1,720,964 research outputs found
Phase stability and Raman vibration of the molybdenum ditelluride (MoTe2) monolayer
No full textThe phase stability and phase transition of transition metal dichalcogenide (TMD) monolayer materials have attracted tremendous attention due to their attractive diverse potential applications. Here, firstprinciples calculations based on density-functional theory are carried out to study the newly synthesized MoTe2 monolayer. A phase different from the semiconducting trigonal prismatic structure and octahedral coordinated structure is found to be stable at room temperature in a free standing state, as evidenced by phonon spectrum analysis and molecular dynamic simulation. Raman vibrations of all the possible phases are calculated to provide additional information for the distinction of different phases in the experiment303011sciescopu
Vertically Conductive MoS2 Spiral Pyramid
No full textMoS2 spirals grown by the chemical vapor deposition method, driven by a threading dislocation, has a peculiar rhombohedral-like structure. This threading dislocation can carry helical current in the vertical direction and greatly enhances the vertical conductance in the MoS2 multilayer samples.
© 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim112131sciescopu
Unusually efficient photocurrent extraction in monolayer van der Waals heterostructure by tunnelling through discretized barriers
Full text linkTwo-dimensional layered transition-metal dichalcogenides have attracted considerable interest for their unique layer-number-dependent properties. In particular, vertical integration of these two-dimensional crystals to form van der Waals heterostructures can open up a new dimension for the design of functional electronic and optoelectronic devices. Here we report the layer-number-dependent photocurrent generation in graphene/MoS2/graphene heterostructures by creating a device with two distinct regions containing one-layer and seven-layer MoS2 to exclude other extrinsic factors. Photoresponse studies reveal that photoresponsivity in one-layer MoS2 is surprisingly higher than that in seven-layer MoS2 by seven times. Spectral-dependent studies further show that the internal quantum efficiency in one-layer MoS2 can reach a maximum of 65%, far higher than the 7% in seven-layer MoS2. Our theoretical modelling shows that asymmetric potential barriers in the top and bottom interfaces of the graphene/one-layer MoS2/graphene heterojunction enable asymmetric carrier tunnelling, to generate usually high photoresponsivity in one-layer MoS2 device. (c) The Author(s) 2016126281sciescopu
Confocal absorption spectral imaging of MoS2: Optical transitions depending on the atomic thickness of intrinsic and chemically doped MoS2
No full textWe performed a nanoscale confocal absorption spectral imaging to obtain the full absorption spectra
(over the range 1.5–3.2 eV) within regions having different numbers of layers and studied the variation of
optical transition depending on the atomic thickness of the MoS2 film. Three distinct absorption bands
corresponding to A and B excitons and a high-energy background (BG) peak at 2.84 eV displayed a
gradual redshift as the MoS2 film thickness increased from the monolayer, to the bilayer, to the bulk MoS2
and this shift was attributed to the reduction of the gap energy in the Brillouin zone at the K-point as the
atomic thickness increased. We also performed n-type chemical doping of MoS2 films using reduced
benzyl viologen (BV) and the confocal absorption spectra modified by the doping showed a strong
dependence on the atomic thickness: A and B exciton peaks were greatly quenched in the monolayer
MoS2 while much less effect was shown in larger thickness and the BG peak either showed very small
quenching for 1 L MoS2 or remained constant for larger thicknesses. Our results indicate that confocal
absorption spectral imaging can provide comprehensive information on optical transitions of microscopic
size intrinsic and doped two-dimensional layered materials.11411411sciescopu
Nanoreactor of Nickel-Containing Carbon-Shells as Oxygen Reduction Catalyst
No full textA Pt-free nanoreactor, consisting of N-doped hollow carbon nanocapsules with encapsulated Ni nanoparticles, is developed for high-performance oxygen reduction reaction (ORR) catalyst. The nanoreactor effect improves its catalytic activity for ORR mainly in a 4e(-) pathway. The presence of Ni nanoparticles within the nanoreactor significantly enhances the stability with a current retention of 90% after 40 h141611sciescopu
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
Large Work Function Modulation of Monolayer MoS2 by Ambient Gases
No full textAlthough two-dimensional monolayer transition-metal dichalcogenides reveal numerous unique features that are inaccessible in bulk materials, their intrinsic properties are often obscured by environmental effects. Among them, work function, which is the energy required to extract an electron from a material to vacuum, is one critical parameter in electronic/optoelectronic devices. Here, we report a large work function modulation in MoS2 via ambient gases. The work function was measured by an in situ Kelvin probe technique and further confirmed by ultraviolet photoemission spectroscopy and theoretical calculations. A measured work function of 4.04 eV in vacuum was converted to 4.47 eV with O2 exposure, which is comparable with a large variation in graphene. The homojunction diode by partially passivating a transistor reveals an ideal junction with an ideality factor of almost one and perfect electrical reversibility. The estimated depletion width obtained from photocurrent mapping was ∼200 nm, which is much narrower than bulk semiconductors. © 2016 American Chemical Society127311sciescopu
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
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