15 research outputs found
Selective synthesis of pure cobalt disulfide on reduced graphene oxide sheets and its high electrocatalytic activity for hydrogen evolution reaction
We synthesized single-phase CoS2 on a large scale by adding graphene oxide of sufficient quantity via the hydrothermal method using cobalt acetate and thioacetamide as precursors; this produced the hybrid of CoS2 with reduced graphene oxide which exhibited high electrocatalytic activity in the hydrogen evolution reaction.ope
Strain-Mediated Interlayer Coupling Effects on the Excitonic Behaviors in an Epitaxially Grown MoS2/WS2 van der Waals Heterobilayer.
van der Waals heterostructures composed of two different monolayer crystals have recently attracted attention as a powerful and versatile platform for studying fundamental physics, as well as having great potential in future functional devices because of the diversity in the band alignments and the unique interlayer coupling that occurs at the heterojunction interface. However, despite these attractive features, a fundamental understanding of the underlying physics accounting for the effect of interlayer coupling on the interactions between electrons, photons, and phonons in the stacked heterobilayer is still lacking. Here, we demonstrate a detailed analysis of the strain-dependent excitonic behavior of an epitaxially grown MoS2/WS2 vertical heterostructure under uniaxial tensile and compressive strain that enables the interlayer interactions to be modulated along with the electronic band structure. We find that the strain-modulated interlayer coupling directly affects the characteristic combined vibrational and excitonic properties of each monolayer in the heterobilayer. It is further revealed that the relative photoluminescence intensity ratio of WS2 to MoS2 in our heterobilayer increases monotonically with tensile strain and decreases with compressive strain. We attribute the strain-dependent emission behavior of the heterobilayer to the modulation of the band structure for each monolayer, which is dictated by the alterations in the band gap transitions. These findings present an important pathway toward designing heterostructures and flexible devices
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Department of Energy Engineering (Energy Engineering)clos
Evaluation of Water Quality Interaction by Dam and Weir Operation Using SWAT in the Nakdong River Basin of South Korea
Korean population-based external validation of western prognostic models for survival in metastatic renal cell cancer.
Does primary lesion have to be regarded as a target lesion when evaluating response in metastatic renal cell carcinoma (mRCC) treated with sunitinib?
Prevention of Transition Metal Dichalcogenide Photodegradation by Encapsulation with h-BN Layers
Transition metal dichalcogenides (TMDs) have recently received increasing attention because of their potential applications in semiconducting and optoelectronic devices exhibiting large optical absorptions in the visible range. However, some studies have reported that the grain boundaries of TMDs can be easily degraded by the presence of oxygen in water and by UV irradiation, ozone, and heating under ambient conditions. We herein demonstrate the photodegradation of WSe2 and MoSe2 by laser exposure (532 nm) and the subsequent prevention of this photodegradation by encapsulation with hexagonal boron nitride (h-BN) layers. The photodegradation was monitored by variation in peak intensities in the Raman and photoluminescence spectra. The rapid photodegradation of WSe2 under air occurred at a laser power of >0.5 mW and was not observed to any extent at <= 0.1 mW. However, in the presence of a water droplet, the photodegradation of WSe2 was accelerated and took place even at 0.1 mW. We examined the encapsulation of WSe2 with h-BN and found that this prevented photodegradation. However, a single layer of h-BN was not sufficient to fully prevent this photodegradation, and so a triple layer of h-BN was employed. We also demonstrated that the photodegradation of MoSe2 was prevented by encapsulation with h-BN layers. On the basis of X-ray photoelectron spectroscopy and scanning photoemission microscopy data, we determined that this degradation was caused by the photoinduced oxidation of TMDs. These results can be used to develop a general strategy for improving the stability of 2D materials in practical applications.close0
Work of breathing during SIMV with and without pressure support
Vertically stacked atomic layers from different layered crystals can be held
together by van der Waals forces, which can be used for building novel
heterostructures, offering a platform for developing a new generation of
atomically thin, transparent and flexible devices. The performance of these
devices is critically dependent on the layer thickness and the interlayer
electronic coupling, influencing the hybridisation of the electronic states as
well as charge and energy transfer between the layers. The electronic coupling
is affected by the relative orientation of the layers as well as by the
cleanliness of their interfaces. Here, we demonstrate an efficient method for
monitoring interlayer coupling in heterostructures made from transition metal
dichalcogenides using photoluminescence imaging in a bright-field optical
microscope. The colour and brightness in such images are used here to identify
mono- and few-layer crystals, and to track changes in the interlayer coupling
and the emergence of interlayer excitons after thermal annealing in
mechanically exfoliated flakes as well as a function of the twist angle in
atomic layers grown by chemical vapour deposition. Material and crystal
thickness sensitivity of the presented imaging technique makes it a powerful
tool for characterisation of van der Waals heterostructures assembled by a wide
variety of methods, using combinations of materials obtained through mechanical
or chemical exfoliation and crystal growth.Comment: 24 pages, 5 figure