermittency (“blinking”) on graphene; (iii) the cumulative
distribution functions of the “off” times may be described by power-law statistics; (iv) QD coupling to graphene increases the
time spent in the “on” state while the time spent in the “off” state remains relatively unchanged; and (v) the fluorescence
emission spectrum of the QDs is practically unaltered by the QD−graphene coupling.1991sciescopu
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
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Schottky-barrier quantum well in two-dimensional semiconductor nanotransistors
No full textTwo-dimensional (2D) semiconductors are promising candidates for quantum-well devices with the inherent quantum confinement of the subnanometer thickness along the out-of- plane direction. Coulomb/quantum oscillation phenomena have been demonstrated in 2D semiconductors devices, including artificial quantum dots with local electrostatic gating and stacked heterostructure quantum wells. However, the exact quantized energy states, let alone the complexity of the device structures and low observation temperature, have not been clearly revealed. Here, we report a rational fabrication platform of 2D semiconductor nanotransistors to directly construct a Schottky-barrier quantum well (SBQW) for quantized energy states engineering. The feature size of the quantum well is tailored by a vertical nanochannel of monolayer transition metal dichalcogenides (TMDCs) via an insulating spacer. Meanwhile, the potential barrier is constructed by the Schottky barrier. Quantum oscillations are clearly observed and the quantized energy states are extracted from the source-drain current modulated with the gate bias. Such quantum oscillations are preserved up to similar to 100 K with a channel length of approximately 16 nm. With an evaluated Schottky barrier height of approximately 27 meV, the quantized energy states are estimated from 2 to 24 meV near the conduction band edge, consistent with corresponding explicit principal quantum numbers. Our work demonstrates the feasibility of moving 2D van der Waals semiconductor nanotransistors towards quantum transistors. (c) 2020 Elsevier Ltd. All rights reserved.11Nsciescopu
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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