DOCSLIB.ORG

United States Patent Office Patented Oct

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
United States Patent Office Patented Oct 3,472,621 United States Patent Office Patented Oct. 14, 1969 2 in yield does not justify the extra effort required to attain 3,472,621 such higher pressures. MOLYBDENUM DISELENDE HAVING A RHOM. As previously stated, the practice of this invention re BOHEDRAL CRYSTAL STRUCTURE AND METH OD OF PREPARING SAME quires a combination of both pressure and elevated tem Meyer S. Silverman, Norristown, Pa., assignor to Pennsalt peratures to convert the raw materials described above Chemicals Corporation, Philadelphia, Pa., a corpora into the new rhombohedral crystalline form of molyb tion of Pennsylvania denum diselenide. A temperature of at least about 800' No Drawing. Filed July 9, 1965, Ser. No. 470,907 C. is necessary, at least about 1600° C. being preferred. The portion of the term of the patent subsequent The practical upper temperature limit is about 2500 C. to May 28, 1985, has been disclaimed 10 The preferred range of operating temperatures is from Int. Cl. C01b 19/00; C01g 39/00 about 1600 C. to about 2000 C. The product MoSea U.S. Ct. 23-204 11 Claims will contain some hexagonal crystal form of the com pound in addition to the desired rhombohedral crystal form when the synthesis is conducted in the lower range 15 of temperatures, with an increase in temperature favoring ABSTRACT OF THE DISCLOSURE the yield of the rhombohedral form. It has been found Molybdenum diselenide having a rhombohedral crystal that at temperatures above about 1600 C., the product is structure and useful as a specialty lubricant is prepared essentially the rhombohedral crystal form. by Subjecting a mixture of elemental molybdenum and The relative amounts of the aforesaid raw materials in Selenium to the simultaneous effects of high heat and 20 the mixture subjected to the process of this invention are high pressure, i.e. a temperature of at least about 800 such as to provide an atomic ratio of molybdenum to C. and a pressure of at least about 10 kilobars. selenium in the charge generally within the range of about 1:2 to about 1:4. Although an excess of selenium greater than the 4 moles Se to one mole Mo is possible, 25 no advantage is gained, and if a purified product is desired This invention relates to a new form of molybdenum more unreacted selenium must be removed. The preferred diselenide and also to a method for preparing molyb atomic ratio of Mo to Se is within the range of about denum diselenide. More particularly, this invention con 1:2 to about 1:3, and most preferable is a ratio of 1:2.2. cerns a new compound of molybdenum and selenium hav The reaction period, which is not critical, may vary ing a rhombohedral crystal structure and the empirical 30 from about 1 minute to 24 hours, although the reaction formula MoSea, or expressed another way MoSea, and generally is completed in no more than about 5 minutes. a unique, high temperature, synthesis technique for pre Yields of from 75 to 100% of the rhombohedral crystal paring molybdenum diselenide. form of MoSea are obtained without difficulty in the Molybdenum diselenide having an hexagonal crystal practice of this process with reaction periods of from structure and a charcoal grey appearance is known. In 35 about 2 to 5 minutes. Unreacted selenium, which is quite accordance with this invention, it has been discovered volatile, may be removed from the product, if so desired, that the molybdenum diselenide having the rhombohedral by vacuum sublimation. crystal structure as described herein is prepared by sub The apparatus used in the illustrative examples that jecting, in the preferred embodiment, a mixture of ele follow is similar to that developed at the National Bureau mental molybdenum and elemental selenium to the com 40 of Standards and described in “Compact Multianvil bined action of extreme temperatures and pressures. The Wedge Type High Pressure Apparatus,” E. C. Lloyd, U.O. rhombohedral crystalline mloybdenum diselenide is a Hutton and D. P. Johnson in the Journal of Research of black, reflective, very soft, polycrystalline material. It has the National Bureau of Standards, vol. 63C, No. 1, July been discovered that heating the new rhombohedral form September, 1959, pages 59-64. In place of the 9A6' of MoSea under reduced pressures, e.g., at from about 45 tetrahedral sample holders used in the above reference, 900 to about 1000 C., and under pressures of less than %' holders with 4' anvil faces were employed in the about 25 mm. of Hg abs., converts the product into the examples which follow, and alternatively, 546' holders known, aforesaid, hexagonal crystal form of MoSea. were used with 34' anvil faces. A polyester film ("Mylar' In alternative embodiments of the process, the starting manufactured by Du Pont Company) was used between materials used can be compounds which are precursors 50 the anvil assemblies and the polytetrafluoroethylene sheet of the new molybdenum diselenide produced by the ap ("Teflon,” manufactured by Du Pont Company). Addi plication of the heat and pressure, i.e. those compounds tionally, a 0.003' wall boron nitride sleeve was used be which form MoSea in situ, for example, MoO--Se, tween the sample and the graphite heaters as electrical Mo--SeO2, MoC3--SeO2, and the hexagonal crystal form 55 insulation. Force was applied to the tetrahedral anvil sys of MoSe2. tem by a Watson-Stillman 100-ton hydraulic laboratory The pressure used to produce the molybdenum disele press. Pressure calibration was done by measuring the nide according to this invention, in simultaneous combina electrical resistance change of bismuth Samples. Pressure tion with heat acting on a mixture of molybdenum and was measured as a function of ram force and the three selenium, or a mixture of molybdenum and a precursor discontinuities were considered to occur at 25.4, 27.0 and of selenium, or a mixture of selenium and a precursor of 60 82 kilobars. In all of the preparations, a thin sleeve of molybdenum, or a mixture of precursors that yield molyb spectroscopic grade graphite was used as the heating ele denum diselenide in situ, is at least about 10 kilobars (one ment around the sample, and end plugs of the same ma kilobar equals 986.92 atmospheres), preferably at least terial isolated the sample from the platinum or silvered about 20 kilobars and more preferably at least about 40 65 tabs that carried the current from the anvils to the heat kilobars. The use of pressures in excess of 80 kilobars ing sleeve. Temperature calibrations were done by meas serves no practical purpose since the small improvement uring the electrical power input required to obtain tem 3,472,621 3 4. peratures which were indicated by a Chromel-Alumel TABLE I-Continued thermocouple, the tip of which was in good contract with the center of the graphite heating sleeve. The tempera Hexagonal, d, A.: Form tures reported here are thus the highest to which any 6.“ ------------------------------------ 78 part of the sample was subjected, and it should be recog 3.225 ----------------- - - - - - - - - - - - - - - - - - - 6 nized that the ends of the sample in each case were some 2.839 ----------------------------------- 63 what cooler. Experience in repeated calibrations indicates 2,788 ----------------------------------- 6 that the temperature values are uncertain by approximate 2.67 ----------------------------------- 7 ly 50 C., but the relative differences among the tem 2.369 ----------------------------------- 100 perature levels of the experiment are believed to be quite 2,151 ----------------------------------- 10 reliable. O 1914----------------------------------- 39 In each preparation the sample was first compressed in 1.641 ----------------------------------- 49 the high pressure apparatus, then heated, and held at the 1.615 ----------------------------------- 13 1591 ----------------------------------- 10 desired conditions for a measured period of time. The 1.464 ----------------------------------- 2 high pressure was then maintained until the power was 5 turned off and the sample had cooled to nearly ambient 1.422 ----------------------------------- 8 temperature. Cooling was very rapid in all cases. The 1.352 ---------------------------------- 13 product was removed as a compressed cylindrical pellet. 1.306 ----------------------- - - - - - - - - - - - - 6 1,246 ----------------------------------- 8 EXAMPLE 1. 1152 ----------------------------------- 33 20 A mixture of powdered molybdenum (99.8% purity, 'I' values are the relative intensity of the individual lines, relative to the strongest line in the pattern which is given the Fisher Scientific Company) and powdered selenium (tech Walue of 100. nical grade, 99-- percent purity, 200 mesh, Harshaw 'd' in Angstrom units is the interplanar distance between Chemical Corporation), the ratio of these raw materials lattice planes according to the Bragg Equation. in said mixture being one gram-mole of molybdenum to 25 It is well known that X-ray spectographs uniquely char 2.2 gram-moles of selenium, is charged to the above acterize crystalline structures, and therefore, the above described tetrahedral anvil apparatus. The mixture is com X-ray diffraction pattern for the new rhombohedral pressed to a pressure of 45 kilobars and then rapidly MoSe2 is a definitive description of the compound. heated to 1760 C. where it is held for 5 minutes. The A portion of the rhombohedral MoSea prepared above electrical power is switched off to quickly quench the 30 is heated to 1000 C. in a vacuum (25 mm. Hg) and reaction. After a cooling period of about 5 minutes, the held under these
Load more

Recommended publications
  • Two-Dimensional Material-Based Colorimetric Biosensors: a Review
    biosensors Review Two-Dimensional Material-Based Colorimetric Biosensors: A Review Danzhu Zhu, Bin Liu and Gang Wei * College of Chemistry and Chemical Engineering, Qingdao University, Qingdao 266071, China; [email protected] (D.Z.); [email protected] (B.L.) * Correspondence: [email protected]; Tel.: +86-150-6624-2101 Abstract: Two-dimensional (2D) materials such as graphene, graphene oxide, transition metal oxide, MXene and others have shown high potential for the design and fabrication of various sensors and biosensors due to their 2D layered structure and unique properties. Compared to traditional fluorescent, electrochemical, and electrical biosensors, colorimetric biosensors exhibit several ad- vantages including naked-eye determination, low cost, quick response, and easy fabrication. In this review, we present recent advances in the design, fabrication, and applications of 2D material-based high-performance colorimetric biosensors. Potential colorimetric sensing mechanisms and optimal material selection as well as sensor fabrication are introduced in brief. In addition, colorimetric biosensors based on different 2D materials such as graphene, transition metal dichalcogenide/oxide, MXenes, metal–organic frameworks, and metal nanoplates for the sensitive detection of DNA, proteins, viruses, small molecules, metallic ions, and others are presented and discussed in detail. This work will be helpful for readers to understand the knowledge of 2D material modification, nanozymes, and the synthesis of hybrid materials; meanwhile, it could be valuable to promote the design, fabrication, and applications of 2D material-based sensors and biosensors in quick bioanalysis and disease diagnostics. Keywords: 2D materials; nanoparticles; nanozymes; hybrid materials; colorimetric biosensors Citation: Zhu, D.; Liu, B.; Wei, G. Two-Dimensional Material-Based Colorimetric Biosensors: A Review.
    [Show full text]
  • Growth of Two-Dimensional Molybdenum Disulfide Via Chemical Vapor Deposition
    Wright State University CORE Scholar Browse all Theses and Dissertations Theses and Dissertations 2019 Growth of Two-Dimensional Molybdenum Disulfide via Chemical Vapor Deposition Zachary Durnell Ganger Wright State University Follow this and additional works at: https://corescholar.libraries.wright.edu/etd_all Part of the Engineering Science and Materials Commons Repository Citation Ganger, Zachary Durnell, "Growth of Two-Dimensional Molybdenum Disulfide via Chemical aporV Deposition" (2019). Browse all Theses and Dissertations. 2174. https://corescholar.libraries.wright.edu/etd_all/2174 This Thesis is brought to you for free and open access by the Theses and Dissertations at CORE Scholar. It has been accepted for inclusion in Browse all Theses and Dissertations by an authorized administrator of CORE Scholar. For more information, please contact [email protected]. GROWTH OF TWO-DIMENSIONAL MOLYBDENUM DISULFIDE VIA CHEMICAL VAPOR DEPOSITION A thesis submitted in partial fulfillment of the requirements for the degree of Master of Science in Materials Science and Engineering By ZACHARY DURNELL GANGER B.S.M.S.E. Wright State University, 2015 2019 Wright State University WRIGHT STATE UNIVERSITY GRADUATE SCHOOL March 28th, 2019 I HEREBY RECOMMEND THAT THE THESIS PREPARED UNDER MY SUPERVISION BY Zachary Durnell Ganger ENTITLED Growth of Two Dimensional Molybdenum Disulfide via Chemical Vapor Deposition BE ACCEPTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF Master of Science in Materials Science and Engineering. Committee on Final Examination ______________________________ Hong Huang, Ph.D. ________________________________ Thesis Director Hong Huang, Ph.D. Joseph C. Slater, Ph.D., P.E. ________________________________ Chair, Department of Mechanical and Materials Engineering Yan Zhuang, Ph.D.
    [Show full text]
  • Evaluating the Effect of Varying the Metal Precursor in the Colloidal Synthesis of Mose2 Nanomaterials and Their Application As
    nanomaterials Article Evaluating the Effect of Varying the Metal Precursor in the Colloidal Synthesis of MoSe2 Nanomaterials and Their Application as Electrodes in the Hydrogen Evolution Reaction Zakhele Ndala 1, Ndivhuwo Shumbula 1 , Siyabonga Nkabinde 1, Tshwarela Kolokoto 1, Obakeng Nchoe 1, Poslet Shumbula 2, Zikhona N. Tetana 1,3,4, Ella C. Linganiso 1,3,4, Siziwe S. Gqoba 1,* and Nosipho Moloto 1,* 1 Molecular Sciences Institute, School of Chemistry, University of the Witwatersrand, Private Bag 3, Wits 2050, South Africa; [email protected] (Z.N.); [email protected] (N.S.); [email protected] (S.N.); [email protected] (T.K.); [email protected] (O.N.); [email protected] (Z.N.T.); [email protected] (E.C.L.) 2 Department of Chemistry, University of Limpopo Private Bag x1106, Sovenga 0727, South Africa; [email protected] 3 DST/NRF Centre of Excellence in Strong Materials, University of the Witwatersrand, Private Bag 3, Wits 2050, South Africa 4 Microscopy and Microanalysis Unit, University of the Witwatersrand, Private Bag 3, Johannesburg, Wits 2050, South Africa * Correspondence: [email protected] (S.S.G.); [email protected] (N.M.); Tel.: +27-11-7176-774 or +27-11-7176-756 (S.S.G.); Fax: +27-11-7176-749 (N.M.) Received: 7 July 2020; Accepted: 24 July 2020; Published: 9 September 2020 Abstract: Herein we report on the use of different metal precursors in the synthesis of MoSe2 nanomaterials in order to control their morphology.
    [Show full text]
  • Chemical Vapor Deposition Growth of Monolayer Mose2 Nanosheets Jonathan C
    Nano Research 1 DOINano 10.1007/s12274Res ‐014‐0147‐z Chemical vapor deposition growth of monolayer MoSe2 nanosheets Jonathan C. Shaw1, Hailong Zhou1, Yu Chen2, Nathan O. Weiss2, Yuan Liu2, Yu Huang2,3, Xiangfeng 1,3 Duan () Nano Res., Just Accepted Manuscript • DOI: 10.1007/s12274-014-0147-z http://www.thenanoresearch.com on January 15, 2014 © Tsinghua University Press 2014 Just Accepted This is a “Just Accepted” manuscript, which has been examined by the peer‐review process and has been accepted for publication. A “Just Accepted” manuscript is published online shortly after its acceptance, which is prior to technical editing and formatting and author proofing. Tsinghua University Press (TUP) provides “Just Accepted” as an optional and free service which allows authors to make their results available to the research community as soon as possible after acceptance. After a manuscript has been technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Please note that technical editing may introduce minor changes to the manuscript text and/or graphics which may affect the content, and all legal disclaimers that apply to the journal pertain. In no event shall TUP be held responsible for errors or consequences arising from the use of any information contained in these “Just Accepted” manuscripts. To cite this manuscript please use its Digital Object Identifier (DOI®), which is identical for all formats of publication. Chemical vapor deposition growth of monolayer MoSe2 nanosheets ,§ ,§ Jonathan C. Shaw1 , Hailong Zhou1 , Yu Chen2, Nathan O. Weiss2, Yuan Liu2, Yu Huang2,3, Xiangfeng Duan1,3,* 1.
    [Show full text]
  • Recent Advances in Ambipolar Transistors for Functional Applications
    REVIEW Ambipolar Transistors www.afm-journal.de Recent Advances in Ambipolar Transistors for Functional Applications Yi Ren, Xiaoyang Yang, Li Zhou, Jing-Yu Mao, Su-Ting Han,* and Ye Zhou* communities. For the sake of the suc- Ambipolar transistors represent a class of transistors where positive (holes) cessful implementation of their intricate and negative (electrons) charge carriers both can transport concurrently functionalities, diverse fundamental elec- within the semiconducting channel. The basic switching states of ambipolar tronic constituents are imperative to act transistors are comprised of common off-state and separated on-state mainly as functional system blocks. As one of the most significant components, transistors impelled by holes or electrons. During the past years, diverse materials are are the foundation and key ingredients of synthesized and utilized for implementing ambipolar charge transport and modern electronic devices and products.[1] their further emerging applications comprising ambipolar memory, synaptic, Since the 1950s, transistors have gradually logic, and light-emitting transistors on account of their special bidirectional replaced vacuum tubes and finally realized carrier-transporting characteristic. Within this review, recent developments mass production of integrated circuits of ambipolar transistor field involving fundamental principles, interface and microprocessors. Transistors pos- sessing advantages of low cost, flexibility modifications, selected semiconducting material systems, device structures,
    [Show full text]
  • Engineering Molybdenum Diselenide and Its Reduced Graphene Oxide Hybrids for Efficient Electrocatalytic Hydrogen Evolution
    Article Cite This: ACS Appl. Nano Mater. 2018, 1, 2143−2152 www.acsanm.org Engineering Molybdenum Diselenide and Its Reduced Graphene Oxide Hybrids for Efficient Electrocatalytic Hydrogen Evolution † † ‡ ∥ † † Swagotom Sarker, Jonathan Peters, Xinqi Chen, Binsong Li, Gen Chen, Litao Yan, † § † † Stephanie K. Richins, Sanjib Das, Meng Zhou, and Hongmei Luo*, † Department of Chemical and Materials Engineering, New Mexico State University, Las Cruces, New Mexico 88003, United States ‡ § Northwestern University Atomic and Nanoscale Characterization Experimental (NUANCE) Center and Department of Materials Science and Engineering, Northwestern University, Evanston, Illinois 60208, United States ∥ Tsinghua Innovation Center in Dongguan, Building 8, Sci& Tech. Innovation Park, Songshan Lake National High-Tech Industrial Development Zone, Dongguan, Guangdong 523808, P. R. China *S Supporting Information ABSTRACT: We report the hydrogen evolution reaction (HER) with molybdenum diselenide (MoSe2) and its reduced graphene oxide (rGO) hybrids synthesized by a microwave process followed by annealing at 400 °C. The content of GO was varied to understand its role in the electrocatalytic activities. Electrochemical performance of the as-synthe- sized and the annealed catalysts underscores (i) a requirement of catalytic activation of the as-synthesized samples, (ii) an apparent shift in the onset potential as a result of annealing, and (iii) striking changes in the Tafel slope as well as the overpotential. The results clearly reveal that partially crystalline plain MoSe2 is more elctroactive in comparison to its annealed counterpart, whereas annealing is advantageous to MoSe2/rGO. Improved HER performances of the annealed MoSe2/rGO hydrids arise from the ff synergistic e ect between active MoSe2 and rGO of improved conductivity.
    [Show full text]
  • Electrical Control of Neutral and Charged Excitons in a Monolayer Semiconductor
    Electrical Control of Neutral and Charged Excitons in a Monolayer Semiconductor Jason S. Ross 1*, Sanfeng Wu 2*, Hongyi Yu 3, Nirmal J. Ghimire 4,5 , Aaron M. Jones 2, Grant Aivazian 2, Jiaqiang Yan 5,6 , David G. Mandrus 4,5,6 , Di Xiao 7, Wang Yao 3, Xiaodong Xu 1,2† 1 Department of Material Science and Engineering, University of Washington, Seattle, Washington 98195, USA 2 Department of Physics, University of Washington, Seattle, Washington 98195, USA 3 Department of Physics and Center of Theoretical and Computational Physics, The University of Hong Kong, Hong Kong, China 4 Department of Physics and Astronomy, University of Tennessee, Knoxville, Tennessee 37996, USA 5 Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee, 37831, USA 6 Department of Materials Science and Engineering, University of Tennessee, Knoxville, Tennessee, 37996, USA 7 Department of Physics, Carnegie Mellon University, Pittsburg, PA 15213, USA * These authors contributed equally to the work. † Email: [email protected] Abstract: Monolayer group VI transition metal dichalcogenides have recently emerged as semiconducting alternatives to graphene in which the true two-dimensionality (2D) is expected to illuminate new semiconducting physics. Here we investigate excitons and trions (their singly charged counterparts) which have thus far been challenging to generate and control in the ultimate 2D limit. Utilizing high quality monolayer molybdenum diselenide (MoSe 2), we report the unambiguous observation and electrostatic tunability of charging effects in positively charged (X +), neutral (X o), and negatively charged (X -) excitons in field effect transistors via photoluminescence. The trion charging energy is large (30 meV), enhanced by strong confinement and heavy effective masses, while the linewidth is narrow (5 meV) at temperatures below 55 K.
    [Show full text]
  • Cztse Solar Cells Prepared by Electrodeposition of Cu/Sn/Zn Stack Layer Followed by Selenization at Low Se Pressure
    Yao et al. Nanoscale Research Letters 2014, 9:678 http://www.nanoscalereslett.com/content/9/1/678 NANO EXPRESS Open Access CZTSe solar cells prepared by electrodeposition of Cu/Sn/Zn stack layer followed by selenization at low Se pressure Liyong Yao1, Jianping Ao1*, Ming-Jer Jeng2*, Jinlian Bi1, Shoushuai Gao1, Qing He1, Zhiqiang Zhou1, Guozhong Sun1, Yun Sun1, Liann-Be Chang2 and Jian-Wun Chen2 Abstract Cu2ZnSnSe4 (CZTSe) thin films are prepared by the electrodeposition of stack copper/tin/zinc (Cu/Sn/Zn) precursors, followed by selenization with a tin source at a substrate temperature of 530°C. Three selenization processes were performed herein to study the effects of the source of tin on the quality of CZTSe thin films that are formed at low Se pressure. Much elemental Sn is lost from CZTSe thin films during selenization without a source of tin. The loss of Sn from CZTSe thin films in selenization was suppressed herein using a tin source at 400°C (A2) or 530°C (A3). A copper- poor and zinc-rich CZTSe absorber layer with Cu/Sn, Zn/Sn, Cu/(Zn + Sn), and Zn/(Cu + Zn + Sn) with metallic element ratios of 1.86, 1.24, 0.83, and 0.3, respectively, was obtained in a selenization with a tin source at 530°C. The crystallized CZTSe thin film exhibited an increasingly (112)-preferred orientation at higher tin selenide (SnSex) partial pressure. The lack of any obvious Mo-Se phase-related diffraction peaks in the X-ray diffraction (XRD) diffraction patterns may have arisen from the low Se pressure in the selenization processes.
    [Show full text]
  • Pulsed Electrodeposition and Characterization of Molybdenum Diselenide Thin Film
    Materials Research Bulletin 40 (2005) 135–147 www.elsevier.com/locate/matresbu Pulsed electrodeposition and characterization of molybdenum diselenide thin film S. Mary Delphinec, M. Jayachandranb, C. Sanjeevirajaa,* aDepartment of Physics, Alagappa University, Karaikudi 630003, India bElectrochemical Materials Science Division, Central Electrochemical Research Institute, Karaikudi 630006, India cDepartment of Physics, Holy Cross College, Nagercoil 629004, India Received 15 November 2003; received in revised form 14 May 2004; accepted 9 September 2004 Abstract Molybdenum dichalcogenides are semiconductors with layered type structure, which can act as efficient electrodes in the realization of photoelectrochemical solar cells. The main advantage of this molybdenum diselenide (MoSe2) semiconductor is the prevention of electrolyte corrosion because of the phototransitions involving non-bonding d–d orbital of the Mo atoms. Polycrystalline molybdenum diselenide thin films are prepared by pulsed electrodeposition on conducting glass and titanium substrates in galvanostatic mode from an ammoniacal solution of H2MoO4 and SeO2. The growth kinetics of the film was studied and the deposition parameters such as electrolyte bath concentration, bath temperature, time of deposition, deposition current, pH of the electrolyte and duty cycle of the current are optimized. X-ray diffraction analysis of the as deposited and annealed films showed the presence of highly textured MoSe2 films with polycrystalline nature. EDAX spectrum of the surface composition confirms the nearly stoichiometric MoSe2 nature of the film. Surface morphology studies by scanning electron microscope (SEM) shows that the films are pinhole free and of device quality nature. The optical absorption spectra show an indirect band gap value of 1.16 eV. Conductivity measurements were carried out at different temperatures and electrical constants such as activation energy, trapped energy state and barrier height were calculated.
    [Show full text]
  • Density-Functional Study of Lixmos2 Intercalates (0 ≤ X ≤ 1)
    Density-functional study of LixMoS2 intercalates (0 ≤ x ≤ 1) Andrey N. Enyashin,*a,b, and Gotthard Seiferta a Physical Chemistry Department, Technical University Dresden, Bergstr. 66b, 01062 Dresden, Germany b Institute of Solid State Chemistry UB RAS, Pervomayskaya Str. 91, 620990 Ekaterinburg, Russia [email protected]; [email protected] RECEIVED DATE The stability of Lithium intercalated 2H- and 1T allotropes of Molybdenum disulfide (LixMoS2 ) is studied within a density-functional theory framework as function of the Li content (x) and the intercalation sites. Octahedral coordination of Li interstitials in the van der Waals gap is found as the most favorite for both allotropes. The critical content of Lithium, required for the initialization of a 2H→1T phase transition is estimated to x ≈ 0.4. For smaller Li contents the hexagonal 2H crystal structure is not changed, while 1T-LixMoS2 compounds adopt a monoclinic lattice. All allotropic forms of LixMoS2 - excluding the monoclinic Li1.0MoS2 structure - show metallic-like character. The monoclinic Li1.0MoS2 is a semiconductor with a band gap of 1.1 eV. Finally, the influence of Li intercalation on the stability of multiwalled MoS2 nanotubes is discussed within a phenomenological model. KEYWORDS Molybdenum sulfide; Intercalate; Phase Transition; Electrode Material. *Corresponding author: e-mail: [email protected] Phone: +7 (343) 362 3115 Fax: +7 (343) 374 4495 Address: Institute of Solid State Chemistry UB RAS, Pervomayskaya Str. 91, 620990 Ekaterinburg, Russia 1 1. Introduction Layered transition-metal dichalcogenides have been the subject of numerous studies as materials with distinct tribological, photoelectrical, optical and catalytical properties.1-4 The layer structure allows also the intercalation of atoms, molecules or ions between the layers.5 Of special interest is the intercalation with Lithium, which can open the application as electrode materials for batteries with a high energy storage.
    [Show full text]
  • Scalable CVD Process for Making 2-D Molybdenum Diselenide 8 April 2014, by Jade Boyd
    Scalable CVD process for making 2-D molybdenum diselenide 8 April 2014, by Jade Boyd properties of molybdenum diselenide in a number of applications," said study leader Pulickel Ajayan, chair of Rice's Department of Materials Science and NanoEngineering. "Unlike graphene, which can now easily be made in large sheets, many interesting 2-D materials remain difficult to synthesize. Now that we have a stable, efficient way to produce 2-D molybdenum diselenide, we are planning to expand this robust procedure to other 2-D materials." In the Rice study, Ajayan and colleagues tested their atomically thin layers of molybdenum diselenide by building a field effect transistor (FET), a commonly used device in the microelectronic industry. Tests of the FET found the electronic This image from a scanning transmission electron properties of the molybdenum diselenide layers microscope shows the individual atoms in a two- were significantly better than those of molybdenum dimensional sheet of molybdenum diselenide. Credit: E. disulfide; the latter is a similar material that has Ringe/Rice University been more extensively studied because it was easier to fabricate. For example, the FET tests found that the electron mobility of Rice's molybdenum diselenide was higher than that of (Phys.org) —Nanoengineering researchers at Rice CVD-grown, molybdenum disulfide. University and Nanyang Technological University in Singapore have unveiled a potentially scalable In solid-state physics, electron mobility refers to method for making one-atom-thick layers of how quickly electrons pass through a metal or molybdenum diselenide—a highly sought semiconductor in the presence of an electric field. semiconductor that is similar to graphene but has Materials with high electron mobility are often better properties for making certain electronic preferred to reduce power consumption and devices like switchable transistors and light- heating in microelectronic devices.
    [Show full text]
  • Temperature Dependence of the Dielectric Function of Monolayer Mose2
    www.nature.com/scientificreports OPEN Temperature Dependence of the Dielectric Function of Monolayer MoSe2 Received: 5 December 2017 Han Gyeol Park1, Tae Jung Kim2, Farman Ullah 3, Van Long Le1, Hoang Tung Nguyen1, Accepted: 5 February 2018 Yong Soo Kim3 & Young Dong Kim1 Published: xx xx xxxx The dielectric function ε=ε+12iε of monolayer molybdenum diselenide (MoSe2) is obtained and analyzed at temperatures from 31 to 300 K and at energies from 0.74 to 6.42 eV. The sample is a large- area, partially discontinuous monolayer (submonolayer) flm of MoSe2 grown on a sapphire substrate by selenization of pulsed laser deposited MoO3 flm. Morphological and optical characterizations verifed the excellent quality of the flm. The MoSe2 data were analyzed using the efective medium approximation, which treats the flm and bare substrate regions as a single layer. Second derivatives of ε with respect to energy were numerically calculated and analyzed with standard lineshapes to extract accurate critical-point (CP) energies. We fnd only 6 CPs for monolayer MoSe2 at room temperature. At cryogenic temperatures 6 additional structures are resolved. The separations in the B- and C-excitonic peaks are also observed. All structures blue-shift and sharpen with decreasing temperature as a result of the reducing lattice constant and electron-phonon interactions. The temperature dependences of the CP energies were determined by ftting the data to the phenomenological expression that contains the Bose-Einstein statistical factor and the temperature coefcient. Over the last few years, knowledge of two-dimensional (2-D) materials has rapidly expanded due to the enor- mous interest in nanotechnology and various unique physical and chemical properties based on dimensionality1.
    [Show full text]