- Effect of Long-Range and Local Order of Exfoliated and Proton-Beam-irradiated WSe2 Nanosheets for Sodium Ion Battery Application
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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
- Chun, Yu-Gyeong,Lee, Won-Jae,Lee, Minseop,Paek, Seung-Min
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- Site Selective Doping of Ultrathin Metal Dichalcogenides by Laser-Assisted Reaction
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Laser-assisted phosphorus doping is demonstrated on ultrathin transition-metal dichalcogenides (TMDCs) including n-type MoS2 and p-type WSe2. Temporal and spatial control of the doping is achieved by varying the laser irradiation power and time, demonstrating wide tunability and high site selectivity with high stability. The laser-assisted doping method may enable a new avenue for functionalizing TMDCs for customized nanodevice applications.
- Kim, Eunpa,Ko, Changhyun,Kim, Kyunghoon,Chen, Yabin,Suh, Joonki,Ryu, Sang-Gil,Wu, Kedi,Meng, Xiuqing,Suslu, Aslihan,Tongay, Sefaattin,Wu, Junqiao,Grigoropoulos, Costas P.
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- Morphological characteristics in polycrystalline tungsten diselenide regulating transport properties lead to predominant thermoelectric performance
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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.
- Kim, Cham,Baek, Ju Young,Kim, Dong Hwan,Kim, Jong Tae,Lopez, David Humberto,Kim, Taewook,Kim, Hoyoung
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- In-plane thermal conductivity of disordered layered W Se2 and (W)x (W Se2) y superlattice films
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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.
- Mavrokefalos, Anastassios,Nguyen, Ngoc T.,Pettes, Michael T.,Johnson, David C.,Shi, Li
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- A 3D dendritic WSe2 catalyst grown on carbon nanofiber mats for efficient hydrogen evolution
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3D dendritic WSe2 on conductive carbon nanofiber mats (d-WSe2/CFM) was designed and synthesized by a diffusion-controlled CVD method. The d-WSe2/CFM was directly used as a cathode for the HER. The substantially improved HER performance is ascribed to the novel 3D structure with effectively exposed edge sites.
- Zou, Meiling,Zhang, Junfeng,Zhu, Han,Du, Mingliang,Wang, Qingfa,Zhang, Ming,Zhang, Xiangwen
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- Synthesis, crystal structure and physical properties of a novel quaternary selenide Cu6GeWSe8
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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.
- Chen, Genfu,Gu, Yadong,Ren, Zhian,Ruan, Binbin,Yang, Qingsong,Zhou, Menghu
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- ELECTRODEPOSITED TUNGSTEN SELENIDE FILMS.
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There is interest in developing inexpensive techniques for preparing large-area polycrystalline semiconductor thin films, particularly for applications in photoelectrochemical solar cells (PESC). An electrodeposition method for obtaining tungsten selenide films on a titanium substrate is described for the first time. An induced co-deposition mechanism is suggested. The first deposit is always Se which is followed by increasing W de position. Structural characterization was carried out by EDAX, TEM, and SEM studies.
- Chandra,Srivastava,Sahu
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- Solution-phase synthesis of highly conductive tungsten diselenide nanosheets
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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.
- Antunez, Priscilla D.,Webber, David H.,Brutchey, Richard L.
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- Graphene analogues of layered metal selenides
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Graphene analogues of MoSe2 and WSe2 have been prepared by three different chemical methods and characterized by electron microscopy and other methods. Graphene analogues of these diselenides as well as of GaSe have also been obtained by liquid-phase exfoliation. Raman spectra of the graphene analogues show significant changes relative to those of the bulk samples.
- Matte, H. S. S. Ramakrishna,Plowman, Blake,Datta, Ranjan,Rao
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- 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)
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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.
- O'Hare, P. A. G.,Lewis, Brett M.,Parkinson, B. A.
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- Exfoliation of bulk inorganic layered materials into nanosheets by the rapid quenching method and their electrochemical performance
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We report herein the results of our investigations on the synthesis of transition-metal dichalcogenide (TMDC) semiconductor layered materials of MoS2, WS2, MoSe2, and WSe2 by the rapid quenching method. The bulk powders were added to deionized water in a polypropylene tube and subsequently flushed with argon gas. Thirty rapid freezing (30 s in a liquid nitrogen bath) and heating (20 min in an oil bath at 60 °C) cycles were then carried out. The reaction product was obtained in a yield in excess of 60 wt.-%, which indicates that the method can be utilized on an industrial scale for the production of 2D nanosheets. The as-synthesized products were then characterized by TEM, which revealed nanosheet-like morphologies. Raman spectroscopy confirmed the high quality of the nanosheet samples. The exfoliated samples also showed good electrochemical performance. Of the TMDC samples investigated, the WSe2 nanosheets were found to give the best performance due to their uniform morphology, large surface area, and fewest number of defects.
- Chakravarty, Disha,Late, Dattatray J.
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- Novel magnetically separable Fe3O4-WSe2/NG photocatalysts: Synthesis and photocatalytic performance under visible-light irradiation
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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.
- An, Baihong,Liu, Yanan,Xu, Chengcheng,Wang, Han,Wan, Jun
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- Using ligands to control reactivity, size and phase in the colloidal synthesis of WSe2 nanocrystals
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Colloidal chemistry is leveraged for size- and phase-tuning of transition metal dichalcogenide nanomaterials. Specifically, nucleation and growth of colloidal WSe2 nanocrystals are controlled via mixtures of oleic acid (OA) and trioctylphosphine oxide. Increased OA yields slower nucleation, larger nanocrystals and a shift from the 2H to 1T′ phase.
- Geisenhoff, Jessica Q.,Tamura, Ashley K.,Schimpf, Alina M.
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- Low-Temperature Solution Synthesis of Transition Metal Dichalcogenide Alloys with Tunable Optical Properties
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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.
- Sun, Yifan,Fujisawa, Kazunori,Lin, Zhong,Lei, Yu,Mondschein, Jared S.,Terrones, Mauricio,Schaak, Raymond E.
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- MoSe2 and WSe2 nanotubes and related structures
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MoSe2 and WSe2 nanotubes are obtained by the reduction of the corresponding triselenides in hydrogen or by the decomposition of the ammonium selenometallates in a hydrogen atmosphere.
- Nath,Rao
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- Electronic energy states of tungsten dichalcogenides by low energy electron loss spectroscopy study
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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
- Ito, Toshimichi,Iwami, Motohiro,Hiraki, Akio
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- Chalcogen-vacancy group VI transition metal dichalcogenide nanosheets for electrochemical and photoelectrochemical hydrogen evolution
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Solar photoelectrochemical water splitting using the catalytic hydrogen evolution reaction (HER) is one of the most promising methods for producing hydrogen energy. Herein, we report the facile synthesis of chalcogen vacancy-rich (5-20%) transition metal dichalcogenide (TMD, i.e., MoS2, MoSe2, WS2, and WSe2) nanostructures for the (photo)electrocatalytic HER. Atomically resolved scanning transmission electron microscopy revealed the concentration of chalcogen (S and Se) vacancies, as well as the formation of double chalcogen vacancies at higher concentrations. Photocathodes consisting of a Si nanowire array sheathed in TMD layers exhibited excellent photoelectrocatalytic performance under AM 1.5 irradiation conditions. The photocurrent reached 30 mA cm-2 (at 0 V vs. RHE) with a high faradaic efficiency (90%) and negligible degradation of the HER for 3 h. The free-standing TMD nanosheets exhibit excellent electrocatalytic HER performance (an overpotential of 162-202 mV vs. RHE for 10 mA cm-2 and a Tafel slope of 70-84 mV dec-1 in 0.5 M H2SO4), which can be correlated with the vacancy concentration. A detailed structural analysis suggested that the chalcogen vacancies play a major role in determining the catalytic activity toward the HER, which in turn is responsible for the enhanced PEC performance. This journal is
- Kwak, In Hye,Kwon, Ik Seon,Lee, Jong Hyun,Lim, Young Rok,Park, Jeunghee
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- Observation of superconductivity in pressurized 2M WSe2 crystals
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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.
- Fang, Yuqiang,Dong, Qing,Pan, Jie,Liu, Hanyu,Liu, Pan,Sun, Yiyang,Li, Quanjun,Zhao, Wei,Liu, Bingbing,Huang, Fuqiang
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- New high-temperature Pb-catalyzed synthesis of inorganic nanotubes
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A new procedure for the synthesis of MoS2 nanotubes is reported, and additionally demonstrated for MoSe2, WS2, and WSe2. Highly concentrated sunlight creates continuous high temperatures, strong temperature gradients, and extended hot annealing regions, which, together with a metallic (Pb) catalyst, are conducive to the formation of different inorganic nanotubes. Structural characterization (including atomic resolution images) reveals a three-step reaction mechanism. In the first step, MoS2 platelets react with water-air residues, decompose by intense solar irradiation, and are converted to molybdenum oxide. Subsequently, the hot annealing environment leads to the growth of Pb-stabilized MoO3-x nanowhiskers. Shortly afterward, the surface of the MoO3-x starts to react with the sulfur vapor supplied by the decomposition of nearby MoS 2 platelets and becomes enveloped by MoS2 layers. Finally, the molybdenum oxide core is gradually transformed into MoS2 nanotubes. These findings augur well for similar syntheses of as yet unattained nanotubes from other metal chalcogenides.
- Brontvein, Olga,Albu-Yaron, Ana,Levy, Moshe,Tenne, Reshef,Stroppa, Daniel G.,Houben, Lothar,Popovitz-Biro, Ronit,Feuerman, Daniel,Gordon, Jeffrey M.
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p. 16379 - 16386,8
(2012)
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- Microwave and hydrothermal syntheses of WSe2 micro/nanorods and their application in supercapacitors
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WSe2 micro/nanorods were synthesized using one step microwave and hydrothermal methods. The as synthesized micro/nanorod samples of WSe2 were characterized using various characterization techniques such as SEM, TEM, Raman spectroscopy, X-ray diffraction, UV-visible and PL spectroscopy. The as synthesized samples were also tested for their applicability to use as cathode materials for supercapacitor applications. The WSe2 samples prepared by the microwave and hydrothermal methods (with use of tungstic acid as precursor) show noteworthy performance towards supercapacitor application. Our work opens a new avenue to use these simple methods to prepare various morphologies of inorganic nanomaterials and utilize them for various energy and nanoelectronics applications. This journal is
- Chakravarty, Disha,Late, Dattatray J.
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p. 21700 - 21709
(2015/03/31)
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- Structural, optical and microscopic studies of tungsten substituted molybdenum diselenide thin films
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A modified chemical bath deposition method has been developed to prepare Mo1-xWxSe2 layer type semiconductor thin films. Various preparative conditions of the thin films are outlined. The films were characterized by X-ray diffraction, optical absorption, electrical measurements and thermoelectric techniques. The grown films were found to be uniform, well adherent to substrate and brown in color. The X-ray diffraction (XRD) study indicates the polycrystalline nature in single hexagonal phase over whole range of composition. Analysis of absorption spectra gave direct type of band gap, the magnitude of which increases slightly as tungsten content in the film is increased and electrical conductivity at room temperature was found to be 10-5 to 10-2 (Ω cm)-1. All the films show n-type conductivity.
- Sathe,Hankare,Manikshete,Chate,Patil
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p. 187 - 193
(2010/09/11)
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- Solid-state metathesis as a quick route to transition-metal mixed dichalcogenides
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Solid-solution transition-metal dichalcogenides, traditionally synthesized from the elements at elevated temperatures over long periods of time, can now be prepared from rapid self-propagating reactions between transition-metal halides and alkali-metal mixed chalcogenides such as Na2(S,Se). The transition-metal dichalcogenide solid solution is isolated by simply washing away the byproduct salt. Powder X-ray diffraction and thermogravimetric analyses of the solid solutions Mo(S,Se)2 and W(S,Se)2 are presented. Although any composition can theoretically be prepared, the stoichiometry of the product is influenced by the temperatures attained during the course of the reaction. The products are characteristically enriched in the more volatile non-metal component relative to the alkali-metal mixed-chalcogenide precursor. The observed kinetic products and selective enrichment suggest that elemental intermediates may be involved in these reactions.
- Bonneau, Philippe R.,Jarvis Jr., Robert F.,Kaner, Richard B.
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p. 2127 - 2132
(2008/10/08)
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- Elaboration par CVD de WSe2 en couches minces
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This paper deals out with the preparation conditions of WSe2 thin films.Samples are prepared by using a classical CVD apparatus with WF6 and H2Se as carrier agents.Various substrates (quartz, silica, alumina and mica) have been used, the range of temperature being 300 deg C to 700 deg C.The films have been characterized by Rutherford Backscattering Spectroscopy (RBS), X-ray diffraction, Energy Dispersion Analysis of X-ray (EDAX), optical and electron microscopies.From RBS measurements it is found an atomic ratio NSe/NW = 2 within some particular conditions.The films are crystallized and present a preferential orientation.The optical absorption spectra are similar with those of single crystals and the photoelectrochemical stability is very good.
- Bourezg, R.,Couturier, G.,Salardenne, J.
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p. 2021 - 2030
(2007/10/02)
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- Intercalation processes in copper, zinc, and gallium diselenides of niobium, molybdenum, and tungsten with 2H structure
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There is now considerable interest in research on intercalation processes and and the physical properties of low-dimensional intercalated compounds. The overwhelming majority of experimental studies on intercalation of quasi-two-dimensional transition-metal dichalcogenides have been conducted for structures of the 2H-TaS2 type, and there are considerably fewer published studies on intercalation of dichalcogenides with structures of the 2H-MoS2 type, particularly disulfides and diselenides of tungsten and molybdenum. The latter have semiconductive properties and are widely used as antifriction materials in various friction units. The present paper describes some results of research on intercalation process in these systems. Formation of modulated intercalated structures has for the first time been established for intercalated low-dimensional compounds, utilizing copper, zinc, and gallium diselenides of tungsten and molybdenum with a 2H structure as a model. It was shown that intercalation occurs in different voids of the interlaminar space in the niobium copper diselenide system with a 2H structure: the octahedral (0 x 0.2), tetrahedral, and adjacent voids are involved, with most of the copper atoms going to the tetrahedral voids (0.33 x 0.75).
- Kulikov,Semenov-Kobzar,Aksel'rud,Lobova,Bogachev
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- Enthalpy of Formation of Tungsten Diselenide
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The enthalpy of formation of tungsten diselenide has been measured calorimetrically by direct synthesis (ΔHo298 = -154.2 +/- 2 kJ mole-1).The dissociation pressure of tungsten diselenide has been measured by the Knudsen method in the range 1173-1423 K, and from the enthalpy of dissociation (ΔH = 259.6 +/- 4 kJ mole-1) a value of -151.4 +/-4 kJ mole-1 has been recalculated for the standard enthalpy of formation.
- Zelikman, A. N.,Kolchin, Yu. O.,Golutvin, Yu. M.
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p. 519 - 521
(2007/10/02)
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- THERMODYNAMICS OF INCONGRUENTLY VAPORIZING TUNGSTEN DISELENIDE.
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The incongruent vaporization of WSe//2 was investigated by a simultaneous weight-loss-mass-spectrometric Knudsen effusion technique in the temperature range 1290-1720 K. For the reaction ( one-half )WSe//2(s) yields ( one-half )W(s) plus Se(g), DELTA H degree //2//9//8 equals . 311 plus or minus 3 kJ/mol.
- Schiffman,Franzen,Ziegler
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