Showing papers by "Songyou Wang published in 2020"
TL;DR: This work provides a facile way to fabricate high capacity electrodes in LIBs/SIBs, which is also instructive for the design of other heteroatomic doped electrodes and imine-N is demonstrated to be the ideal doping format to enhance the Li/Na storage performance.
Abstract: High energy density is the major demand for next-generation rechargeable batteries, while the intrinsic low alkali metal adsorption of traditional carbon-based electrode remains the main challenge. Here, the mechanochemical route is proposed to prepare nitrogen doped γ-graphyne (NGY) and its high capacity is demonstrated in lithium (LIBs)/sodium (SIBs) ion batteries. The sample delivers large reversible Li (1037 mAh g-1 ) and Na (570.4 mAh g-1 ) storage capacities at 100 mA g-1 and presents excellent rate capabilities (526 mAh g-1 for LIBs and 180.2 mAh g-1 for SIBs) at 5 A g-1 . The superior Li/Na storage mechanisms of NGY are revealed by its 2D morphology evolution, quantitative kinetics, and theoretical calculations. The effects on the diffusion barriers (Eb ) and adsorption energies (Ead ) of Li/Na atoms in NGY are also studied and imine-N is demonstrated to be the ideal doping format to enhance the Li/Na storage performance. Besides, the Li/Na adsorption routes in NGY are optimized according to the experimental and the first-principles calculation results. This work provides a facile way to fabricate high capacity electrodes in LIBs/SIBs, which is also instructive for the design of other heteroatomic doped electrodes.
36 citations
TL;DR: The optical properties of chemical vapor deposition-grown PtSe2 thin films with varied thicknesses via spectroscopic ellipsometry are explored and the resonant energies, extracted from the Lorentz model, to different interband electronic transitions between valence bands and conduction bands in the Brillouin zone are ascribed.
Abstract: Platinum diselenide (PtSe2) has attracted huge attention due to its intriguing physical properties for both fundamental research and promising applications in electronics and optoelectronics. Here, we explored the optical properties of chemical vapor deposition-grown PtSe2 thin films with varied thicknesses via spectroscopic ellipsometry. The dielectric function was extracted by using a Lorentz model over the spectral range of 1.25-6.0 eV. We firstly ascribed the resonant energies, extracted from the Lorentz model, to different interband electronic transitions between valence bands and conduction bands in the Brillouin zone. A predicted exciton is observed at 2.18 eV for the monolayer and the corresponding exciton binding energy is 0.65 eV, in line with previous theoretical calculation and the measured absorption spectra. Additionally, the exciton peak shows a red shift with the increase of thickness, which is the consequence of strong interlayer interaction. These results enrich the fundamental understanding of PtSe2 and are conducive to its potential applications.
16 citations
TL;DR: In this paper, the origin of multi-level resistance states in K2Sb8Se13 has been investigated through ab initio simulations, and it was shown that adding electronic holes were largely responsible for the decrease in resistance.
Abstract: Phase change memory is an excellent candidate for next-generation memory technologies with a high operation speed, but the memory capacity is not very satisfactory, due to which engineers have to add the 3D stacking technology (3D XPoint) for new products. Alternatively, multi-level storage is an easy approach to enable large data density and probably future neuromorphic computing. Lately, K2Sb8Se13 has attracted considerable attention as a multi-level phase change material because it exhibits an interesting amorphous-to-amorphous (polyamorphic) transformation before crystallization, and these two polyamorphic states as well as the crystalline phase show distinct resistances, adding a new data state to the existing “0” and “1”. Understanding and stabilizing this new amorphous state is the key to the application of this material; here, we have investigated these two amorphous states through ab initio simulations. We found that these two states showed obvious differences in the local structures, and the void concentration revealed by the low-electron-density areas indicated stronger interactions between the atomic clusters in the denser phase. The density of states and electron localization function were analyzed and we confirmed that adding electronic holes were largely responsible for the decrease in resistance. In this work, we have discovered the origin of multi-level resistance states in K2Sb8Se13, paving the way for the design of new phase change memory devices based on this material.
13 citations
TL;DR: In this paper, the effects of quantum confinement on the excitonic property and electronic band structures of centimeter-scale MoS2 films (number of layers: N = 1, 2, 4, and 18) through spectroscopic ellipsometry were investigated.
12 citations
16 Jul 2020
TL;DR: Electronic properties of monolayer tellurium with three proposed atomic configurations under external electric field were investigated through first-principles calculations and demonstrate that α-Te and γ-Te have indirect band gaps, whereas β-Te, when no electric field is applied, can be considered as a direct semiconductor.
Abstract: Electronic properties of monolayer tellurium (Te) with three proposed atomic configurations under external electric field were investigated through first-principles calculations. The calculated results demonstrate that α-Te and γ-Te have indirect band gaps, whereas β-Te, when no electric field is applied, can be considered as a direct semiconductor. An interesting structural change occurs in α- and γ-phase Te under a specific electric field strength, as does a change in structural chirality. In the presence of a perpendicular electric field, the band gaps can be modified and drawn close to 0 eV at a certain critical electric field strength. Before that, the band gaps of α-Te and γ-Te are nearly constant, while that of β-Te shows a quadratic relationship to electric field strength. These findings not only enrich our understanding of the electronic properties of monolayer tellurium but also show that monolayer tellurium has tremendous potential in nanoscale electronic devices owing to its tunable band gaps.
11 citations
TL;DR: An open-access database for magnetic compounds, as well as for magnetic clusters, with a focus on magnets free from rare earths is developed in this paper, where data-intensive methods are used to facilitate the theoretical and experimental design and discovery of new magnetic materials.
Abstract: An open-access database specialized for magnetic compounds, as well as for magnetic clusters, is developed with a focus on magnets free from rare earths. Data-intensive methods are used to facilitate the theoretical and experimental design and discovery of new magnetic materials. The utility of the datasets for computational screening, machine-learning modeling, and experimental fabrication is discussed.
11 citations
TL;DR: The findings provide a deep insight into the origin of local structural order in supercooled liquid Ge3Sb2Te6, which is of great importance for the comprehensive understanding of amorphization and crystallization processes.
Abstract: Phase-change materials such as Ge–Sb–Te compounds have attracted much attention due to their potential value in electrical data storage. In contrast to the amorphous and crystalline phases, supercooled liquids are far from being deeply understood despite their inevitable role in both amorphization and crystallization processes. To this end, we have studied the dynamics properties and structural characteristics of liquid and supercooled liquid Ge3Sb2Te6 during the fast cooling process. As the temperature decreases, chemical bonds become more homogeneous, but coordination numbers of Ge, Sb and Te atoms change very little. Meanwhile, the structural order of short-range configuration is obviously enhanced. Further studies suggest that Ge-centered, Sb-centered and Te-centered configurations change to the more ordered defective octahedrons mainly by adjusting the bond-angle relationship and bond length, rather than just by changing the coordination environment. It is the more ordered octahedrons that promote the formation of medium-range order. Our findings provide a deep insight into the origin of local structural order in supercooled liquid Ge3Sb2Te6, which is of great importance for the comprehensive understanding of amorphization and crystallization processes.
5 citations
TL;DR: In this paper, electron beam evaporation and spectroscopic ellipsometry were combined with X-ray diffraction and field emission for the characterization of Ag films with different nanostructures.
Abstract: Silver (Ag) films with different nanostructures were prepared by electron beam evaporation and characterized by spectroscopic ellipsometry in combination with X-ray diffraction and field emission s...
3 citations
TL;DR: In this article, the thickness-dependent optical properties of YF3 ultrathin films in the 300−820 nm wavelength range were studied using Spectroscopic ellipsometry.
Abstract: Yttrium fluoride (YF3) thin films with a thickness range of 10.8−1079.0 nm were prepared by electron beam evaporation. Spectroscopic ellipsometry was used to study the thickness-dependent optical properties of YF3 ultrathin films in the 300−820 nm wavelength range. With increasing thicknesses, the refractive indices of the intrinsic YF3 films increase slightly and approach that of bulk YF3 due to the decrease of void fractions. The effective refractive indices of the YF3 films also increase with increasing thicknesses, due to the surface and interface effects besides the contribution of decrease of void fractions.
2 citations
28 Jun 2020
TL;DR: In this article, a simple method to improve the thermoelectric performance of the RF sputtered bismuth telluride films by raising the power of deposition was presented.
Abstract: In this work, we present a simple method to improve the thermoelectric performance of the RF sputtered bismuth telluride films by raising the power of deposition The as-deposited samples synthesized under different powers were investigated and compared It shows that the films prepared under relatively higher power conditions exhibit much higher electrical conductivity to result in a greater power factor accompanied with a minor drop in the Seebeck coefficients A relationship is established between the improvement in thermoelectric performance and the decrease in crystallinity, which might also reduce the thermal conductivity A maximum power factor of 565 × 10−4 W·m−1·K−2 at 470 K is obtained for the sample deposited under 50 W with its Seebeck coefficient being −105 μV/K The temperature-dependent behaviors of the samples are also looked into and discussed This work might offer an in-situ and cost-effective approach to improve the performance of thermoelectric materials
2 citations
TL;DR: The differences of principal refractive indices were affected by both the deposition angle and the volume fraction of YF3, which is attributed to the self-shadowing effect and limited adatom diffusion.
Abstract: Yttrium fluoride (YF3) columnar thin films (CTFs) were fabricated by electron beam evaporation with the glancing angle deposition method. The microstructures and optical properties of YF3 CTFs were studied systematically. The YF3 films grown at different deposition angles are all amorphous. As the deposition angle increases, the columns in YF3 CTFs become increasingly separated and inclined, and the volume fraction of YF3 decreases, resulting in lower refractive indices. This phenomenon is attributed to the self-shadowing effect and limited adatom diffusion. The YF3 CTFs are optically biaxial anisotropic with the long axis (c-axis) parallel to the columns, the short axis (b-axis) perpendicular to the columns, and the other axis (a-axis) parallel to the film interface. The principal refractive index along the b-axis for the 82°-deposited sample is approximately 1.233 at 550 nm. For the 78°-deposited sample, the differences of principal refractive indices between the c-axis and the b-axis and between the a-axis and the b-axis reach the maximum 0.056 and 0.029, respectively. The differences of principal refractive indices were affected by both the deposition angle and the volume fraction of YF3.
Patent•
27 Mar 2020
TL;DR: In this paper, a coma-eliminating broadband high-resolution spectrometer consisting of an entrance slit, a collimating mirror, an integrated grating, a two-dimensional focusing imaging mirror, and a 2-dimensional area array detector was proposed.
Abstract: The coma-eliminating broadband high-resolution spectrometer comprises an entrance slit, a collimating mirror, an integrated grating, a two-dimensional focusing imaging mirror and a two-dimensional area array detector; incident light enters along the entrance slit, and penetrates a light through hole in the center of an integrated grating; and the incident light enters the collimating reflector; the incident light enters the integrated grating along the coaxial light path L1 after being collimated by the collimating mirror, and is focused by the two-dimensional focusing imaging mirror after being diffracted by each sub-grating of the integrated grating, diffracted light in a full spectral region enters a focal plane of the two-dimensional area array detector along the coaxial light path L2for detection, and off-axis angles of L1 and L2 light paths are zero According to the invention, no mechanical displacement part is used, wide-spectrum high-resolution high-speed detection and analysis for completely eliminating coma influence difference in the diffraction direction in a full-spectrum region are realized, and the spectral resolution and the working reliability are very high
Patent•
27 Mar 2020
TL;DR: In this paper, a multichannel broadband high-resolution spectrograph, comprising a plurality of light source incident slits, integrated grating, shared two-dimensional focus imaging mirror, and a 2D area array detector, is presented.
Abstract: The present invention discloses a multichannel broadband high-resolution spectrograph, comprising a plurality of light source incident slits, a multichannel integrated grating, a multichannel shared two-dimensional focus imaging mirror and a two-dimensional area array detector which are sequentially disposed along a light source incident or reflection line, wherein the multichannel integrated grating consists of a plurality of sub-gratings, incident light enters the corresponding integrated gratings along the light source incident slits and then is focused by the shared two-dimensional focus imaging mirror after diffraction of the integrated grating, and diffraction light in a full-spectrum region is incident onto a focal plane of the two-dimensional area array detector for detection. No any mechanical displacement part is disposed, multichannel, full-spectrum and high-speed detection and analysis is achieved, and the present disclosure has high spectrum resolution and working reliability.
TL;DR: In this paper, the melting and deflagration of indium particle thin films with an average diameter of 43.2 nm were characterized by temperature-dependent ellipsometry, and during ellipsometric measurement,...
Abstract: The melting and deflagration of nanometer indium particle thin films with an average diameter of 43.2 nm were characterized by temperature-dependent ellipsometry. During ellipsometric measurement, ...