22 research outputs found
Topology hierarchy of transition metal dichalcogenides built from quantum spin Hall layers
The evolution of the physical properties of two-dimensional material from
monolayer limit to the bulk reveals unique consequences from dimension
confinement and provides a distinct tuning knob for applications. Monolayer
1T'-phase transition metal dichalcogenides (1T'-TMDs) with ubiquitous quantum
spin Hall (QSH) states are ideal two-dimensional building blocks of various
three-dimensional topological phases. However, the stacking geometry was
previously limited to the bulk 1T'-WTe2 type. Here, we introduce the novel
2M-TMDs consisting of translationally stacked 1T'-monolayers as promising
material platforms with tunable inverted bandgaps and interlayer coupling. By
performing advanced polarization-dependent angle-resolved photoemission
spectroscopy as well as first-principles calculations on the electronic
structure of 2M-TMDs, we revealed a topology hierarchy: 2M-WSe2, MoS2, and
MoSe2 are weak topological insulators (WTIs), whereas 2M-WS2 is a strong
topological insulator (STI). Further demonstration of topological phase
transitions by tunning interlayer distance indicates that band inversion
amplitude and interlayer coupling jointly determine different topological
states in 2M-TMDs. We propose that 2M-TMDs are parent compounds of various
exotic phases including topological superconductors and promise great
application potentials in quantum electronics due to their flexibility in
patterning with two-dimensional materials
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Fast Li-ion battery chemistry enabled by small-sized solvent
Carbonate-based electrolytes, known for their high solvation energy and high ionic conductivity at room temperature, present significant challenges in ultra-low temperature and fast charging applications. In the February issue of
Nature
, Fan and colleagues demonstrated that utilizing solvents like fluoroacetonitrile with small molecular size and low solvation energy, facilitates the creation of rapid ion-conduction ligand channels and enables the formation of an inorganic-rich interphase for high-performance ionic batteries, effectively addressing the aforementioned challenges
Rectification magnetoresistance device: Experimental realization and theoretical simulation
A unique technique has been proposed to realize rectification magnetoresistance (RMR) by combining a commercial diode and a magnetoresistance component in parallel. The observed RMR could be greatly tuned in a wide range by applying direct current and alternating current simultaneously to the device. Moreover, a quantitative theoretical model has been established, which well explained both the observed RMR and the electrical manipulation behavior. The highly tunable RMR and the correlated magnetoelectric functionalities provide an alternative route for developing multi-functional spintronics devices
Sparse kernel entropy component analysis for dimensionality reduction of biomedical data
Dimensionality reduction is ubiquitous in biomedical applications. A newly proposed spectral dimensionality reduction method, named kernel entropy component analysis (KECA), can reveal the structure related to Renyi entropy of an input space data set. However, each principal component in the Hilbert space depends on all training samples in KECA, causing degraded performance. To overcome this drawback, a sparse KECA (SKECA) algorithm based on a recursive divide-and-conquer (DC) method is proposed in this work. The original large and complex problem of KECA is decomposed into a series of small and simple sub-problems, and then they are solved recursively. The performance of SKECA is evaluated on four biomedical datasets, and compared with KECA, principal component analysis (PCA), kernel PCA (KPCA), sparse PCA and sparse KPCA. Experimental results indicate that the SKECA outperforms conventional dimensionality reduction algorithms, even for high order dimensional features. It suggests that SKECA is potentially applicable to biomedical data processing. (C) 2015 Elsevier B.V. All rights reserved
Influences of Powder Source Porosity on Mass Transport during AlN Crystal Growth Using Physical Vapor Transport Method
We developed a two-dimensional (2D) transport model to investigate mass transport during bulk AlN crystal growth via the physical vapor transport (PVT) process using the finite element method (FEM), taking the powder source porosity, buoyancy, and vapor diffusion into account. The porosity effects of the powder source on mass transport under various growth conditions were investigated in detail. The simulation results show that the porosity of the powder source significantly affects the mass transport process during AlN sublimation growth. When the porosity of the powder source decreases, the growth rate becomes more uniform along the seed deposition surface, although the sublimation rate and crystal growth rate decrease, which can be attributed to the reduced specific surface area of the powder source and the reduced flow rate of Al vapor in the powder source. A flat growth interface can be achieved at a porosity of 0.2 under our specific growth conditions, which in turn facilitate the growth of high-quality AlN crystals and better yield. The decomposition of the powder source and the transport of Al vapor in the growth chamber can be suppressed by increasing the pressure. In addition, the AlN growth rate variation along the deposition surface can be attributed to the Al vapor pressure gradient caused by the temperature difference in the growth chamber
A Hydrothermal Synthesis Process of ZSM-5 Zeolite for VOCs Adsorption Using Desilication Solution
ZSM-5 zeolite is a kind of high-value-added porous aluminosilicate zeolite. The use of the coal gasification slag utilization process by-product desilication liquid as a silicon raw material to replace the current raw materials such as water glass will help reduce production costs and achieve high-value utilization of solid waste. ZSM-5 zeolites for volatile organic compounds (VOCs) adsorption were prepared by a one-step hydrothermal method using the desilication solution prepared from coal gasification slag as the main silicon source and sodium source. The effects of crystallization reaction time, the crystallization temperature, the Na2O/SiO2 molar ratio, and the SiO2/Al2O3 molar ratio on the relative crystallinity and the specific surface area of the ZSM-5 zeolite were investigated and optimized. The optical reaction conditions were as follows: a crystallization time of 12 h, a crystallization temperature of 170 °C, a Na2O/SiO2 molar ratio of 0.2, and a SiO2/Al2O3 molar ratio of 200. The optimal ZSM-5 zeolite synthesized is hexagonal, with regular grains, a relative crystallinity of 101.48%, a specific surface area of 337.48 m2·g−1, and a pore volume of 0.190 cm3·g−1. And the optimal ZSM-5 zeolite was composed of SiO2 content of 97.52 wt%, Al2O3 content of 1.58 wt%, Na2O content of 0.33 wt%, and SiO2/Al2O3 molar ratio of 104.93. Na2O/SiO2 molar ratio is 0.0033. The results of static adsorption experiments show that the static adsorption capacities of ZSM-5 zeolite for p-xylene, benzene, toluene, and butyl acetate were 118.85, 69.98, 68.74, and 95.85 mg·g−1, respectively, which can effectively adsorb VOCs. The synthetic process of the ZSM-5 zeolite is a simple preparation process and short in synthesis time. The results of this study not only help to realize the high-value utilization of silicon components in solid waste, but also provide an economical and effective way to synthesize VOCs adsorption materials