12067-46-8Relevant articles and documents
Effect of Long-Range and Local Order of Exfoliated and Proton-Beam-irradiated WSe2 Nanosheets for Sodium Ion Battery Application
Chun, Yu-Gyeong,Lee, Won-Jae,Lee, Minseop,Paek, Seung-Min
, p. 665 - 670 (2018)
WSe2 nanosheets were synthesized by mechanical exfoliation via sonication of bulk WSe2 in organic solvent. The exfoliated WSe2 nanosheets were separated into two different particle size ranges, and were then irradiated by
Morphological characteristics in polycrystalline tungsten diselenide regulating transport properties lead to predominant thermoelectric performance
Kim, Cham,Baek, Ju Young,Kim, Dong Hwan,Kim, Jong Tae,Lopez, David Humberto,Kim, Taewook,Kim, Hoyoung
, p. 183 - 189 (2017)
We studied a polycrystalline p-type WSe2 semiconductor for thermoelectric applications. The polycrystalline WSe2 nanocompound was prepared via a thermal reaction process of tungsten and selenium elements and it was sintered to produce a bulk structure using spark plasma sintering equipment. The resulting bulk specimen showed different morphological aspects, in which we observed irregularly-shaped grains along the direction perpendicular to the sintering pressing direction (i.e., along transversal direction) while finding thin layers along the parallel direction (i.e., along longitudinal direction). The specimen recorded a significantly low longitudinal thermal conductivity possibly because longitudinal phonon transport should be hindered due to the thin layers. Electron transport along the longitudinal direction might not be greatly interrupted by the morphological characteristics because the specimen recorded high carrier mobility along the direction resulting in lower electrical resistivity than that of a single crystalline equivalent. The specimen also showed moderate carrier concentration, which led to a plausible Seebeck coefficient. Since the specimen exhibited the significantly low thermal conductivity with the electrical properties, it recorded a higher figure of merit than the equivalent, which is the highest thermoelectric performance for p-type WSe2 in bulk phase ever developed.
In-plane thermal conductivity of disordered layered W Se2 and (W)x (W Se2) y superlattice films
Mavrokefalos, Anastassios,Nguyen, Ngoc T.,Pettes, Michael T.,Johnson, David C.,Shi, Li
, (2007)
It was recently reported that misoriented layered W Se2 and (W)x (W Se2) y films possess extremely low cross-plane thermal conductivity. Here, we report that the in-plane thermal conductivity results for W Se2 and W4 (W Se2) 10 films measured by using a suspended device are about 30 times higher than the cross-plane values because of the in-plane ordered and cross-plane disordered structures and about six times lower than that of compacted single-crystal W Se2 platelets. The additional W layers in the W4 (W Se2) 10 films were found to greatly increase the in-plane electrical conductivity relative to the W Se2 films, but reduce the in-plane lattice thermal conductivity assuming the Wiedemann-Franz law.
Synthesis, crystal structure and physical properties of a novel quaternary selenide Cu6GeWSe8
Chen, Genfu,Gu, Yadong,Ren, Zhian,Ruan, Binbin,Yang, Qingsong,Zhou, Menghu
, (2021)
Here we report a novel quaternary selenide Cu6GeWSe8 synthesized directly from the constituent elements, which forms within the temperature range from 460 to 620 ?°C. It crystallizes in the space group P63mc with two formula units in the cell of dimensions a ?= ?7.8651 (5) ?, c ?= ?12.9275 (6) ?. In the unit cell composed of MSe4 (M ?= ?Cu, Ge and W) tetrahedrons, Cu atoms occupy two sets of 6c Wyckoff positions, Ge and W atoms respectively occupy 2a and 2b positions, while Se atoms are located at four inequivalent sites, respectively 2b (Se1), 6c (Se2), 6c (Se3) and 2a (Se4). The electrical resistivity and Vis-Nir absorption spectrum indicate that the compound exhibits a semiconducting behavior with an optical band gap of 1.586 ?eV Cu6GeWSe8 shows diamagnetism at room temperature and the emergence of a Curie-Weiss-like tail at low temperature. The band structure calculation demonstrates that the title compound has a direct band gap, and Cu and Se atoms dominantly contribute to the energy bands and density of states. Cu is mostly in 3d10 state (+1 valence) and Se in 4p6 state (?2 valence). On the basis of the experimental and calculation results, it is concluded that Cu6GeWSe8 is a diamagnetic direct-gap semiconductor.
Solution-phase synthesis of highly conductive tungsten diselenide nanosheets
Antunez, Priscilla D.,Webber, David H.,Brutchey, Richard L.
, p. 2385 - 2387 (2013)
A high-yielding synthesis of colloidal 2H-WSe2 (tungsten diselenide) nanosheets was reported, which were shown to be phase pure by x-ray diffraction (XRD). The synthesis of WSe2 nanosheets was achieved by the injection of 185 μL ditert-butyl diselenide (tBu2Se2) into a solution of 150 mg WCl4 in 25 mL of dodecylamine at 150°C under nitrogen. The solution was then heated to 225°C and held at this temperature for 6 h prior to quenching. Tetra-noctylammonium bromide (TOAB) was added during the workup to prevent agglomeration of the nanosheets. The final washed product was highly dispersible in tetramethylurea (TMU) and 1,2-dichlorobenzene, forming colloidal suspensions that were stable over the course of several months. Preferential sheet alignment along the direction upon solution casting was reflected in the XRD pattern and the correspondingly high conductivity values of the resulting thin films.
Standard molar enthalpy of formation by fluorine-combustion calorimetry of tungsten diselenide (WSe2). Thermodynamics of the high-temperature vaporization of WSe2. Revised value of the standard molar enthalpy of formation of molybdenite (MoS2)
O'Hare, P. A. G.,Lewis, Brett M.,Parkinson, B. A.
, p. 681 - 692 (1988)
A high-purity sample of WSe2, containing in total mass fraction less than 1 x 10-4 of oxygen and other impurities, has been synthesized by combination of the elements.The standard specific energy of combustion of pure WSe2 in fluorine, as measured by high-precision calorimetry, is -(10993.7+/-15.0) J*g-1, and the derived standard molar enthalpy of formation ΔfHm0 is -(185.3+/-5.5) kJ*mol-1 at T = 298.15 K and p0 = 0.101325 MPa.This result is compared with other literature values, and the equilibrium partial pressures of Se2(g) and Se(g) are estimated for decomposition of WSe2 to and 1/2WSe2 to .Our published result (J.Chem.Thermodynamics 1970, 2, 797) for ΔfHm0(MoS2) at 298.15 K has been revised to -(271.8+/-4.9) kJ*mol-1.
Novel magnetically separable Fe3O4-WSe2/NG photocatalysts: Synthesis and photocatalytic performance under visible-light irradiation
An, Baihong,Liu, Yanan,Xu, Chengcheng,Wang, Han,Wan, Jun
, p. 8914 - 8923 (2018)
Visible light responsive Fe3O4-WSe2/NG (nitrogen doped graphene oxide) heterojunction nanocomposites were synthesized by a hydrothermal synthesis route, in which Fe3O4 and WSe2 particles were coated on the surface of NG. The samples were characterized by XRD, SEM, TEM, XPS, VSM, UV-vis DRS, TOC, and GC-MS techniques. The results showed that the photocatalytic activity of Fe3O4-WSe2/NG photocatalysts under visible-light illumination was higher than that of WSe2/NG owing to the narrow band gap energy and delayed electron-hole recombination, and Fe3O4 can be used in advanced oxidation processes (AOPs) to degrade organic pollutants at pH 3 and 3.0 mM H2O2. Moreover, the mass fraction of Fe3O4 had a great effect on the photocatalytic activity of Fe3O4-WSe2/NG. Among the hybrid photocatalysts, 30 wt%Fe3O4-WSe2/NG (30 wt% of Fe3O4) exhibited the highest photocatalytic activity with a rate constant of 0.05589 min-1 for the degradation of MB in aqueous solution under visible light irradiation, and the removal efficiency reached 98.8% which was 1.6 times higher than that of WSe2/NG. More importantly, the magnetic properties of 30 wt%Fe3O4-WSe2/NG were analyzed and its reusability was also investigated after four successive runs by applying an external magnetic field.
Low-Temperature Solution Synthesis of Transition Metal Dichalcogenide Alloys with Tunable Optical Properties
Sun, Yifan,Fujisawa, Kazunori,Lin, Zhong,Lei, Yu,Mondschein, Jared S.,Terrones, Mauricio,Schaak, Raymond E.
, p. 11096 - 11105 (2017)
Nanostructures of layered transition metal dichalcogenide (TMD) alloys with tunable compositions are promising candidates for a broad scope of applications in electronics, optoelectronics, topological devices, and catalysis. Most TMD alloy nanostructures are synthesized as films on substrates using gas-phase methods at high temperatures. However, lower temperature solution routes present an attractive alternative with the potential for larger-scale, higher-yield syntheses of freestanding, higher surface area materials. Here, we report the direct solution synthesis of colloidal few-layer TMD alloys, MoxW1-xSe2 and WS2ySe2(1-y), exhibiting fully tunable metal and chalcogen compositions that span the MoSe2-WSe2 and WS2-WSe2 solid solutions, respectively. Chemical guidelines for achieving the targeted compounds are presented, along with comprehensive structural characterizations (X-ray diffraction, electron microscopy, Raman, and UV-visible spectroscopies). High-resolution microscopic imaging confirms the formation of TMD alloys and identifies a random distribution of the alloyed elements. Analysis of the tilt-angle dependency of the intensities associated with atomic-resolution annular dark field imaging line scans reveals the types of point vacancies present in the samples, thus providing atomic-level insights into the structures of colloidal TMD alloy nanostructures that were previously only accessible for substrate-confined films. The A excitonic transition of the TMD alloy nanostructures can be readily adjusted between 1.51 and 1.93 eV through metal and chalcogen alloying, correlating the compositional modulation to the realization of tunable optical properties.
Electronic energy states of tungsten dichalcogenides by low energy electron loss spectroscopy study
Ito, Toshimichi,Iwami, Motohiro,Hiraki, Akio
, p. 106 - 113 (1981)
Low energy electron loss spectroscopy (ELS) was performed on tungsten dichalcogenides (WS2 and WSe2) by using incident electron energies of 30-360 eV. The ELS spectra in the second derivative form had considerable structures. Maxima
Observation of superconductivity in pressurized 2M WSe2 crystals
Fang, Yuqiang,Dong, Qing,Pan, Jie,Liu, Hanyu,Liu, Pan,Sun, Yiyang,Li, Quanjun,Zhao, Wei,Liu, Bingbing,Huang, Fuqiang
, p. 8551 - 8555 (2019)
In this communication, we report a new-phase 2M WSe2 with a monoclinic space group C2/m. 2M WSe2 presents a metallic behavior under ambient pressure and shows a superconducting transition with a maximum Tc of 7.3 K at 10.7 GPa, which arises from the enhanced density of states near the Fermi surface upon pressurization.
