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Sample records for hueckel mo band

  1. Collective Band Structures in Neutron-Rich 108Mo Nucleus

    Institute of Scientific and Technical Information of China (English)

    DING Huai-Bo; WANG Jian-Guo; XU Qiang; ZHU Sheng-Jiang; J. H. Hamilton; A. V. Ramayya; J. K. Hwang; Y. X. Luo; J. O. Rasmussen; I. Y. Lee; CHE Xing-Lai

    2007-01-01

    High spin states in the neutron-rich 108Mo nucleus are studied by measuring prompt γ-rays following the spontaneous fission of 252Cf with a Gammasphere detector array. The ground-state band is confirmed, and the one-phonon γ-vibrational band is updated with spin up to 12 h. A new collective band with the band head level at 1422.4 keV is suggested as a two-phonon γ-vibrational band. Another new band is proposed as a two-quasi-proton excitation band. Systematic characteristics of the collective bands are discussed.

  2. Atomic-Monolayer MoS2 Band-to-Band Tunneling Field-Effect Transistor

    KAUST Repository

    Lan, Yann Wen

    2016-09-05

    The experimental observation of band-to-band tunneling in novel tunneling field-effect transistors utilizing a monolayer of MoS2 as the conducting channel is demonstrated. Our results indicate that the strong gate-coupling efficiency enabled by two-dimensional materials, such as monolayer MoS2, results in the direct manifestation of a band-to-band tunneling current and an ambipolar transport.

  3. Chiral vibrations and collective bands in 104Mo

    Science.gov (United States)

    Musangu, Brooks; Wang, E. H.; Zachary, C. J.; Eldridge, J. H.; Hamilton, J. H.; Ramayya, A. V.; Rasmussen, J. O.; Luo, Y. X.; Ter-Akopian, G. M.; Oganessian, Yu. Ts.; Zhu, S. J.

    2016-09-01

    High spin states of the neutron-rich 104Mo nucleus which is known to be triaxial have been reinvestigated by analyzing the γ-rays in the spontaneous fission of 252Cf with Gammasphere. Both γ- γ- γ and γ- γ- γ- γ coincidence data were analyzed. A new ΔI=1 band has been discovered. The new band is proposed to have a tentative 5- band head and form a class of chiral doublets with another 4- band previously found by our group. Angular correlation measurements have been performed to determine spin and parity of the 4- chiral band head. The energies of the two sets of chiral bands are very similar to the chiral bands observed in 106Mo, e.g. the two 5- levels in 104Mo are at 2211.9 and 2276.8 keV with ΔE=65 keV and in 106Mo, 1952.4 and 2090.6 keV with ΔE=138 keV. Now at every spin 5-, 6-, 7-, 8-, the separation energies of the same spin states are about a factor of two smaller than in 106Mo. This indicates even better agreement with expectations for two sets of chiral bands. Furman Advantage, Furman University.

  4. Collective Bands in Neutron-Rich 104Mo Nucleus

    Institute of Scientific and Technical Information of China (English)

    杨利明; 姜卓; 全明吉; J. H. Hamilton; A. V. Ramayya; J. K. Hwang; X. Q. Zhang; B. R. S. Babu; J. Komicki; E. F. Jones; W. C. Ma; 朱胜江; J. D. Cole; R. Aryaeinejad; M. W. Drigert; I. Y. Lee; J. O. Rasmussen; M. A. Stover; G. M. Ter-Akopian; A. V. Daniel; 李科; 朱凌燕; 甘翠云; 萨哈伊; 龙桂鲁; 许瑞清; 张征

    2001-01-01

    Levels in the neutron-rich 104Mo nucleus have been investigated by observing prompt γ-rays from the spontaneous fission of 252Cf with the Gammasphere detector array. The ground-state band, the one-phonon and the twophonon γ-vibrational bands as well as a quasiparticle band have been confirmed and expanded with spin up to 14h. Other two side bands probably built on new quasiparticle states are identified. The possible configurations for the quasiparticle bands are discussed. Two of the quasiparticle bands show larger moments of inertia and may have pair-free characteristics. The levels of the ground-state band, the one-phonon γ-band and the two-phonon γ-band calculated from a general collective model are in close agreement with the experimental data.

  5. Microwave irradiation induced band gap tuning of MoS2-TiO2 nanocomposites

    Science.gov (United States)

    Shakya, Jyoti; Mohanty, T.

    2016-05-01

    The MoS2-TiO2 nanocomposites have been synthesized by sol-gel method and characterized by different microscopic and spectroscopic techniques. The crystallinity of these nanocomposites has been confirmed by X-ray diffraction (XRD) analysis. The Raman spectrum of MoS2-TiO2 nanocomposites consists of three distinct peaks (E1 g, E1 2g and A1g) which are associated with TiO2 and MoS2. The morphological study is carried out by scanning electron microscope. The effect of microwave irradiation on the band gap of MoS2-TiO2 nanocomposites has been investigated; it is observed that the microwave irradiation causes decrease in the band gap of MoS2-TiO2 nanocomposites. The microwave treated MoS2-TiO2 thin films offers a novel process route in treating thin films for commercial applications.

  6. Band Alignment and Minigaps in Monolayer MoS2-Graphene van der Waals Heterostructures.

    Science.gov (United States)

    Pierucci, Debora; Henck, Hugo; Avila, Jose; Balan, Adrian; Naylor, Carl H; Patriarche, Gilles; Dappe, Yannick J; Silly, Mathieu G; Sirotti, Fausto; Johnson, A T Charlie; Asensio, Maria C; Ouerghi, Abdelkarim

    2016-07-13

    Two-dimensional layered MoS2 shows great potential for nanoelectronic and optoelectronic devices due to its high photosensitivity, which is the result of its indirect to direct band gap transition when the bulk dimension is reduced to a single monolayer. Here, we present an exhaustive study of the band alignment and relativistic properties of a van der Waals heterostructure formed between single layers of MoS2 and graphene. A sharp, high-quality MoS2-graphene interface was obtained and characterized by micro-Raman spectroscopy, high-resolution X-ray photoemission spectroscopy (HRXPS), and scanning high-resolution transmission electron microscopy (STEM/HRTEM). Moreover, direct band structure determination of the MoS2/graphene van der Waals heterostructure monolayer was carried out using angle-resolved photoemission spectroscopy (ARPES), shedding light on essential features such as doping, Fermi velocity, hybridization, and band-offset of the low energy electronic dynamics found at the interface. We show that, close to the Fermi level, graphene exhibits a robust, almost perfect, gapless, and n-doped Dirac cone and no significant charge transfer doping is detected from MoS2 to graphene. However, modification of the graphene band structure occurs at rather larger binding energies, as the opening of several miniband-gaps is observed. These miniband-gaps resulting from the overlay of MoS2 and the graphene layer lattice impose a superperiodic potential.

  7. Determination of band offsets at GaN/single-layer MoS2 heterojunction

    KAUST Repository

    Tangi, Malleswararao

    2016-07-25

    We report the band alignment parameters of the GaN/single-layer (SL) MoS2 heterostructure where the GaN thin layer is grown by molecular beam epitaxy on CVD deposited SL-MoS2/c-sapphire. We confirm that the MoS2 is an SL by measuring the separation and position of room temperature micro-Raman E1 2g and A1 g modes, absorbance, and micro-photoluminescence bandgap studies. This is in good agreement with HRTEM cross-sectional analysis. The determination of band offset parameters at the GaN/SL-MoS2 heterojunction is carried out by high-resolution X-ray photoelectron spectroscopy accompanying with electronic bandgap values of SL-MoS2 and GaN. The valence band and conduction band offset values are, respectively, measured to be 1.86 ± 0.08 and 0.56 ± 0.1 eV with type II band alignment. The determination of these unprecedented band offset parameters opens up a way to integrate 3D group III nitride materials with 2D transition metal dichalcogenide layers for designing and modeling of their heterojunction based electronic and photonic devices.

  8. Observation of Rotational Bands in Neutron-Rich 106Mo Nucleus

    Institute of Scientific and Technical Information of China (English)

    许瑞清; 甘翠云; 张征; 姜卓; 肖树冬; W.C.Ma; J.Kormicki; E. F. Jones; J. D. Cole; R. Aryaeinejad; M. W. Drigert; 朱胜江; I. Y. Lee; J. O. Rasmussen; M. A. Stoyer; G. M. Ter-Akopian; A. V. Daniel; J.H.Hamilton; A.V.Ramayya; J K.Hwang; X.Q.Zhang; 李科; 杨利明; 朱凌燕

    2002-01-01

    The rotational bands up to a spin of 16h in the neutron-rich 106Mo nucleus have been investigated by measuring high-fold prompt γ-ray coincidence events following spontaneous fission of 252 Cf with a Gammasphere detector array. The ground-state band, the one-phonon and two-phonon γ-vibrational bands, as well as a quasi-particle band have been confirmed and expanded. The other four collective rotational bands, three proposed as twoquasi-particle bands and one proposed as a β-vibrational band, have been newly observed. The characteristics of these collective bands and the possible configurations for the quasi-particle bands are discussed.

  9. Search for Double γ-Vibrational Bands in Neutron-Rich 105Mo Nucleus

    Institute of Scientific and Technical Information of China (English)

    DING Huai-Bo; CHEN Yong-Jing; LI Ming-Liang; ZHU Sheng-Jiang; J. H. Hamilton; A. V. Ramayya; J. K. Hwang; Y. X. Luo; J. O. Rasmussen; I. Y. Lee; CHE Xing-Lai

    2006-01-01

    Levels in the neutron-rich 105 Mo nucleus have been investigated by observing prompt γ-rays following the spon taneous fission fragments of 252 Cf with the Gammasphere detector array. The yrast band has been confirmed and updated. The other two collective bands with the band head levels at 870.5 and 1534.6 keV are newly observed,and they are suggested as the candidates for one-phonon K = 9/2 and two-phonon K = 13/2 double γ-vibrational bands, respectively. Systematic characteristics of these bands have been discussed.

  10. Development of banded microstructure in 34CrNiMo6 steel

    Directory of Open Access Journals (Sweden)

    A. Nagode

    2016-07-01

    Full Text Available In this paper the development of a banded microstructure in hot-rolled 34CrNiMo6 steel which consisted of bainitic and martensitic bands is explained. The chemical compositions of the bands were measured with energy dispersive x-ray spectroscopy (EDS, which showed that the martensitic bands contained more alloying elements (Mn, Cr, Mo, Si than bainitic bands. By using Oberhoffer reagent, the segregations of phosphorus were also revealed. These phosphorus segregations coincided with the positive segregations of the alloying elements. The continuous cooling transformation (CCT diagrams of steel were calculated. They confirmed the formation of martensite in positive segregations and the formation of bainite in negative segregations.

  11. Band renormalization and spin polarization of MoS{sub 2} in graphene/MoS{sub 2} heterostructures

    Energy Technology Data Exchange (ETDEWEB)

    Coy-Diaz, Horacio; Batzill, Matthias [Department of Physics, University of South Florida, Tampa, FL (United States); Bertran, Francois; Chen, Chaoyu; Avila, Jose; Rault, Julien; Le Fevre, Patrick; Asensio, Maria C. [Synchrotron SOLEIL, L' Orme des Merisiers, Gif sur Yvette (France)

    2015-12-15

    Transition metal dichalcogenides exhibit spin-orbit split bands at the K-point that become spin polarized for broken crystal inversion symmetry. This enables simultaneous manipulation of valley and spin degrees of freedom. While the inversion symmetry is broken for monolayers, we show here that spin polarization of the MoS{sub 2} surface may also be obtained by interfacing it with graphene, which induces a space charge region in the surface of MoS{sub 2}. Polarization induced symmetry breaking in the potential gradient of the space charge is considered to be responsible for the observed spin polarization. In addition to spin polarization we also observe a renormalization of the valence band maximum (VBM) upon interfacing of MoS{sub 2} with graphene. The energy difference between the VBM at the Γ-point and K-point shifts by ∝150 meV between the clean and graphene covered surface. (copyright 2015 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  12. Determination of band alignment in the single-layer MoS2/WSe2 heterojunction

    KAUST Repository

    Chiu, Ming-Hui

    2015-07-16

    The emergence of two-dimensional electronic materials has stimulated proposals of novel electronic and photonic devices based on the heterostructures of transition metal dichalcogenides. Here we report the determination of band offsets in the heterostructures of transition metal dichalcogenides by using microbeam X-ray photoelectron spectroscopy and scanning tunnelling microscopy/spectroscopy. We determine a type-II alignment between MoS2 and WSe2 with a valence band offset value of 0.83 eV and a conduction band offset of 0.76 eV. First-principles calculations show that in this heterostructure with dissimilar chalcogen atoms, the electronic structures of WSe2 and MoS2 are well retained in their respective layers due to a weak interlayer coupling. Moreover, a valence band offset of 0.94 eV is obtained from density functional theory, consistent with the experimental determination.

  13. Simultaneous Hosting of Positive and Negative Trions and the Enhanced Direct Band Emission in MoSe2/MoS2 Heterostacked Multilayers.

    Science.gov (United States)

    Kim, Min Su; Seo, Changwon; Kim, Hyun; Lee, Jubok; Luong, Dinh Hoa; Park, Ji-Hoon; Han, Gang Hee; Kim, Jeongyong

    2016-06-28

    Heterostacking of layered transition-metal dichalcogenide (LTMD) monolayers (1Ls) offers a convenient way of designing two-dimensional exciton systems. Here we demonstrate the simultaneous hosting of positive trions and negative trions in heterobilayers made by vertically stacking 1L MoSe2 and 1L MoS2. The charge transfer occurring between the 1Ls of MoSe2 and MoS2 converted the polarity of trions in 1L MoSe2 from negative to positive, resulting in the presence of positive trions in the 1L MoSe2 and negative trions in the 1L MoS2 of the same heterostacked bilayer. Significantly enhanced MoSe2 photoluminescence (PL) in the heterostacked bilayers compared to the PL of 1L MoSe2 alone suggests that, unlike other previously reported heterostacked bilayers, direct band transition of 1L MoSe2 in heterobilayer was enhanced after the vertical heterostacking. Moreover, by inserting hexagonal BN monolayers between 1L MoSe2 and 1L MoS2, we were able to adjust the charge transfer to maximize the MoSe2 PL of the heteromultilayers and have achieved a 9-fold increase of the PL emission. The enhanced optical properties of our heterostacked LTMDs suggest the exciting possibility of designing LTMD structures that exploit the superior optical properties of 1L LTMDs.

  14. Chern insulators without band inversion in Mo S2 monolayers with 3 d adatoms

    Science.gov (United States)

    Wei, Xinyuan; Zhao, Bao; Zhang, Jiayong; Xue, Yang; Li, Yun; Yang, Zhongqin

    2017-02-01

    Electronic and topological properties of Mo S2 monolayers endowed with 3 d transition metal (TM) adatoms (V-Fe) are explored by using ab initio methods and k .p models. Without the consideration of the Hubbard U interaction, the V, Cr, and Fe adatoms tend to locate on the top of the Mo atoms, while the most stable site for the Mn atom is at the hollow position of the Mo-S hexagon. After the Hubbard U is applied, the most stable sites of all the systems become the top of the Mo atoms. Chern insulators without band inversion are achieved in these systems. The V and Fe adsorption systems are the best candidates to produce the topological states. The k .p model calculations indicate that these topological states are determined by the TM magnetism, the C3 v crystal field from the Mo S2 substrate, and the TM atomic spin-orbit coupling (SOC). The special two-meron pseudospin texture is found to contribute to the topology. The apparent difference between the Berry curvatures for the V and Fe adsorption systems is also explored. Our results widen the understanding of the Chern insulators and are helpful for the applications of the Mo S2 monolayers in the future electronics and spintronics.

  15. First principles study and empirical parametrization of twisted bilayer MoS2 based on band-unfolding

    Science.gov (United States)

    Tan, Yaohua; Chen, Fan W.; Ghosh, Avik W.

    2016-09-01

    We explore the band structure and ballistic electron transport in twisted bilayer MoS2 using the density functional theory. The sphagetti like bands are unfolded to generate band structures in the primitive unit cell of the original 2H MoS2 bilayer and projected onto the original bands of an individual layer. The corresponding twist angle dependent bandedges are extracted from the unfolded band structures. Based on a comparison within the same primitive unit cell, an efficient two band effective mass model for indirect ΓV and ΛC valleys is created and parametrized by fitting to the unfolded band structures. With the two band effective mass model, we calculate transport properties—specifically, the ballistic transmission in arbitrarily twisted bilayer MoS2 .

  16. Band engineering of the MoS2/stanene heterostructure: strain and electrostatic gating

    Science.gov (United States)

    Xiong, Wenqi; Xia, Congxin; Du, Juan; Wang, Tianxing; Peng, Yuting; Wei, Zhongming; Li, Jingbo

    2017-05-01

    In a fast developing field, it has been found that van der Waals heterostructures can overcome the weakness of single two-dimensional layered materials and extend their electronic and optoelectronic applications. Through first-principles methods, the studied MoS2/stanene heterostructure preserves high-speed carrier characteristics and opens the direct band gap. Simultaneously, the band alignment shows that the electrons transfer from stanene to MoS2, which forms an internal electric field. As an effective strategy, the out-of-plane strain remarkably changes the band gaps of the heterostructure and enhances its carrier concentration. In addition, the combined effects of the internal and external electric fields can further open the band gaps and induce a direct-to-indirect gap transition in the heterostructure. More interestingly, when the external electric field is equal to the reverse internal one, the heterostructure regains a Dirac cone. Our results show that the MoS2/stanene heterostructure has potential applications in high-speed optoelectronic devices.

  17. Chemical Vapor Deposition of Monolayer Mo(1-x)W(x)S2 Crystals with Tunable Band Gaps.

    Science.gov (United States)

    Wang, Ziqian; Liu, Pan; Ito, Yoshikazu; Ning, Shoucong; Tan, Yongwen; Fujita, Takeshi; Hirata, Akihiko; Chen, Mingwei

    2016-02-22

    Band gap engineering of monolayer transition metal dichalcogenides, such as MoS2 and WS2, is essential for the applications of the two-dimensional (2D) crystals in electronic and optoelectronic devices. Although it is known that chemical mixture can evidently change the band gaps of alloyed Mo(1-x)W(x)S2 crystals, the successful growth of Mo(1-x)W(x)S2 monolayers with tunable Mo/W ratios has not been realized by conventional chemical vapor deposition. Herein, we developed a low-pressure chemical vapor deposition (LP-CVD) method to grow monolayer Mo(1-x)W(x)S2 (x = 0-1) 2D crystals with a wide range of Mo/W ratios. Raman spectroscopy and high-resolution transmission electron microscopy demonstrate the homogeneous mixture of Mo and W in the 2D alloys. Photoluminescence measurements show that the optical band gaps of the monolayer Mo(1-x)W(x)S2 crystals strongly depend on the Mo/W ratios and continuously tunable band gap can be achieved by controlling the W or Mo portion by the LP-CVD.

  18. Optical Properties and Band Gap of Single- and Few-Layer MoTe2 Crystals

    Science.gov (United States)

    Aslan, Ozgur Burak; Ruppert, Claudia; Heinz, Tony

    2015-03-01

    Single- and few-layer crystals of exfoliated MoTe2 have been characterized spectroscopically by photoluminescence, Raman scattering, and optical absorption measurements. We find that MoTe2 in the monolayer limit displays strong photoluminescence. On the basis of complementary optical absorption results, we conclude that monolayer MoTe2 is a direct-gap semiconductor with an optical band gap of 1.10 eV. This new monolayer material extends the spectral range of atomically thin direct-gap materials from the visible to the near-infrared. Supported by the NSF through Grant DMR-1124894 for sample preparation and characterization by the O?ce of Naval Research for analysis. C.R. acknowledges support from the Alexander von Humboldt Foundation.

  19. First principles study and empirical parametrization of twisted bilayer MoS2 based on band-unfolding

    CERN Document Server

    Tan, Yaohua; Ghosh, Avik

    2016-01-01

    We explore the band structure and ballistic electron transport in twisted bilayer $\\textrm{MoS}_2$ using Density Functional Theory (DFT). The sphagetti like bands are unfolded to generate band structures in the primitive unit cell of the original un-twisted $\\textrm{MoS}_2$ bilayer and projected onto an individual layer. The corresponding twist angle dependent indirect bandedges are extracted from the unfolded band structures. Based on a comparison within the same primitive unit cell, an efficient two band effective mass model for indirect conduction and valence valleys is created and parameterized by fitting the unfolded band structures. With the two band effective mass model, transport properties - specifically, we calculate the ballistic transmission in arbitrarily twisted bilayer $\\textrm{MoS}_2$.

  20. Giant Rashba-type splitting in molybdenum-driven bands of MoS2/Bi (111 ) heterostructure

    Science.gov (United States)

    Lee, Kyuhwan; Yun, Won Seok; Lee, J. D.

    2015-03-01

    We investigate the electronic band structure of the MoS2/Bi (111 ) heterostructure, for which the supercell calculation is performed due to the lattice mismatch between two structures but the effective primitive cell is recovered by using the band unfolding technique. It is found that the strong molybdenum-bismuth band hybridization together with a generation of the interfacial dipole field induces the giant Rashba-type splitting accompanying the proper spin topology in molybdenum-driven bands at the Γ point. Similar splittings are also found in the heterostructure with other transition-metal dichalcogenides, i.e., with MoSe2,WS2, and WSe2.

  1. A model for the direct-to-indirect band-gap transition in monolayer MoSe2 under strain

    Indian Academy of Sciences (India)

    Ruma Das; Priya Mahadevan

    2015-06-01

    A monolayer of MoSe2 is found to be a direct band-gap semiconductor. We show, within ab-initio electronic structure calculations, that a modest biaxial tensile strain of 3% can drive it into an indirect band-gap semiconductor with the valence band maximum (VBM) shifting from point to point. An analysis of the charge density reveals that while Mo–Mo interactions contribute to the VBM at 0% strain, Mo–Se interactions contribute to the highest occupied band at point. A scaling of the hopping interaction strengths within an appropriate tight binding model can capture the transition.

  2. S-band Q-switched fiber laser using MoSe2 saturable absorber

    Science.gov (United States)

    Ahmad, H.; Ismail, M. A.; Sathiyan, S.; Reduan, S. A.; Ruslan, N. E.; Lee, C. S. J.; Zulkifli, M. Z.; Thambiratnam, K.; Ismail, M. F.; Harun, S. W.

    2017-01-01

    A passively Q-switched S-band fiber laser using Molybdenum Diselenide (MoSe2) saturable absorber (SA) is proposed and demonstrated. The SA is fabricated by depositing MoSe2 onto two fiber ferrules using the drop-cast method before heating and connecting the two fiber ferrules to form the SA. The passively Q-switched fiber laser designed using the MoSe2 SA has an operational range of 1491.0-1502.0 nm. The output pulse train has a pulse-width ranging from 2.0 μs to 1.0 μs and corresponding repetition rate of between 34.5 kHz and 90 kHz with increasing pump powers, as well as a signal-to-noise of about 35.97 dB. The peak performance of the proposed laser is between 1480.0 and 1490.0 nm, corresponding to the first peak gain region with the S-band.

  3. Band Gap Modulation of Bilayer MoS2 Under Strain Engineering and Electric Field: A Density Functional Theory

    Science.gov (United States)

    Nguyen, Chuong V.; Hieu, Nguyen N.; Ilyasov, Victor V.

    2016-08-01

    In this work, we investigate band-gap tuning in bilayer MoS2 by an external electric field and by applied biaxial strain. Our calculations show that the band gaps of bilayer MoS2 can be tuned by the perpendicular electric field or biaxial strain. The band gaps of bilayer MoS2 decrease with increasing applied electric field or biaxial strain. When the electric field was introduced, electronic levels are split due to the separation of the valence sub-band and the conduction sub-band states. Our calculations also show that the change in the band gap of bilayer MoS2 is due to the separation of electronic levels by electric field via the Stark effect. At the electric field E_{Field} = 5.5 V/nm or biaxial strain ɛ = 15%, bilayer MoS2 becomes metallic. The semiconductor-metal phase transition in bilayer MoS2 plays an important role in its application for nanodevices.

  4. Electric field modulation of the band structure in MoS2/WS2 van der waals heterostructure

    Science.gov (United States)

    Li, Wei; Wang, Tianxing; Dai, Xianqi; Wang, Xiaolong; Zhai, Caiyun; Ma, Yaqiang; Chang, Shanshan; Tang, Yanan

    2017-01-01

    Using density functional theory calculations, we investigate the bandstructure of MoS2/WS2 van der waals heterostructure by applying external electric field perpendicular to the layers. It is demonstrated that the MoS2/WS2 is a type-II heterostructure, and therefore the electrons and holes are spatially separated. The band gap of MoS2/WS2 heterostructure continuously decreases with increasing external electric field, eventually a transition from semiconductor to metal is observed. Applying external electric field along +z direction and -z directions has different effects on the band gap due to the intrinsic spontaneous polarization in MoS2/WS2 heterostructure. The calculated result indicates that the band inversion in MoS2/WS2 heterostructure can be induced by changing the strength of the external electric field. The external electric field can significantly tune the band offsets almost linearly and modify the band alignment between MoS2 and WS2. The present study would open a new avenue for application of such transition-metal dichalcogenides heterostructures in future nano- and optoelectronics.

  5. Interfacial Properties of Monolayer and Bilayer MoS2 Contacts with Metals: Beyond the Energy Band Calculations.

    Science.gov (United States)

    Zhong, Hongxia; Quhe, Ruge; Wang, Yangyang; Ni, Zeyuan; Ye, Meng; Song, Zhigang; Pan, Yuanyuan; Yang, Jinbo; Yang, Li; Lei, Ming; Shi, Junjie; Lu, Jing

    2016-01-01

    Although many prototype devices based on two-dimensional (2D) MoS2 have been fabricated and wafer scale growth of 2D MoS2 has been realized, the fundamental nature of 2D MoS2-metal contacts has not been well understood yet. We provide a comprehensive ab initio study of the interfacial properties of a series of monolayer (ML) and bilayer (BL) MoS2-metal contacts (metal = Sc, Ti, Ag, Pt, Ni, and Au). A comparison between the calculated and observed Schottky barrier heights (SBHs) suggests that many-electron effects are strongly suppressed in channel 2D MoS2 due to a charge transfer. The extensively adopted energy band calculation scheme fails to reproduce the observed SBHs in 2D MoS2-Sc interface. By contrast, an ab initio quantum transport device simulation better reproduces the observed SBH in 2D MoS2-Sc interface and highlights the importance of a higher level theoretical approach beyond the energy band calculation in the interface study. BL MoS2-metal contacts generally have a reduced SBH than ML MoS2-metal contacts due to the interlayer coupling and thus have a higher electron injection efficiency.

  6. Effects of interlayer polarization field on the band structures of the WS2/MoS2 and WSe2/MoSe2 heterostructures

    Science.gov (United States)

    Zhu, Huili; Zhou, Changjie; Wu, Yaping; Lin, Wei; Yang, Weihuang; Cheng, Zejie; Cai, Xiaomei

    2017-07-01

    The mechanisms of interaction between the layers of transition metal dichalcogenide (TMD) heterostructures, i.e., WS2/MoS2 and WSe2/MoSe2, were investigated based on density functional theory calculations to deepen the understanding of TMD-based electronic devices. Based on the evolution of the energies of the states at the high-symmetric points (KC1, KV2, ΓV2, KC2, KV1, and ΓV1) and the distributions of the differential charge densities, two interaction mechanisms, interlayer orbital coupling and interlayer polarization field, were found to be operative at the interface of the investigated TMD/TMD systems. Due to the interlayer polarization effect, two energetically close band-edge states at the KC1 and KC2 points or at the KV2 and KV1 points become closer with decreasing interlayer distance. Therefore, the two interaction mechanisms exert opposite effects on the band structures of the investigated TMD/TMD systems. Interlayer orbital coupling tends to split two energetically close band-edge states, whereas the interlayer polarization field tends to bring two energetically close band-edge states closer together. Thus, the observation of the interlayer polarization field in this calculation completes the explanation of the influence of the interlayer interaction in the WS2/MoS2 and WSe2/MoSe2 heterostructures and can be helpful for evaluating the performance of TMD-based electronic devices.

  7. MoS2-WSe2 Hetero Bilayer: Possibility of Mechanical Strain Induced Band Gap Engineering

    Science.gov (United States)

    Sharma, Munish; Kumar, Ashok; Ahluwalia, P. K.

    2014-03-01

    The tunability of band gap in two-dimensional (2D) hetero-bilayers of MoS2-WSe2 with applied mechanical strains (in-plane and out-of-plane) in two different types of stackings (AA and AB) have been investigated in the framework of density functional theory (DFT). The in-plane biaxial tensile strain is found to reduce electronic band gap monotonically and rendered considered bilayer into metal at 6% of applied strain. The transition pressure required for complete semiconductor-to-metal transition is found to be of 7.89 GPa while tensile strength of the reported hetero-bilayer has been calculated 10 GPa at 25% strain. In case of vertical compression strain, 16 GPa pressure has been calculated for complete semiconductor-to-metal transition. The band-gap deformation potentials and effective masses (electron and hole) have been found to posses strong dependence on the type of applied strain. Such band gap engineering in controlled manner (internal control by composition and external control by applied strain) makes the considered hetero-bilayer as a strong candidate for the application in variety of nano scale devices.

  8. Behavior of molecules on interstellar grains - Application of the Langevin equation and iterative extended Hueckel

    Science.gov (United States)

    Aronowitz, S.; Chang, S.

    1980-01-01

    The Langevin equation was used to explore an adsorbate desorption mechanism. Calculations were performed using iterative extended Hueckel on a silica model site with various small adsorbates, e.g., H, CH, OH, NO, CO. It was found that barriers to free traversal from one site to another are substantial (about 3-10 eV). A bootstrap desorption mechanism for some molecules in the process of forming at a site also became apparent from the calculations. The desorption mechanisms appear to be somewhat balanced by a counterforce - the attraction of sites for the newly desorbed molecule. The order of attraction to a silica grain site for the diatomic molecules considered was OH greater than CH greater than CO greater than NO, when these entities were sufficiently distant. The nature of the silica grain and that of the 'cold' desorption mechanism, when considered together, suggest that the abundance of very small grains might be less common than anticipated.

  9. Inter-Layer Coupling Induced Valence Band Edge Shift in Mono- to Few-Layer MoS2

    Science.gov (United States)

    Trainer, Daniel J.; Putilov, Aleksei V.; Di Giorgio, Cinzia; Saari, Timo; Wang, Baokai; Wolak, Mattheus; Chandrasena, Ravini U.; Lane, Christopher; Chang, Tay-Rong; Jeng, Horng-Tay; Lin, Hsin; Kronast, Florian; Gray, Alexander X.; Xi, Xiaoxing X.; Nieminen, Jouko; Bansil, Arun; Iavarone, Maria

    2017-01-01

    Recent progress in the synthesis of monolayer MoS2, a two-dimensional direct band-gap semiconductor, is paving new pathways toward atomically thin electronics. Despite the large amount of literature, fundamental gaps remain in understanding electronic properties at the nanoscale. Here, we report a study of highly crystalline islands of MoS2 grown via a refined chemical vapor deposition synthesis technique. Using high resolution scanning tunneling microscopy and spectroscopy (STM/STS), photoemission electron microscopy/spectroscopy (PEEM) and μ-ARPES we investigate the electronic properties of MoS2 as a function of the number of layers at the nanoscale and show in-depth how the band gap is affected by a shift of the valence band edge as a function of the layer number. Green’s function based electronic structure calculations were carried out in order to shed light on the mechanism underlying the observed bandgap reduction with increasing thickness, and the role of the interfacial Sulphur atoms is clarified. Our study, which gives new insight into the variation of electronic properties of MoS2 films with thickness bears directly on junction properties of MoS2, and thus impacts electronics application of MoS2. PMID:28084465

  10. Edge effects on band gap energy in bilayer 2H-MoS{sub 2} under uniaxial strain

    Energy Technology Data Exchange (ETDEWEB)

    Dong, Liang; Wang, Jin; Dongare, Avinash M., E-mail: dongare@uconn.edu [Department of Materials Science and Engineering and Institute of Materials Science, University of Connecticut, Storrs, Connecticut 06269 (United States); Namburu, Raju [Computational and Information Sciences Directorate, U.S. Army Research Laboratory, Aberdeen Proving Ground, Maryland 21005 (United States); O' Regan, Terrance P.; Dubey, Madan [Sensors and Electron Devices Directorate, U.S. Army Research Laboratory, Adelphi, Maryland 20783 (United States)

    2015-06-28

    The potential of ultrathin MoS{sub 2} nanostructures for applications in electronic and optoelectronic devices requires a fundamental understanding in their electronic structure as a function of strain. Previous experimental and theoretical studies assume that an identical strain and/or stress state is always maintained in the top and bottom layers of a bilayer MoS{sub 2} film. In this study, a bilayer MoS{sub 2} supercell is constructed differently from the prototypical unit cell in order to investigate the layer-dependent electronic band gap energy in a bilayer MoS{sub 2} film under uniaxial mechanical deformations. The supercell contains an MoS{sub 2} bottom layer and a relatively narrower top layer (nanoribbon with free edges) as a simplified model to simulate the as-grown bilayer MoS{sub 2} flakes with free edges observed experimentally. Our results show that the two layers have different band gap energies under a tensile uniaxial strain, although they remain mutually interacting by van der Waals interactions. The deviation in their band gap energies grows from 0 to 0.42 eV as the uniaxial strain increases from 0% to 6% under both uniaxial strain and stress conditions. The deviation, however, disappears if a compressive uniaxial strain is applied. These results demonstrate that tensile uniaxial strains applied to bilayer MoS{sub 2} films can result in distinct band gap energies in the bilayer structures. Such variations need to be accounted for when analyzing strain effects on electronic properties of bilayer or multilayered 2D materials using experimental methods or in continuum models.

  11. Narrow band gap and visible light-driven photocatalysis of V-doped Bi6Mo2O15 nanoparticles

    Science.gov (United States)

    Xu, Jian; Qin, Chuanxiang; Huang, Yanlin; Wang, Yaorong; Qin, Lin; Seo, Hyo Jin

    2017-02-01

    Pure and V5+-doped Bi6Mo2O15 (3Bi2O3·2MoO3) photocatalysts were synthesized through electrospinning, followed by low-temperature heat treatment. The samples developed into nanoparticles with an average size of approximately 50 nm. The crystalline phases were verified via X-ray powder diffraction measurements (XRD). The surface properties of the photocatalysts were studied by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS) analyses. The UV-vis spectra showed that V doping in Bi6Mo2O15 shifted the optical absorption from the UV region to the visible-light wavelength region. The energy of the band gap of Bi6Mo2O15 was reduced by V doping in the lattices. The photocatalytic activities of the pure and V-doped Bi6Mo2O15 were tested through photodegradation of rhodamine B (RhB) dye solutions under visible light irradiation. Results showed that 20 mol% V-doped Bi6Mo2O15 achieved efficient photocatalytic ability. RhB could be degraded by V-doped Bi6Mo2O15 in 2 h. The photocatalytic activities and mechanisms were discussed according to the characteristics of the crystal structure and the results of EIS and XPS measurements.

  12. Indirect Band Gap Emission by Hot Electron Injection in Metal/MoS2 and Metal/WSe2 Heterojunctions

    Science.gov (United States)

    Li, Zhen; Ezhilarasu, Goutham; Chatzakis, Ioannis; Dhall, Rohan; Chen, Chun-Chung; Cronin, Stephen

    Transition metal dichalcogenides (TMDCs), such as MoS2 and WSe2, are free of dangling bonds, therefore make more `ideal' Schottky junctions than bulk semiconductors, which produce recombination centers at the interface with metals, inhibiting charge transfer. Here, we observe a more than 10X enhancement in the indirect band gap PL of TMDCs deposited on various metals, while the direct band gap emission remains unchanged. We believe the main mechanism of light emission arises from photoexcited hot electrons in the metal that are injected into the conduction band of MoS2 and WSe2, and subsequently recombine radiatively with minority holes. Since the conduction band at the K-point is 0.5eV higher than at the Σ-point, a lower Schottky barrier of the Σ-point band makes electron injection more favorable. Also, the Σ band consists of the sulfur pz orbital, which overlaps more significantly with the electron wavefunctions in the metal. This enhancement only occurs for thick flakes, and is absent in monolayer and few-layer flakes. Here, the flake thickness must exceed the depletion width of the Schottky junction, in order for efficient radiative recombination to occur in the TMDC. The intensity of this indirect peak decreases at low temperatures. Reference: DOI: 10.1021/acs.nanolett.5b00885

  13. Observation of monolayer valence band spin-orbit effect and induced quantum well states in MoX2

    Science.gov (United States)

    Alidoust, Nasser; Bian, Guang; Xu, Su-Yang; Sankar, Raman; Neupane, Madhab; Liu, Chang; Belopolski, Ilya; Qu, Dong-Xia; Denlinger, Jonathan D.; Chou, Fang-Cheng; Hasan, M. Zahid

    2014-08-01

    Transition metal dichalcogenides transition metal dichalcogenides have attracted much attention recently due to their potential applications in spintronics and photonics because of the indirect to direct band gap transition and the emergence of the spin-valley coupling phenomenon upon moving from the bulk to monolayer limit. Here, we report high-resolution angle-resolved photoemission spectroscopy on MoSe2 single crystals and monolayer films of MoS2 grown on highly ordered pyrolytic graphite substrate. Our experimental results resolve the Fermi surface trigonal warping of bulk MoSe2, and provide evidence for the critically important spin-orbit split valence bands of monolayer MoS2. Moreover, we systematically image the formation of quantum well states on the surfaces of these materials, and present a theoretical model to account for these experimental observations. Our findings provide important insights into future applications of transition metal dichalcogenides in nanoelectronics, spintronics and photonics devices as they critically depend on the spin-orbit physics of these materials.

  14. Band-gap engineering of the h-BN/MoS2/h-BN sandwich heterostructure under an external electric field

    Science.gov (United States)

    Huang, Zongyu; Qi, Xiang; Yang, Hong; He, Chaoyu; Wei, Xiaolin; Peng, Xiangyang; Zhong, Jianxin

    2015-05-01

    Based on first-principles calculations in the framework of van der Waals density functional theory, we investigate the structural, electronic properties and band-gap tuning of the h-BN/MoS2/h-BN sandwich heterostructure under an external electric field. We find that, different from the suspended monolayer MoS2 with a direct band-gap, h-BN/MoS2/h-BN has an indirect band-gap. Particular attention has been focused on the engineering of the band-gap of the h-BN/MoS2/h-BN heterostructure via application of an external electric field. With the increase of electric field, the band-gap of the h-BN/MoS2/h-BN heterostructure undergoes an indirect-to-direct band-gap transition. Once the electric field intensity is larger than 0.1 V Å-1, the gap value of direct band-gap shrinks almost linearly with the field-strength, which indicates that the h-BN/MoS2/h-BN heterostructure is a viable candidate for optoelectronic applications.

  15. In-situ growth of HfO2 on clean 2H-MoS2 surface: Growth mode, interface reactions and energy band alignment

    Science.gov (United States)

    Chen, Chang Pang; Ong, Bin Leong; Ong, Sheau Wei; Ong, Weijie; Tan, Hui Ru; Chai, Jian Wei; Zhang, Zheng; Wang, Shi Jie; Pan, Ji Sheng; Harrison, Leslie John; Kang, Hway Chuan; Tok, Eng Soon

    2017-10-01

    Room temperature growth of HfO2 thin film on clean 2H-MoS2 via plasma-sputtering of Hf-metal target in an argon/oxygen environment was studied in-situ using x-ray photoelectron spectroscopy (XPS). The deposited film was observed to grow akin to a layer-by-layer growth mode. At the onset of growth, a mixture of sulfate- and sulfite-like species (SOx2- where x = 3, 4), and molybdenum trioxide (MoO3), are formed at the HfO2/MoS2 interface. An initial decrease in binding energies for both Mo 3d and S 2p core-levels of the MoS2 substrate by 0.4 eV was also observed. Their binding energies, however, did not change further with increasing HfO2 thickness. There was no observable change in the Hf4f core-level binding energy throughout the deposition process. With increasing HfO2 deposition, MoO3 becomes buried at the interface while SOx2- was observed to be present in the film. The shift of 0.4 eV for both Mo 3d and S 2p core-levels of the MoS2 substrate can be attributed to a charge transfer from the substrate to the MoO3/SOx2--like interface layer. Consequently, the Type I heterojunction valence band offset (conduction band offset) becomes 1.7 eV (2.9 eV) instead of 1.3 eV (3.3 eV) expected from considering the bulk HfO2 and MoS2 valence band offset (conduction band offset). The formation of these states and its influence on band offsets will need to be considered in their device applications.

  16. Interlayer Excitons and Band Alignment in MoS2/hBN/WSe2 van der Waals Heterostructures

    DEFF Research Database (Denmark)

    Latini, Simone; Winther, Kirsten Trøstrup; Olsen, Thomas

    2017-01-01

    van der Waals heterostructures (vdWH) are ideal systems for exploring light-matter interactions at the atomic scale. In particular, structures with a type-II band alignment can yield detailed insight into carrier-photon conversion processes, which are central to, for example, solar cells and light......-emitting diodes. An important first step in describing such processes is to obtain the energies of the interlayer exciton states existing at the interface. Here we present a general first-principles method to compute the electronic quasi-particle (QP) band structure and excitonic binding energies...... of bilayer MoS2/WSe2 with and without intercalated hBN layers, finding excellent agreement with experimental photoluminescence spectra. A comparison to density functional theory calculations demonstrates the crucial role of self-energy and electron-hole interaction effects....

  17. Competition between Band Filling and Steric Effect in Ordered Double Perovskites Sr2-xLaxMnMoO6

    Institute of Scientific and Technical Information of China (English)

    2006-01-01

    The ordered double perovskites, Sr2-xLaxMnMoO6, were prepared by sol-gel reaction. Structural, magnetic, and electrical properties were investigated for a series of ordered double perovskites Sr2-xLaxMnMoO6 (0≤x≤1). The compounds have a monoclinic structure (space group P21/n) and the cell volume expands monotonically with La doping. The TC and the magnetic moment rise and the cusp-like transition temperature below which the magnetic frustration occurs shifts to high temperature as x increases. With La doping, electrical resistivity of Sr2-xLaxMnMoO6 decreases only at low doping levels (x≤0.2); while at high doping levels (0.8≤x≤1), electrical resistivity tends to increase greatly. The results suggest that the competition between band filling effect and steric effect coexists in the whole doping range, and the formation of ferrimagnetic interactions is not simply at the expense of antiferromagnetic interactions.

  18. Layer dependence of the electronic band alignment of few-layer Mo S2 on Si O2 measured using photoemission electron microscopy

    Science.gov (United States)

    Berg, Morgann; Keyshar, Kunttal; Bilgin, Ismail; Liu, Fangze; Yamaguchi, Hisato; Vajtai, Robert; Chan, Calvin; Gupta, Gautam; Kar, Swastik; Ajayan, Pulickel; Ohta, Taisuke; Mohite, Aditya D.

    2017-06-01

    Tailoring band alignment layer-by-layer using heterojunctions of two-dimensional (2D) semiconductors is an attractive prospect for producing next-generation electronic and optoelectronic devices that are ultrathin, flexible, and efficient. The 2D layers of transition metal dichalcogenides (TMDs) in laboratory devices have already shown favorable characteristics for electronic and optoelectronic applications. Despite these strides, a systematic understanding of how band alignment evolves from monolayer to multilayer structures is still lacking in experimental studies, which hinders development of novel devices based on TMDs. Here, we report on the local band alignment of monolayer, bilayer, and trilayer Mo S2 on a 285-nm-thick Si O2 substrate using an approach to probe the occupied electronic states based on photoemission electron microscopy and deep-ultraviolet light. Local measurements of the vacuum level and the valence band edge at the Brillouin zone center show that the addition of layers to monolayer Mo S2 increases the relative work function and pushes the valence band edge toward the vacuum level. We also deduced n -type doping of few-layer Mo S2 and type-I band alignment across monolayer-to-bilayer and bilayer-to-trilayer lateral junctions. Conducted in isolation from environmental effects owing to the vacuum condition of the measurement and an insulating Si O2 substrate, this study shows a metrology to uncover electronic properties intrinsic to Mo S2 semiconducting layers and emerging 2D crystals alike.

  19. XPS study of the band alignment at ITO/oxide (n-type MoO{sub 3} or p-type NiO) interface

    Energy Technology Data Exchange (ETDEWEB)

    Bernede, J.C. [MOLTECH Anjou, UMR 6200, Universite de Nantes (France); Houari, S.; Khelil, A. [Universite d& #x27; Oran, LPCM2E, Oran Es-Senia (Algeria); Nguyen, D.; Jouan, P.Y.; Mokrani, A.; Cattin, L. [Institut J. Rouxel (IMN), UMR 6502, Universite de Nantes (France); Predeep, P. [Labaratory for Unconventional Electronics and Photonics, Department of Physics, National Institute of Technology, Kerala (India)

    2012-07-15

    While they have different electronic properties n-type MoO{sub 3} and p-type NiO are very efficient as buffer layers between the ITO anode and the organic electron donor in organic photovoltaic cells. While it is admitted that MoO{sub 3} is n-type, its band structure is still under study. Here, the band alignment at the interface of an ITO/MoO{sub 3} heterojunction is studied by X-ray photoelectron spectroscopy (XPS). The same study is realized on the structure ITO/NiO, NiO being a p-type semiconductor. The measurements have been performed on samples obtained under the same experimental conditions as those used to achieve organic photovoltaic cells. The MoO{sub 3} (NiO) upper layer was 3 nm thick. The semidirect XPS technique used to measure the band offsets allows us to estimate the band discontinuities at the interface ITO/MoO{sub 3}: {Delta}E{sub v} = 0.50 eV and {Delta}E{sub c} = 0.90 eV, while at the interface ITO/NiO we have {Delta}E{sub v} = -2.10 eV and {Delta}E{sub c} = -1.90 eV. Therefore, n-type MoO{sub 3} and p-type NiO, which are both very efficient anode buffer layers (ABLs), exhibit different band structure at the contact with ITO. However, the measurement, by means of a Kelvin probe, of the work functions of the structures ITO/NiO and ITO/MoO{sub 3}, shows that they are close and significantly higher than that of ITO alone. (Copyright copyright 2012 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  20. Negative thermal expansion and broad band photoluminescence in a novel material of ZrScMo2VO12

    Science.gov (United States)

    Ge, Xianghong; Mao, Yanchao; Liu, Xiansheng; Cheng, Yongguang; Yuan, Baohe; Chao, Mingju; Liang, Erjun

    2016-04-01

    In this paper, we present a novel material with the formula of ZrScMo2VO12 for the first time. It was demonstrated that this material exhibits not only excellent negative thermal expansion (NTE) property over a wide temperature range (at least from 150 to 823 K), but also very intense photoluminescence covering the entire visible region. Structure analysis shows that ZrScMo2VO12 has an orthorhombic structure with the space group Pbcn (No. 60) at room temperature. A phase transition from monoclinic to orthorhombic structure between 70 and 90 K is also revealed. The intense white light emission is tentatively attributed to the n- and p-type like co-doping effect which creates not only the donor- and acceptor-like states in the band gap, but also donor-acceptor pairs and even bound exciton complexes. The excellent NTE property integrated with the intense white-light emission implies a potential application of this material in light emitting diode and other photoelectric devices.

  1. Observing the semiconducting band-gap alignment of MoS{sub 2} layers of different atomic thicknesses using a MoS{sub 2}/SiO{sub 2}/Si heterojunction tunnel diode

    Energy Technology Data Exchange (ETDEWEB)

    Nishiguchi, Katsuhiko, E-mail: nishiguchi.katsuhiko@lab.ntt.co.jp; Yamaguchi, Hiroshi; Fujiwara, Akira [NTT Basic Research Laboratories, 3-1 Morinosato Wakamiya, Atsugi, Kanagawa 243-0198 (Japan); Castellanos-Gomez, Andres; Zant, Herre S. J. van der; Steele, Gary A. [Kavli Institute of Nanoscience, Delft University of Technology, Lorentzweg 1, 2628CJ Delft (Netherlands)

    2015-08-03

    We demonstrate a tunnel diode composed of a vertical MoS{sub 2}/SiO{sub 2}/Si heterostructure. A MoS{sub 2} flake consisting four areas of different thicknesses functions as a gate terminal of a silicon field-effect transistor. A thin gate oxide allows tunneling current to flow between the n-type MoS{sub 2} layers and p-type Si channel. The tunneling-current characteristics show multiple negative differential resistance features, which we interpret as an indication of different conduction-band alignments of the MoS{sub 2} layers of different thicknesses. The presented tunnel device can be also used as a hybrid-heterostructure device combining the advantages of two-dimensional materials with those of silicon transistors.

  2. Type-I band alignment at MoS2/In0.15Al0.85N lattice matched heterojunction and realization of MoS2 quantum well

    KAUST Repository

    Tangi, Malleswarara

    2017-08-31

    The valence and conduction band offsets (VBO and CBO) at the semiconductor heterojunction are crucial parameters to design the active region of contemporary electronic and optoelectronic devices. In this report, to study the band alignment parameters at the In0.15Al0.85N/MoS2 lattice matched heterointerface, large area MoS2 single layers are chemical vapor deposited on molecular beam epitaxial grown In0.15Al0.85N films and vice versa. We grew InAlN having an in-plane lattice parameter closely matching with that of MoS2. We confirm that the grown MoS2 is a single layer from optical and structural analyses using micro-Raman spectroscopy and scanning transmission electron microscopy. The band offset parameters VBO and CBO at the In0.15Al0.85N/MoS2 heterojunction are determined to be 2.08 ± 0.15 and 0.60 ± 0.15 eV, respectively, with type-I band alignment using high-resolution x-ray photoelectron spectroscopy in conjunction with ultraviolet photoelectron spectroscopy. Furthermore, we design a MoS2 quantum well structure by growing an In0.15Al0.85N layer on MoS2/In0.15Al0.85N type-I heterostructure. By reducing the nitrogen plasma power and flow rate for the overgrown In0.15Al0.85N layers, we achieve unaltered structural properties and a reasonable preservation of photoluminescence intensity with a peak width of 70 meV for MoS2 quantum well (QW). The investigation provides a pathway towards realizing large area, air-stable, lattice matched, and eventual high efficiency In0.15Al0.85N/MoS2/In0.15Al0.85N QW-based light emitting devices.

  3. Adjusting band gap and charge transfer of organometallic complex adsorbed on MoS2 monolayer using vertical electric-field: a first-principles investigation

    Science.gov (United States)

    Bui, Viet Q.; Le, Hung M.; Kawazoe, Yoshiyuki; Kim, Yongho

    2017-01-01

    In this paper, we propose the use of benzene (Bz) to cover the active site on top of a transition metal atom (Cr/Mn/Fe) adsorbed on the MoS2 monolayer. Stable configurations of adatom on the MoS2 surface were predicted using first-principles calculations and their electronic, magnetic properties were investigated. In addition, the influence of vertical electric field on the electronic band structures of the systems was carefully examined. Analyzing the adsorption energies of transition metals given by the PBE calculations, we found that the benzene molecule stabilized the binding of Cr and Mn on the MoS2 surface, but destabilized the Fe binding by approximately 33% of adsorption energy. The attachment of benzene caused modifications on the total magnetizations of the Cr-MoS2 and Mn-MoS2 structures. The Bz-Mn@MoS2 structure was found to exhibit half-metallicity with 100% spin polarization at the Fermi level. The influence of various degrees of vertical electric field was shown to produce a tensile stress, which altered the lattice parameters and led to band gap narrowing and dramatic shifts of the Fermi level.

  4. Enhancement of broad-band light absorption in monolayer MoS2 using Ag grating hybrid with distributed Bragg reflector

    Science.gov (United States)

    Cao, Jintao; Wang, Jin; Yang, Guofeng; Lu, Yann; Sun, Rui; Yan, Pengfei; Gao, Shumei

    2017-10-01

    A hybrid novel structure of monolayer MoS2 with Ag nanograting and DBR on Si substrate has been proposed to obtain broad-band absorption response for two-dimensional (2D) materials. It is effective to reduce light loss and reflect the incident light efficiently for monolayer MoS2 absorption with DBR dielectric layers. Moreover, by combining Ag nanograting with DBR structure, the average absorption achieves as high as 59% within broad wavelength ranging from 420 to 700 nm, which is attributed to the plasmonic resonant effect of metal nanostripes. The absorption would be affected by the duty ratio and period of the Ag nanograting, and shows incident angle dependent characteristics, while an average absorption higher than 60% has been obtained at the incident angle around 40°. These results indicate that 2D MoS2 in combination with DBR and metal nanograting have a promising potential applications for optical nano-devices.

  5. Effects of nitrogen plasma treatment on the electrical property and band structure of few-layer MoS{sub 2}

    Energy Technology Data Exchange (ETDEWEB)

    Su, Ting-Hong; Lin, Yow-Jon, E-mail: rzr2390@yahoo.com.tw [Institute of Photonics, National Changhua University of Education, Changhua 500, Taiwan (China)

    2016-01-18

    Few-layer MoS{sub 2} prepared by the chemical vapor deposition method was treated with nitrogen plasma under different radio-frequency (rf) power conditions in order to experimentally study the change in the electrical property. Control of the rf power could change the work function of MoS{sub 2} from 5.40 eV to 5.06 eV. It is shown that the increased rf power leads to the increased (reduced) number of nitrogen (oxygen) atoms, increasing the electron concentration and shifting the Fermi level toward conduction band. The sensitivity of the work function to the rf power provides an opportunity to tune the work function of MoS{sub 2}.

  6. Biaxial crystal α-BaTeMo(2)O(9): theory study of large birefringence and wide-band polarized prisms design.

    Science.gov (United States)

    Gao, Z L; Wu, Q; Liu, X T; Sun, Y X; Tao, X T

    2015-02-23

    α-BaTeMo(2)O(9) is a novel biaxial crystal with wide-band transmittance spectrum. The refractive index dispersion curves and birefringence of the α-BaTeMo(2)O(9) crystal were obtained in spectral range of 0.4~5 μm. The origin of the birefringence for the crystal has been calculated and interpreted on the basis of the crystal structure combined with theoretical studies. The polarized directions and formulations of refractive index of optical waves in biaxial α-BaTeMo(2)O(9) were investigated by solving the refractive index ellipsoid equations. Furthermore, polarized prisms based on the α-BaTeMo(2)O(9) crystal used in spectral ranges of 0.4~2.7 μm and 0.48~4.5 μm were designed and characterized. The extinction ratios of both prisms were determined to be larger than 10000:1, which would satisfy the practical requirements. The impacts on extinction ratio for biaxial and uniaxial crystals were also discussed. To our knowledge, it is the first report about biaxial crystals for the polarized prisms, and the results show that the α-BaTeMo(2)O(9) crystal is a promising material for polarized optical components, especially in the range of 3~5 μm.

  7. Broad-Band Photocurrent Enhancement in MoS2 Layers Directly Grown on Light-Trapping Si Nanocone Arrays.

    Science.gov (United States)

    Cho, Yunae; Cho, Byungjin; Kim, Yonghun; Lee, Jihye; Kim, Eunah; Nguyen, Trang Thi Thu; Lee, Ju Hyun; Yoon, Seokhyun; Kim, Dong-Ho; Choi, Jun-Hyuk; Kim, Dong-Wook

    2017-02-22

    There has been growing research interest in realizing optoelectronic devices based on the two-dimensional atomically thin semiconductor MoS2 owing to its distinct physical properties that set it apart from conventional semiconductors. However, there is little optical absorption in these extremely thin MoS2 layers, which presents an obstacle toward applying them for use in high-efficiency light-absorbing devices. We synthesized trilayers of MoS2 directly on SiO2/Si nanocone (NC) arrays using chemical vapor deposition and investigated their photodetection characteristics. The photoresponsivity of the MoS2/NC structure was much higher than that of the flat counterpart across the whole visible wavelength range (for example, it was almost an order of magnitude higher at λ = 532 nm). Strongly concentrated light near the surface that originated from a Fabry-Perot interference in the SiO2 thin layers and a Mie-like resonance caused by the Si NCs boosted the optical absorption in MoS2. Our work demonstrates that MoS2/NC structures could provide a useful means to realize high-performance optoelectronic devices.

  8. Efficient many-body calculations for two-dimensional materials using exact limits for the screened potential: Band gaps of MoS2, h -BN, and phosphorene

    Science.gov (United States)

    Rasmussen, Filip A.; Schmidt, Per S.; Winther, Kirsten T.; Thygesen, Kristian S.

    2016-10-01

    Calculating the quasiparticle (QP) band structure of two-dimensional (2D) materials within the GW self-energy approximation has proven to be a rather demanding computational task. The main reason is the strong q dependence of the 2D dielectric function around q =0 that calls for a much denser sampling of the Brillouin zone (BZ) than is necessary for similar three-dimensional solids. Here, we use an analytical expression for the small q limit of the 2D response function to perform the BZ integral over the critical region around q =0 . This drastically reduces the requirements on the q -point mesh and implies a significant computational speedup. For example, in the case of monolayer MoS2, convergence of the G0W0 band gap to within ˜0.1 eV is achieved with 12 ×12 q points rather than the 36 ×36 mesh required with discrete BZ sampling techniques. We perform a critical assessment of the band gap of the three prototypical 2D semiconductors, MoS2, h -BN, and phosphorene, including the effect of self-consistency at the GW0 level. The method is implemented in the open source code gpaw.

  9. Band Gap Tuning of h-MoO3 Nanocrystals for Efficient Visible Light Photocatalytic Activity Against Methylene Blue Dye.

    Science.gov (United States)

    Chithambararaj, A; Winston, B; Sanjini, N S; Velmathi, S; Bose, A Chandra

    2015-07-01

    The photocatalytic degradation of methylene blue (MB) dye in aqueous solution was investigated using hexagonal molybdenum oxide (h-MoO3) nanocrystals under visible light irradiation. Chemical precipitation method was utilized to synthesize h-MoO3 and control over the crystal size, shape and distribution were characterized by using HNO3 and HCl as precipitating reagents. The photocatalysts were examined through X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, scanning electron microscopy (SEM) and energy dispersive X-ray spectrum (EDX) for structural, functional, surface morphology and elemental analysis, respectively. The XRD results revealed that the samples were in single phase hexagonal crystal structure. XRD peak broadening analysis was used for crystallite size and strain estimation. The particles were anisotropic in nature and showed one dimensional (1-D) rod structure with hexagonal cross section. Further, the crystal phase stability, optical absorption and emission properties were studied by thermo gravimetric analysis (TGA), diffuse reflectance spectroscopy (DRS) and photoluminescence (PL) measurements, respectively. The photocatalytic results demonstrated that the photocatalytic activity of h-MoO3 synthesized using HCl was improved, in comparison to that of HNO3 utilized h-MoO3 sample.

  10. Observation of spin-polarized bands and domain-dependent Fermi arcs in polar Weyl semimetal MoT e2

    Science.gov (United States)

    Sakano, M.; Bahramy, M. S.; Tsuji, H.; Araya, I.; Ikeura, K.; Sakai, H.; Ishiwata, S.; Yaji, K.; Kuroda, K.; Harasawa, A.; Shin, S.; Ishizaka, K.

    2017-03-01

    We investigate the surface electronic structures of polar 1 T'-MoT e2 , the Weyl semimetal candidate realized through the nonpolar-polar structural phase transition, by utilizing the laser angle-resolved photoemission spectroscopy combined with first-principles calculations. Two kinds of domains with different surface band dispersions are observed from a single-crystalline sample. The spin-resolved measurements further reveal that the spin polarizations of the surface and the bulk-derived states show the different domain dependences, indicating the opposite bulk polarity. For both domains, some segmentlike band features resembling the Fermi arcs are clearly observed. The patterns of the arcs present the marked contrast between the two domains, respectively agreeing well with the slab calculation of (0 0 1) and (0 0 -1) surfaces. The present result strongly suggests that the Fermi arc connects the identical pair of Weyl nodes on one side of the polar crystal surface, whereas it connects between the different pairs of Weyl nodes on the other side.

  11. Observing the semiconducting band-gap alignment of MoS2 layers of different atomic thicknesses using a MoS2/SiO2/Si heterojunction tunnel diode

    NARCIS (Netherlands)

    Nishiguchi, K.; Castellanos-Gomez, A.; Yamaguchi, H.; Fujiwara, A.; Van der Zant, H.S.J.; Steele, G.A.

    2015-01-01

    We demonstrate a tunnel diode composed of a vertical MoS2/SiO2/Si heterostructure. A MoS2 flake consisting four areas of different thicknesses functions as a gate terminal of a silicon field-effect transistor. A thin gate oxide allows tunneling current to flow between the n-type MoS2 layers and p-ty

  12. Chemical bond properties and charge transfer bands of O(2-)-Eu(3+), O(2-)-Mo(6+) and O(2-)-W(6+) in Eu(3+)-doped garnet hosts Ln3M5O12 and ABO4 molybdate and tungstate phosphors.

    Science.gov (United States)

    Liu, Xiaoguang; Li, Ling; Noh, Hyeon Mi; Moon, Byung Kee; Choi, Byung Chun; Jeong, Jung Hyun

    2014-06-21

    Charge transfer (CT) energy from the ligand to the central ions is an important factor in luminescence properties for rare earth doped inorganic phosphors. The dielectric theory of complex crystals was used to calculate chemical bond properties. Combining the photoluminescence and the dielectric theory of complex crystals, the CT bands of O(2-)-Eu(3+), O(2-)-Mo(6+) and O(2-)-W(6+) for Eu(3+)-doped inorganic phosphors have been investigated experimentally and theoretically. Taking Eu(3+)-doped Ln3M5O12 (Ln = Y, Lu and M = Al, Ga), Gd3Ga5O12, MMoO4 (M = Ca, Sr, Ba) and MWO4 (M = Ca, Sr, Ba) as typical phosphors, we investigated the effects of the cation size on the CT bands and chemical bond properties including the bond length (d), the covalency (fc), the bond polarizability (αb) and the environmental factor (he) of O(2-)-Eu(3+), O(2-)-Mo(6+) and O(2-)-W(6+), respectively. For systematic isostructural Ln3M5O12 (Ln = Y, Lu and M = Al, Ga) phosphors, with the increasing M ion radius, the bond length of Ln-O decreases, but fc and αb increase, which is the main reason that the environmental factor increased. For the isostructural MMoO4:Eu, with the increasing M ion radius, the Mo-O bond length increases, but fc and αb decrease, and thus he decreases. However, in the compound system MWO4:Eu (M = Ca, Ba) with the increasing M ion radius, the O-W bond length increases, but fc and αb increase, and thus he increases and the O-W CT energy decreases. Their O(2-)-Eu(3+), O(2-)-Mo(6+) and O(2-)-W(6+) CT bands as well as their full width at half maximum (FWHM) were directly influenced by he. And with the increasing he, CT bands of O-Eu or O-Mo or O-W decrease and their FWHM increases. These results indicate a promising approach for changing the material properties, searching for new Eu(3+) doped molybdate, tungstate or other oxide phosphors and analyzing the experimental result.

  13. Visible-light-driven Cu(II)-(Sr(1-y)Na(y))(Ti(1-x)Mo(x))O3 photocatalysts based on conduction band control and surface ion modification.

    Science.gov (United States)

    Qiu, Xiaoqing; Miyauchi, Masahiro; Yu, Huogen; Irie, Hiroshi; Hashimoto, Kazuhito

    2010-11-03

    Band-gap narrowing is generally considered to be a primary method in the design of visible-light-active photocatalysts because it can decrease the photo threshold to lower energies. However, controlling the valence band by up-shifting the top of the band or inducing localized levels above the band results in quantum efficiencies under visible light much lower than those under UV irradiation (such as those reported for N-doped TiO(2): Science 2001, 293, 269. J. Phys. Chem. B 2003, 107, 5483). Herein, we report a systematic study on a novel, visible-light-driven photocatalyst based on conduction band control and surface ion modification. Cu(II)-(Sr(1-y)Na(y))(Ti(1-x)Mo(x))O(3) photocatalysts were prepared by a soft chemical method in combination with an impregnation technique. It is found that Mo(6+) as well as Na(+) doping in the SrTiO(3) can lower the bottom of the conduction band and effectively extend the absorption edge to the visible light region. The Cu(II) clusters grafted on the surface act as a co-catalyst to efficiently reduce the oxygen molecules, thus consuming the excited electrons. Consequently, photocatalytic decomposition of gaseous 2-propanol into CO(2) is achieved, that is, CH(3)CHOHCH(3) + (9)/(2)O(2) → 3CO(2) + H(2)O. For Cu(II)-(Sr(1-y)Na(y))(Ti(1-x)Mo(x))O(3) at x = 2.0% under visible light irradiation, the maximum CO(2) generation rate can reach 0.148 μmol/h; the quantum efficiency under visible light is calculated to be 14.5%, while it is 10% under UV light irradiation. Our results suggest that high visible light photocatalytic efficiency can be achieved by combining conduction band control and surface ion modification, which provides a new approach for rational design and development of high-performance photocatalysts.

  14. Photonic Band Gap in 1D Multilayers Made by Alternating SiO2 or PMMA with monolayer MoS2 or WS2

    CERN Document Server

    del Valle, Diana Gisell Figueroa; Scotognella, Francesco

    2015-01-01

    Atomically thin molybdenum disulphide (MoS2) and tungsten disulphide (WS2) are very interesting two dimensional materials for optics and electronics. In this work we show the possibility to obtain one-dimensional photonic crystals consisting of low-cost and easy processable materials, as silicon dioxide (SiO2) or poly methyl methacrylate (PMMA), and monolayers of MoS2 or WS2. We have simulated the transmission spectra of the photonic crystals using the transfer matrix method and employing the wavelength dependent refractive indexes of the materials. This study envisages the experimental fabrication of these new types of photonic crystals for photonic and light emission applications.

  15. Efficient many-body calculations for two-dimensional materials using exact limits for the screened potential: Band gaps of MoS2, h-BN, and phosphorene

    DEFF Research Database (Denmark)

    Rasmussen, Filip Anselm; Schmidt, Per Simmendefeldt; Winther, Kirsten Trøstrup;

    2016-01-01

    sampling of the Brillouin zone (BZ) than is necessary for similar three-dimensional solids. Here, we use an analytical expression for the small q limit of the 2D response function to perform the BZ integral over the critical region around q = 0. This drastically reduces the requirements on the q-point mesh...... and implies a significant computational speedup. For example, in the case of monolayer MoS2, convergence of the G0W0 band gap to within similar to 0.1 eV is achieved with 12 x 12 q points rather than the 36 x 36 mesh required with discrete BZ sampling techniques. We perform a critical assessment of the band...

  16. The effects of different possible modes of uniaxial strain on the tunability of electronic and band structures in {MoS}_2 monolayer nanosheet via first-principles density functional theory

    Science.gov (United States)

    Dimple; Jena, Nityasagar; Behere, Shounak Dhananjay; De Sarkar, Abir

    2017-07-01

    Ab-initio density functional theory-based calculations have been performed on monolayer (ML) {MoS}_2 nanosheet to study the variation of its electronic properties with the application of uniaxial tensile and compressive strain along its two non-equivalent lattice directions, namely, the zig-zag and the arm-chair directions. Among all the strain types considered in this study, uniaxial tensile strain applied along the zig-zag direction is found to be the most efficacious, inducing a greater tunability in the band gap over a large energy range (from 1.689 to 0.772 eV corresponding to 0-9% of applied strain), followed by uniaxial tensile strain along arm-chair direction. In contrast, the ML- {MoS}_2 nanosheet is found to be less sensitive to the compressive strain applied uniaxially along both the arm-chair as well as zig-zag directions. Moreover, the charges on Mo and S atoms are not found to undergo considerable changes under the application of uniaxial strain, as the atomic motion along the other direction is free from any constraint.

  17. The effects of different possible modes of uniaxial strain on the tunability of electronic and band structures in $\\rm{MoS_2}$ monolayer nanosheet via first-principles density functional theory

    Indian Academy of Sciences (India)

    DIMPLE; NITYASAGAR JENA; SHOUNAK DHANANJAY BEHERE; ABIR DE SARKAR

    2017-07-01

    $\\it{Ab-initio}$ density functional theory-based calculations have been performed on monolayer (ML) $\\rm{MoS_2}$ nanosheet to study the variation of its electronic properties with the application of uniaxial tensile and compressive strain along its two non-equivalent lattice directions, namely, the zig-zag and the arm-chair directions. Among all the strain types considered in this study, uniaxial tensile strain applied along the zig-zag direction is found to be the most efficacious, inducing a greater tunability in the band gap over a large energy range (from 1.689 to 0.772 eV corresponding to 0–9% of applied strain), followed by uniaxial tensile strain along arm-chair direction. In contrast, the $\\rm{ML–MoS_2}$ nanosheet is found to be less sensitive to the compressive strain applied uniaxially along both the arm-chair as well as zig-zag directions.Moreover, the charges on Mo and S atoms are not found to undergo considerable changes under the application of uniaxial strain, as the atomic motion along the other direction is free from any constraint.

  18. Two-dimensional hybrid layered materials: strain engineering on the band structure of MoS2/WSe2 hetero-multilayers

    Science.gov (United States)

    Gu, Kunming; Yu, Sheng; Eshun, Kwesi; Yuan, Haiwen; Ye, Huixian; Tang, Jiaoning; Ioannou, Dimitris E.; Xiao, Changshi; Wang, Hui; Li, Qiliang

    2017-09-01

    In this paper, we report a comprehensive modeling and simulation study of constructing hybrid layered materials by alternately stacking MoS2 and WSe2 monolayers. Such hybrid MoS2/WSe2 hetero-multilayers exhibited direct bandgap semiconductor characteristics with bandgap energy (E g) in a range of 0.45-0.55 eV at room temperature, very attractive for optoelectronics (wavelength range 2.5-2.75 μm) based on thicker two-dimensional (2D) materials. It was also found that the interlayer distance has a significant impact on the electronic properties of the hetero-multilayers, for example a five orders of magnitude change in the conductance was observed. Three material phases, direct bandgap semiconductor, indirect bandgap semiconductor, and metal were observed in MoS2/WSe2 hetero-multilayers, as the interlayer distance decreased from its relaxed (i.e., equilibrium) value of about 6.73 Å down to 5.50 Å, representing a vertical pressure of about 0.8 GPa for the bilayer and 1.5 GPa for the trilayer. Such new hybrid layered materials are very interesting for future nanoelectronic pressure sensor and nanophotonic applications. This study describes a new approach to explore and engineer the construction and application of tunable 2D semiconductors.

  19. Gamma Vibrational Bands and Chiral Doublet Bands in A≈100 Neutron-rich Nuclei

    Institute of Scientific and Technical Information of China (English)

    ZHU Sheng-jiang; DING Huai-bo; J.H.Hamilton; A.V.Ramayya; CHE Xing-lai; J.K.Hwang; Y.X.Luo; J.O.Rasmussen; K.Li; WANG Jian-guo; XU Qiang; GU Long; YANG Yun-yi; S.Frauendorf; V.Dimitrov

    2009-01-01

    The level structures of neutron-rich ~(105)Mo,~(106)Mo,~(108)Mo and 110Ru nuclei in A≈100 region have been carefully investigated by coincidence measurements of the prompt γ-rays populated in the spontaneous fission of ~(252)Cf with the Gammasphere detector array.In 105Mo,one-phonon K =9/2 and two-phonon K=13/2 γ-vibrational bands have been identified.In ~(108)Mo,one-phonon γ-vibrational band is expanded and two-phonon γ-vibrational band has been identified.Two similar sets of bands in ~(106)Mo and ~(110)Ru are observed to high spins,which have been proposed as the soft chiral γ-vibrational bands.The characteristics for these γ-vibrational bands and chiral doublet bands have been discussed.

  20. Level structure of 89Mo

    Science.gov (United States)

    García-Bermúdez, G.; Cardona, M. A.; Ribas, R. V.; Filevich, A.; Achterberg, E.; Szybisz, L.

    1993-10-01

    The level structure of 89Mo has been studied with the 60Ni(32S,2pn) reaction at 110 MeV beam energy. Mainly two bands of γ rays depopulating states of probable spin-parity values ranging up to (27/2)+ were determined from the excitation function, neutron and γ-γ coincidences, and γ-ray angular distributions. The high-spin states of 89Mo show a scheme very similar to that of the 87Zr isotone. The interpretation of these states in terms of the three neutron-hole configuration (νg9/2)-3 and core-excited states is discussed.

  1. Ultrafast charge transfer between MoTe2 and MoS2 monolayers

    Science.gov (United States)

    Pan, Shudi; Ceballos, Frank; Bellus, Matthew Z.; Zereshki, Peymon; Zhao, Hui

    2017-03-01

    High quality and stable electrical contact between metal and two-dimensional materials, such as transition metal dichalcogenides, is a necessary requirement that has yet to be achieved in order to successfully exploit the advantages that these materials offer to electronics and optoelectronics. MoTe2, owing to its phase changing property, can potentially offer a solution. A recent study demonstrated that metallic phase of MoTe2 connects its semiconducting phase with very low resistance. To utilize this property to connect other two-dimensional materials, it is important to achieve efficient charge transfer between MoTe2 and other semiconducting materials. Using MoS2 as an example, we report ultrafast and efficient charge transfer between MoTe2 and MoS2 monolayers. In the transient absorption measurements, an ultrashort pump pulse is used to selectively excite electrons in MoTe2. The appearance of the excited electrons in the conduction band of MoS2 is monitored by using a probe pulse that is tuned to the resonance of MoS2. We found that electrons transfer to MoS2 on a time scale of at most 0.3 ps. The transferred electrons give rise to a large transient absorption signal at both A-exciton and B-exciton resonances due to the screening effect. We also observed ultrafast transfer of holes from MoS2 to MoTe2. Our results suggest the feasibility of using MoTe2 as a bridge material to connect MoS2 and other transition metal dichalcogenides, and demonstrate a new transition metal dichalcogenide heterostructure involving MoTe2, which extends the spectral range of such structures to infrared.

  2. Electronic properties of MoS2/MoOx interfaces: Implications in Tunnel Field Effect Transistors and Hole Contacts

    Science.gov (United States)

    K. C., Santosh; Longo, Roberto C.; Addou, Rafik; Wallace, Robert M.; Cho, Kyeongjae

    2016-01-01

    In an electronic device based on two dimensional (2D) transitional metal dichalcogenides (TMDs), finding a low resistance metal contact is critical in order to achieve the desired performance. However, due to the unusual Fermi level pinning in metal/2D TMD interface, the performance is limited. Here, we investigate the electronic properties of TMDs and transition metal oxide (TMO) interfaces (MoS2/MoO3) using density functional theory (DFT). Our results demonstrate that, due to the large work function of MoO3 and the relative band alignment with MoS2, together with small energy gap, the MoS2/MoO3 interface is a good candidate for a tunnel field effect (TFET)-type device. Moreover, if the interface is not stoichiometric because of the presence of oxygen vacancies in MoO3, the heterostructure is more suitable for p-type (hole) contacts, exhibiting an Ohmic electrical behavior as experimentally demonstrated for different TMO/TMD interfaces. Our results reveal that the defect state induced by an oxygen vacancy in the MoO3 aligns with the valance band of MoS2, showing an insignificant impact on the band gap of the TMD. This result highlights the role of oxygen vacancies in oxides on facilitating appropriate contacts at the MoS2 and MoOx (x < 3) interface, which consistently explains the available experimental observations. PMID:27666523

  3. The first observation of Mo5+ in the passivation layer of Mo2N

    Institute of Scientific and Technical Information of China (English)

    2000-01-01

    Molybdenum nitride powder with sg of 115 m2·g-1 (passivated) has been prepared by a temperature programmed reaction of MoO3 in H2/N2 mixture. It exhibited high catalytic activity in CO oxidation at low temperature. XPS, EPR and LRS studies have shown the existence of mixed valence states of Mo ions, especially Mo5+ ion (g⊥=1.932, g‖=1.892) observed for the first time, in the passivation layer of molybdenum nitride. A surface superoxide species, O-2(g = 2.001, Raman band 1 124 cm-1), was found to be produced accompanying the transformation of Mo5+/Mo4+ redox pair. Evidence has been given to suggest that this surface superoxide might be responsible for CO oxidation over Mo2N catalyst.

  4. Electronic and dielectric properties of MoS2-MoX2 heterostructures

    Science.gov (United States)

    Sharma, Munish; Jamdagni, Pooja; Kumar, Ashok; Ahluwalia, P. K.

    2015-05-01

    We present a comparative study of electronic and dielectric properties of MoS2-MoX2 heteostructures (where X=S, Se, Te) within the framework of density functional theory (DFT). Electronic band structure, real & imaginary part of dielectric function, electron energy loss spectra and static dielectric constant have been calculated for each system and compared with one another. A systematic decrease/increase in band gap/static dielectric constant is observed as the X changes from S to Te. These results provide a physical basis for the potential applications of these heterostructures in optoelectronic devices.

  5. 应变对单层二硫化钼能带影响的第一性原理研究%The effect of strain on band structure of single-layer MoS2: an ab initio study

    Institute of Scientific and Technical Information of China (English)

    吴木生; 徐波; 刘刚; 欧阳楚英

    2012-01-01

    We study the electronic properties of single-layer MoS2 with biaxial tensile strain by using an ab initio method of plane wave potential technique based on the density function theory. Our results show that a smalL tensile strain (0.5%) will result in the transition from direct to indirect gap for ingle-layer MoS2. With the increase of strain, the feature of the indirect gap can be preserved but the gap decreases linearly. Based on the further analysis of the density of states and the projected charge density for single-layer MoS2, the reason of the change of band structure is revealed.%采用密度泛函理论框架下的第一性原理平面波赝势方法,研究了双轴拉应变下单层二硫化钼晶体的电子结构性质.本文的计算结果表明对单层二硫化钼晶体施加一个很小的应变(0.5%)时,其能带结构由直接带隙转变为间接带隙.随着应变的增加,能带仍然保持间接带隙的特征,且禁带宽度呈现线性下降的趋势.通过对单层二硫化钼晶体态密度和投影电荷密度的进一步分析,揭示了单层二硫化钼晶体能带变化的原因.

  6. The crystal and magnetic structure relationship in Cu(W{sub 1-x}Mo{sub x})O{sub 4} compounds with wolframite-type structure

    Energy Technology Data Exchange (ETDEWEB)

    Ehrenberg, Helmut [Institute for Materials Science, Darmstadt University of Technology, Darmstadt (Germany)]. E-mail: helmut@tu-darmstadt.de; Theissmann, Ralf; Gassenbauer, Yvonne; Knapp, Michael; Wltschek, Gernot; Weitzel, Hans; Fuess, Hartmut [Institute for Materials Science, Darmstadt University of Technology, Darmstadt (Germany); Herrmannsdoerfer, Thilo; Sheptyakov, Denis [Laboratory for Neutron Scattering, ETH Zuerich and Paul Scherrer Institute, Villigen PSI (Switzerland)

    2002-09-16

    The magnetic structures of Cu(W{sub 1-x}Mo{sub x})O{sub 4} compounds with wolframite-type structure at 1.5 K have been determined by neutron powder diffraction for average composition =0.15, 0.25 and 0.35. For =0.15 the magnetic structure is antiferromagnetic with a magnetic unit cell doubled along the a-axis, k-vector=(1/2, 0, 0), i.e. the same magnetic structure as for CuWO{sub 4}. For =0.25 and 0.35 two magnetic structures are observed: one is identical to that for =0.15, while the other is doubled with respect to the c-axis, k-vector=(0, 0, 1/2), i.e. the same magnetic structure as for the high-pressure modification CuMoO{sub 4} III. The coexistence of these two magnetic arrangements is interpreted as reflecting a slightly inhomogeneous contribution of Mo and W in different crystallites together with a sharp transition between the stability ranges of the two types of magnetic structure with respect to x. The specific Mo:W distributions in the grains of the powdered samples were deduced from a profile analysis based on high-resolution synchrotron powder diffraction data. No additional, intermediate magnetic phase with k-vector=(1/2, 1/2, 0) was found in Cu(W{sub 0.75}Mo{sub 0.25})O{sub 4}, in contrast to predictions in the framework of extended Hueckel calculations based on the precise crystal structure. (author)

  7. Properties of Superconducting Mo, Mo2n and Trilayer Mo2n-Mo-Mo2n Thin Films

    Science.gov (United States)

    Barrentine, E. M.; Stevenson, T. R.; Brown, A. D.; Lowitz, A. E.; Noroozian, O.; U-Yen, K.; Eshan, N.; Hsieh, W. T.; Moseley, S. H.; Wollack, E. J.

    2014-01-01

    We present measurements of the properties of thin film superconducting Mo, Mo2N and Mo2N/Mo/Mo2N trilayers of interest for microwave kinetic inductance detector (MKID) applications. Using microwave resonator devices, we investigate the transition temperature, energy gaps, kinetic inductance, and internal quality factors of these materials. We present an Usadel-based interpretation of the trilayer transition temperature as a function of trilayer thicknesses, and a 2-gap interpretation to understand the change in kinetic inductance and internal resonance quality factor (Q) as a function of temperature.

  8. Interlayer Transition and Infrared Photodetection in Atomically Thin Type-II MoTe₂/MoS₂ van der Waals Heterostructures.

    Science.gov (United States)

    Zhang, Kenan; Zhang, Tianning; Cheng, Guanghui; Li, Tianxin; Wang, Shuxia; Wei, Wei; Zhou, Xiaohao; Yu, Weiwei; Sun, Yan; Wang, Peng; Zhang, Dong; Zeng, Changgan; Wang, Xingjun; Hu, Weida; Fan, Hong Jin; Shen, Guozhen; Chen, Xin; Duan, Xiangfeng; Chang, Kai; Dai, Ning

    2016-03-22

    We demonstrate the type-II staggered band alignment in MoTe2/MoS2 van der Waals (vdW) heterostructures and an interlayer optical transition at ∼1.55 μm. The photoinduced charge separation between the MoTe2/MoS2 vdW heterostructure is verified by Kelvin probe force microscopy (KPFM) under illumination, density function theory (DFT) simulations and photoluminescence (PL) spectroscopy. Photoelectrical measurements of MoTe2/MoS2 vdW heterostructures show a distinct photocurrent response in the infrared regime (1550 nm). The creation of type-II vdW heterostructures with strong interlayer coupling could improve our fundamental understanding of the essential physics behind vdW heterostructures and help the design of next-generation infrared optoelectronics.

  9. Location of Trapped Electron Centers in the Bulk of Epitaxial MgO(001) Films Grown on Mo(001) Using in situ W-band Electron Paramagnetic Resonance Spectroscopy.

    Science.gov (United States)

    Cornu, Damien; Rocker, Jan; Gonchar, Anastasia; Risse, Thomas; Freund, Hans-Joachim

    2016-07-01

    We present the first in situ W-band (94-GHz) electron paramagnetic resonance (EPR) study of a trapped electron center in thin MgO(001) films. The improved resolution of the high-field EPR experiments proves that the signal originate from a well-defined species present in the bulk of the films, whose projection of the principal g-tensor components onto the (001) plane are oriented along the [110] direction of the MgO lattice. Based on a comparison between the structural properties of the films, knowledge of the ability of bulk defects to trap electrons, and the properties of the EPR signal, it is possible to propose that the paramagnetic species are located at the origin of a screw dislocation in the bulk of the film.

  10. Chemically induced compaction bands in geomaterials

    Science.gov (United States)

    Stefanou, Ioannis; Sulem, Jean

    2013-04-01

    -sensitive Dilatant Materials." Journal of the Mechanics and Physics of Solids 23.6 (1975): 371-394. [2] I. Vardoulakis and J. Sulem: Bifurcation analysis in geomechanics. Blackie. 1995. [3] J.W. Rudnicki, "Conditions for Compaction and Shear Bands in a Transversely Isotropic Material." International Journal of Solids and Structures 39.13-14 (2002): 3741-3756. [4] L.-B. Hu and T. Hueckel. "Coupled Chemo-mechanics of Intergranular Contact: Toward a Three-scale Model." Computers and Geotechnics 34.4 (2007): 306-327. [5] R. Nova, R. Castellanza, and C. Tamagnini. "A Constitutive Model for Bonded Geomaterials Subject to Mechanical And/or Chemical Degradation." International Journal for Numerical and Analytical Methods in Geomechanics 27.9 (2003): 705-732. [6] J.D. Rimstidt and H.L. Barnes. "The Kinetics of Silica-water Reactions." Geochimica et Cosmochimica Acta 44.11 (1980): 1683-1699. [7] P.V. Lade, J.A. Yamamuro and P.A. Bopp "Significance of Particle Crushing in Granular Materials." Journal of Geotechnical Engineering, 122.4 (1996): 309-316.

  11. Effects of Mo sources on Mo doped SrTiO{sub 3} powder prepared by spray pyrolysis for H{sub 2} evolution under visible light irradiation

    Energy Technology Data Exchange (ETDEWEB)

    Kang, Hyun Woo, E-mail: hyunwookang@kaeri.re.kr [Korea Atomic Energy Research Institute, Daedeok-daero 989-111, Yuseong-gu, Daejeon 305-353 (Korea, Republic of); Park, Seung Bin [Department of Chemical and Biomolecular Engineering, Korea Advanced Institute of Science and Technology, Daehak-ro 291, Yuseong-gu, Daejeon 305-701 (Korea, Republic of)

    2016-09-15

    Highlights: • Three types of molybdenum ions (Mo{sup 6+}, Mo{sup 4+}, and Mo{sup 2+}) were doped into SrTiO{sub 3}. • Molybdenum oxidation states were changed by photocatalyst preparation process. • Hydrogen was evolved by molybdenum doped SrTiO{sub 3} under visible light. • SrTiO{sub 3} doped with Mo{sup 4+} and Mo{sup 6+} showed the best photocatalytic activity. - Abstract: SrTiO{sub 3} was doped with three types of molybdenum ions (Mo{sup 6+}, Mo{sup 4+}, and Mo{sup 2+}) by spray pyrolysis. The molybdenum ions narrowed the band gap of SrTiO{sub 3} to allow hydrogen evolution under visible-light irradiation. The molybdenum-doped SrTiO{sub 3} photocatalyst prepared from MoO{sub 2} (0.4 mol%) exhibited hydrogen evolution up to a rate of 1410.3 μmol g{sup −1} h{sup −1} with an induction period of 1 h. The use of MoO{sub 2} resulted in SrTiO{sub 3} doping by Mo{sup 6+} and Mo{sup 4+} ions, which enhanced the hydrogen evolution by forming 4d-like states under the conduction band. The ionic structure of SrTiO{sub 3} doped with Mo{sup 4+} and Mo{sup 6+} could be expressed as Sr[Ti{sup 4+}{sub 1−x−y}(Mo{sup 4+}{sub x}Mo{sup 6+}{sub y})]O{sub 3} from the X-ray photoelectron spectra.

  12. Structural and electronic properties of germanene/MoS2 monolayer and silicene/MoS2 monolayer superlattices

    Science.gov (United States)

    Li, Xiaodan; Wu, Shunqing; Zhou, Sen; Zhu, Zizhong

    2014-03-01

    Superlattice provides a new approach to enrich the class of materials with novel properties. Here, we report the structural and electronic properties of superlattices made with alternate stacking of two-dimensional hexagonal germanene (or silicene) and a MoS2 monolayer using the first principles approach. The results are compared with those of graphene/MoS2 superlattice. The distortions of the geometry of germanene, silicene, and MoS2 layers due to the formation of the superlattices are all relatively small, resulting from the relatively weak interactions between the stacking layers. Our results show that both the germanene/MoS2 and silicene/MoS2 superlattices are manifestly metallic, with the linear bands around the Dirac points of the pristine germanene and silicene seem to be preserved. However, small band gaps are opened up at the Dirac points for both the superlattices due to the symmetry breaking in the germanene and silicene layers caused by the introduction of the MoS2 sheets. Moreover, charge transfer happened mainly within the germanene (or silicene) and the MoS2 layers (intra-layer transfer), as well as some part of the intermediate regions between the germanene (or silicene) and the MoS2 layers (inter-layer transfer), suggesting more than just the van der Waals interactions between the stacking sheets in the superlattices.

  13. High performance Mo adsorbent PZC

    Energy Technology Data Exchange (ETDEWEB)

    Anon.

    1998-10-01

    We have developed Mo adsorbents for natural Mo(n, {gamma}){sup 99}Mo-{sup 99m}Tc generator. Among them, we called the highest performance adsorbent PZC that could adsorb about 250 mg-Mo/g. In this report, we will show the structure, adsorption mechanism of Mo, and the other useful properties of PZC when you carry out the examination of Mo adsorption and elution of {sup 99m}Tc. (author)

  14. Interface Structure, Band Alignment, and Built-In Potentials at LaFeO3<mo>/mo>n-SrTiO3 Heterojunctions

    Energy Technology Data Exchange (ETDEWEB)

    Comes, Ryan; Chambers, Scott

    2016-11-22

    We demonstrate that LaFeO3/n-SrTiO3(001) heterojunctions engineered to have opposite interface polarities exhibit very similar band offsets and built-in potentials within the LaFeO3 layer of the same sign. However, heterojunctions with the TiO20-LaO+ interface structure attract electronic charge from the n-STO substrate, whereas those with the SrO0-FeO2-1 interface structure do not. These results suggest that the latter would more effectively facilitate photogenerated electron-hole pair separation than the former, an important result for photoelectrochemical water splitting

  15. Plasmons on the edge of MoS2 nanostructures

    DEFF Research Database (Denmark)

    Andersen, Kirsten; Jacobsen, Karsten Wedel; Thygesen, Kristian Sommer

    2014-01-01

    Using ab initio calculations we predict the existence of one-dimensional (1D), atomically confined plasmons at the edges of a zigzag MoS2 nanoribbon. The strongest plasmon originates from a metallic edge state localized on the sulfur dimers decorating the Mo edge of the ribbon. A detailed analysis...... of the dielectric function reveals that the observed deviations from the ideal 1D plasmon behavior result from single-particle transitions between the metallic edge state and the valence and conduction bands of the MoS2 sheet. The Mo and S edges of the ribbon are clearly distinguishable in calculated spatially...... resolved electron energy loss spectrum owing to the different plasmonic properties of the two edges. The edge plasmons could potentially be utilized for tuning the photocatalytic activity of MoS2 nanoparticles....

  16. Electronic structure of β-RbNd(MoO4)2 by XPS and XES

    Science.gov (United States)

    Atuchin, V. V.; Khyzhun, O. Y.; Chimitova, O. D.; Molokeev, M. S.; Gavrilova, T. A.; Bazarov, B. G.; Bazarova, J. G.

    2015-02-01

    β-RbNd(MoO4)2 microplates have been prepared by the multistage solid state synthesis method. The phase composition and micromorphology of the final product have been evaluated by XRD and SEM methods. The electronic structure of β-RbNd(MoO4)2 molybdate has been studied employing the X-ray photoelectron spectroscopy (XPS) and X-ray emission spectroscopy (XES). For the molybdate, the XPS core-level and valence-band spectra, as well as XES bands representing energy distribution of the Mo 4d- and O 2p-like states, have been measured. It has been established that the O 2p-like states contribute mainly to the upper portion of the valence band with also significant contributions throughout the whole valence-band region. The Mo 4D-like states contribute mainly to a lower valence band portion.

  17. MoS₂ decoration by Mo-atoms and the MoS₂-Mo-graphene heterostructure: a theoretical study.

    Science.gov (United States)

    Kvashnin, D G; Sorokin, P B; Seifert, G; Chernozatonskii, L A

    2015-11-21

    Here we propose a completely new covalent heterostructure based on graphene and self-decorated MoS2 monolayers. Detailed investigation of the decoration process of the MoS2 surface by Mo adatoms was performed using first principles DFT methods. Comparison between valence-only and semicore pseudopotentials was performed to correctly describe the interaction between Mo adatoms and the MoS2 surface. It was found that self-decoration by Mo atoms is favorable from an energetic point of view. We studied in detail various decoration paths of Mo atoms on the MoS2 surface. The strong variation of electronic properties after the decoration of MoS2 was found. The impact of the presence of Mo adatoms on the electronic properties of the graphene/MoS2 heterostructure was shown.

  18. Band Together!

    Science.gov (United States)

    Olson, Cathy Applefeld

    2011-01-01

    After nearly a decade as band director at St. James High School in St. James, Missouri, Derek Limback knows that the key to building a successful program is putting the program itself above everything else. Limback strives to augment not only his students' musical prowess, but also their leadership skills. Key to his philosophy is instilling a…

  19. Theoretical study on electronic properties of MoS{sub 2} antidot lattices

    Energy Technology Data Exchange (ETDEWEB)

    Shao, Li; Chen, Guangde; Ye, Honggang, E-mail: hgye@mail.xjtu.edu.cn; Wu, Yelong; Niu, Haibo; Zhu, Youzhang [Department of Applied Physics and the MOE Key Laboratory for Nonequilibrium Synthesis and Modulation of Condensed Matter, Xi' an Jiaotong University, Xi' an, Shaanxi 710049 (China)

    2014-09-21

    Motivated by the state of the art method for etching hexagonal array holes in molybdenum disulfide (MoS{sub 2}), the electronic properties of MoS{sub 2} antidot lattices (MoS{sub 2}ALs) with zigzag edge were studied with first-principles calculations. Monolayer MoS{sub 2}ALs are semiconducting and the band gaps converge to constant values as the supercell area increases, which can be attributed to the edge effect. Multilayer MoS{sub 2}ALs and chemical adsorbed MoS{sub 2}ALs by F atoms show metallic behavior, while the structure adsorbed with H atoms remains to be semiconducting with a tiny bandgap. Our results show that forming periodically repeating structures in MoS{sub 2} can develop a promising technique for engineering nano materials and offer new opportunities for designing MoS{sub 2}-based nanoscale electronic devices and chemical sensors.

  20. Stability Limits of the Liquid Phase in the Layered Mo/Pb/Mo, Mo/Bi/Mo and Mo/In/Mo Film Systems

    Directory of Open Access Journals (Sweden)

    S.I. Petrushenko

    2016-12-01

    Full Text Available The results of the study of supercooling of the fusible metals films between the continuous layers of molybdenum during the crystallization are given. Due to an original in situ technique based on the changes of resistance of samples during heating and cooling directly in the vacuum chamber the values of supercooling in Mo/Pb/Mo, Mo/Bi/Mo, Mo/In/Mo films are determined and the influence of the morphological structure of the bismuth inclusions on the temperature and nature of its supercooled melt crystallization has been found. The substrate temperature change during the condensation of samples, accompanied by a corresponding change in their microstructure, allows realizing both avalanche and diffuse crystallization and changing of supercooling value in the range of 60 to 180 K in Mo/Bi/Mo films.

  1. MoEDAL expands

    CERN Multimedia

    Anaïs Schaeffer

    2011-01-01

    The MoEDAL collaboration deployed a test array of 18 plastic Nuclear Track Etch Detector (NTD) stacks – covering an area of 1 m2 – in the MoEDAL/VELO cavern at Point 8 of the LHC ring in November 2009. This small array was supplemented by a further 110 stacks this past January. The MoEDAL test array, which now covers an area of 8 m2, will reveal its secrets early in 2013. The full MoEDAL detector will be installed in the next long shutdown of the LHC in 2013.   View of the MoEDAL detectors installed at Point 8 of the LHC ring in January 2011. MoEDAL (Monopole and Exotics Detector At the LHC), the seventh LHC experiment, was approved by the CERN Research Board at the end of 2009. Its goal is to search for very specific exotics such as highly ionising massive stable (or pseudo-stable) particles with conventional electrical charge and magnetic monopoles. “The main LHC experiments are designed to detect conventionally charged particles, with conventional ionisation patte...

  2. Synthesis and characterization of MoS2 nanosheets.

    Science.gov (United States)

    Deokar, G; Vignaud, D; Arenal, R; Louette, P; Colomer, J-F

    2016-02-19

    Here, we report on the synthesis of MoS2 nanosheets using a simple two-step additive-free growth technique. The as-synthesized nanosheets were characterized to determine their structure and composition, as well as their optical properties. The MoS2 nanosheets were analyzed by scanning electron microscopy, transmission electron microscopy (TEM), including high-resolution scanning TEM imaging and energy-dispersive x-ray spectroscopy, x-ray photoelectron spectroscopy (XPS), Raman spectroscopy and photoluminescence (PL). The as-produced MoS2 nanosheets are vertically aligned with curved edges and are densely populated. The TEM measurements confirmed that the nanosheets have the 2H-MoS2 crystal structure in agreement with the Raman results. The XPS results revealed the presence of high purity MoS2. Moreover, a prominent PL similar to mechanically exfoliated few and mono-layer MoS2 was observed for the as-grown nanosheets. For the thin (≤50 nm) nanosheets, the PL feature was observed at the same energy as that for a direct band-gap monolayer MoS2 (1.83 eV). Thus, the as-produced high-quality, large-area, MoS2 nanosheets could be potentially useful for various optoelectronic and catalysis applications.

  3. Study of neutron-rich Mo isotopes by the projected shell model approach

    Indian Academy of Sciences (India)

    Gopal Krishan; Rawan Kumar; Rani Devi; S K Khosa

    2014-09-01

    The projected shell model (PSM) calculations have been performed for the neutron-rich even–even 102−110Mo and odd–even 103−109Mo isotopes. The present calculation reproduces the available experimental data on the yrast bands. In case of even–even nuclei, the structure of yrast bands is analysed and electromagnetic quantities are compared with the available experimental data. The -factors have been predicted for high spin states. For the odd-neutron nuclei, the structures of yrast positive- and negative-parity bands are analysed and found to be in reasonable agreement with the experiments for 103−107Mo. The disagreement of the calculated and observed plots for energy staggering quantity clearly establishes the occurrence of sizable triaxiality in 103,105Mo and also predicts a decrease in the quantum of triaxiality with increasing neutron number and angular momentum for odd mass neutron-rich Mo isotopes.

  4. Strain induced piezoelectric effect in black phosphorus and MoS2 van der Waals heterostructure.

    Science.gov (United States)

    Huang, Le; Li, Yan; Wei, Zhongming; Li, Jingbo

    2015-11-10

    The structural, electronic, transport and optical properties of black phosphorus/MoS2 (BP/MoS2) van der Waals (vdw) heterostructure are investigated by using first principles calculations. The band gap of BP/MoS2 bilayer decreases with the applied normal compressive strain and a semiconductor-to-metal transition is observed when the applied strain is more than 0.85 Å. BP/MoS2 bilayer also exhibits modulation of its carrier effective mass and carrier concentration by the applied compressive strain, suggesting that mobility engineering and good piezoelectric effect can be realized in BP/MoS2 heterostructure. Because the type-II band alignment can facilitate the separation of photo-excited electrons and holes, and it can benefit from the great absorption coefficient in ultra-violet region, the BP/MoS2 shows great potential to be a very efficient ultra-violet photodetector.

  5. First-Principles Study of Mo Segregation in MoNi(111: Effects of Chemisorbed Atomic Oxygen

    Directory of Open Access Journals (Sweden)

    Yanlin Yu

    2015-12-01

    Full Text Available Segregation at metal alloy surfaces is an important issue because many electrochemical and catalytic properties are directly correlated to the surface composition. We have performed density functional theory calculations for Mo segregation in MoNi(111 in the presence of chemisorbed atomic oxygen. In particular, the coverage dependence and possible adsorption-induced segregation phenomena are addressed by investigating segregation energies of the Mo atom in MoNi(111. The theoretical calculated results show that the Mo atom prefers to be embedded in the bulk for the clean MoNi(111, while it segregates to the top-most layer when the oxygen coverage is thicker than 1/9 monolayer (ML. Furthermore, we analyze the densities of states for the clean and oxygen-chemisorbed MoNi(111, and see a strong covalent bonding between Mo d-band states and O p-states. The present study provides valuable insight for exploring practical applications of Ni-based alloys as hydrogen evolution electrodes.

  6. Density functional theory investigation of the electronic structure and thermoelectric properties of layered MoS{sub 2}, MoSe{sub 2} and their mixed-layer compound

    Energy Technology Data Exchange (ETDEWEB)

    Lee, Changhoon; Hong, Jisook [Department of Chemistry, Pohang University of Science and Technology, Pohang 790-784 (Korea, Republic of); Lee, Wang Ro [Faculty of Liberal Education, Chonbuk National University, Jeonju, Jeonbuk 561-756 (Korea, Republic of); Kim, Dae Yeon [Agency for Defense Development (ADD), Chinhae, Kyungnam 645-600 (Korea, Republic of); Shim, Ji Hoon, E-mail: jhshim@postech.ac.kr [Department of Chemistry, Pohang University of Science and Technology, Pohang 790-784 (Korea, Republic of); Divisions of Advanced Nuclear Engineering, Pohang University of Science and Technology, Pohang 790-784 (Korea, Republic of)

    2014-03-15

    First principles density functional theory calculations were carried out for the 2H-MoQ{sub 2} (Q=S and Se) and their hypothetical mixed-layer compound. Due to the different electronegativities of S and Se atoms on MoQ{sub 2}, the band gap size could be adjusted in mixed-layer compound MoS{sub 2}/MoSe{sub 2}. Also, the indirect band gap in pure MoQ{sub 2} compounds is changed to the pseudo direct band gap in mixed-layer MoS{sub 2}/MoSe{sub 2} which is similar to the monolayer compound. The layer mixing enhances the thermoelectric properties because of the increased density of states around the Fermi level and the decreased band gap size. Therefore, we suggest that this layer mixing approach should be regarded as a useful way to modulate their electronic structures and to improve their thermoelectric properties. -- Graphical abstract: On the basis of density functional calculations we predict that the mixed-layer compounds 2H-MoS{sub 2}/2H-MoSe{sub 2}, in which two different layers 2H-MoS{sub 2} and 2H-MoSe{sub 2}, have enhanced thermoelectric properties because of the increased density of states around the Fermi level and the decreased band gap size. Highlights: • We explored a way of improving TE properties of 2H-MoQ{sub 2} on DFT methods. • The mixed-layer compounds MoS{sub 2}/MoSe{sub 2} have enhanced thermoelectric properties. • This is caused by modulated electronic structure of mixed layer compound. • Layer mixing approach should be regarded as a useful way to improve TE properties.

  7. High photocatalytic performance of a type-II α-MoO3@MoS2 heterojunction: from theory to experiment.

    Science.gov (United States)

    Li, Honglin; Yu, Ke; Tang, Zheng; Fu, Hao; Zhu, Ziqiang

    2016-05-18

    For the first time, a systematic study using density functional theory (DFT) has been employed to survey the synergistic effect of α-MoO3@MoS2 with the aim of gaining insights into the role of this heterogeneous structure in a relevant photocatalytic reaction. The geometry, electronic structures and the band edge positions of the α-MoO3@MoS2 composite were computed to explore the characteristics of the heterojunction. This revealed that the established heterogeneous structure could facilitate the separation of the photoinduced carriers into two parts around the interface. The photoinduced electron carriers injected into the conduction band minimum (CBM) of α-MoO3 from the CBM of MoS2 while the hole carriers transferred from the valence band maximum (VBM) of α-MoO3 to the VBM of MoS2. This separation process could markedly restrain the photogenerated electron-hole pair recombination and was further verified by photocurrent and photoluminescence (PL) surveys. Based on the results obtained from computation, we then synthesized the α-MoO3@MoS2 hybrid rod@sphere structure via a facile two-step hydrothermal method. A reasonable formation mechanism of this rod@sphere structured composite was proposed. The enhanced photocatalytic performance originated from the synergistic effect between α-MoO3 and MoS2. On the one hand, the unique structural characteristics of the composite possessed massive MoS2 spheres closely attached to α-MoO3 rods. On the other hand, the staggered type-II band formation also contributed to the effective separation of photoinduced carriers and thus the corresponding photocatalytic activity was far superior to that of the pristine α-MoO3/MoS2 structures. In brief, the general analyses could fully explain the inner mechanism for the improved photocatalytic activity of the composite structure and provide a reference for the research of composite structures in the future.

  8. Work Function Tuning in Two-Dimensional MoS2 Field-Effect-Transistors with Graphene and Titanium Source-Drain Contacts

    Science.gov (United States)

    Baik, Seung Su; Im, Seongil; Choi, Hyoung Joon

    2017-01-01

    Based on the first principles calculation, we investigate the electronic band structures of graphene-MoS2 and Ti-MoS2 heterojunctions under gate-voltages. By simultaneous control of external electric fields and carrier charging concentrations, we show that the graphene’s Dirac point position inside the MoS2 bandgap is easily modulated with respect to the co-varying Fermi level, while keeping the graphene’s linear band structure around the Dirac point. The easy modulation of graphene bands is not confined to the special cases where the conduction-band-minimum point of MoS2 and the Dirac point of graphene are matched up in reciprocal space, but is generalized to their dislocated cases. This flexibility caused by the strong decoupling between graphene and MoS2 bands enhances the gate-controlled switching performance in MoS2-graphene hybrid stacking-device. PMID:28358116

  9. Layer-by-layer thinning of MoSe2 by soft and reactive plasma etching

    Science.gov (United States)

    Sha, Yunfei; Xiao, Shaoqing; Zhang, Xiumei; Qin, Fang; Gu, Xiaofeng

    2017-07-01

    Two-dimensional (2D) transition metal dichalcogenides (TMDs) like molybdenum diselenide (MoSe2) have recently gained considerable interest since their properties are complementary to those of graphene. Unlike gapless graphene, the band structure of MoSe2 can be changed from the indirect band gap to the direct band gap when MoSe2 changed from bulk material to monolayer. This transition from multilayer to monolayer requires atomic-layer-precision thining of thick MoSe2 layers without damaging the remaining layers. Here, we present atomic-layer-precision thinning of MoSe2 nanaosheets down to monolayer by using SF6 + N2 plasmas, which has been demonstrated to be soft, selective and high-throughput. Optical microscopy, atomic force microscopy, Raman and photoluminescence spectra suggest that equal numbers of MoSe2 layers can be removed uniformly regardless of their initial thickness, without affecting the underlying SiO2 substrate and the remaining MoSe2 layers. By adjusting the etching rates we can achieve complete MoSe2 removal and any disired number of MoSe2 layers including monolayer. This soft plasma etching method is highly reliable and compatible with the semiconductor manufacturing processes, thereby holding great promise for various 2D materials and TMD-based devices.

  10. Level structure of [sup 89]Mo

    Energy Technology Data Exchange (ETDEWEB)

    Garcia-Bermudez, G.; Cardona, M.A.; Ribas, R.V.; Filevich, A.; Achterberg, E.; Szybisz, L. (Laboratorio TANDAR, Departamento de Fisica, Comision Nacional de Energia Atomica, Av. del Libertador 8250, 429 Buenos Aires (Argentina))

    1993-10-01

    The level structure of [sup 89]Mo has been studied with the [sup 60]Ni([sup 32]S,2[ital pn]) reaction at 110 MeV beam energy. Mainly two bands of [gamma] rays depopulating states of probable spin-parity values ranging up to (27/2)[sup +] were determined from the excitation function, neutron and [gamma]-[gamma] coincidences, and [gamma]-ray angular distributions. The high-spin states of [sup 89]Mo show a scheme very similar to that of the [sup 87]Zr isotone. The interpretation of these states in terms of the three neutron-hole configuration ([nu][ital g][sub 9/2])[sup [minus]3] and core-excited states is discussed.

  11. Stability and Electronic Properties of Hydrogenated MoS2 Monolayer: A First-Principles Study.

    Science.gov (United States)

    Zhang, Weibin; Zhang, Zhijun; Yang, Woochul

    2015-10-01

    First-principles total energy studies are used to investigate the stability of hydrogenated MoS2 monolayer (MoS2-Hx) (x = 1-8), which is a compound with different numbers of H atoms adsorbed on the MoS2 surface. Energetically, the S-top side of the MoS2 is found to be the most favorable for H-adsorption. H2S and graphene are well-known to be stable, and MoS2-Hx is predicted to be even more stable because its binding energy is lower than that of H2S and its formation energy and adsorption energy are lower than those of graphene. The analysis of the electronic density distribution and the orbital hybrid also shows that MoS2-Hx forms stable structures. In addition, the influence of the number of the adsorbed H-atoms in the MoS2-Hx on the electronic structure of the compound is also investigated. The MoS2-Hx band structure exhibits a dispersion and the MoS2-Hx band gap gradually decreases from 1.72 eV to 0 eV as the number of adsorbed H atoms increases. The corresponding work function increases as a result of the strengthening of the dipole moment formed between the H atoms that are adsorbed and the hydrogenated MoS2.

  12. RoMo

    DEFF Research Database (Denmark)

    Pedersen, Esben Warming; Hornbæk, Kasper

    2011-01-01

    In TUIs, physical/digital conflicts can occur when the digital model does not match the model implied by the spatial lay- out of tangibles. We show how tangible tabletop interfaces (TTI) can be modified to allow robot movement of tangi- bles, thereby avoiding conflicts. We present RoMo, an open...

  13. Plasma nanocoating of thiophene onto MoS2 nanotubes

    Science.gov (United States)

    Türkaslan, Banu Esencan; Dikmen, Sibel; Öksüz, Lütfi; Öksüz, Aysegul Uygun

    2015-12-01

    MoS2 nanotubes were coated with conductive polymer thiophene by atmospheric pressure radio-frequency (RF) glow discharge. MoS2 nanotubes were prepared by thermal decomposition of hexadecylamine (HDA) intercalated laminar MoS2 precursor on anodized aluminum oxide template and the thiophene was polymerized directly on surface of these nanotubes as in situ by plasma method. The effect of plasma power on PTh/MoS2 nanocomposite properties has been investigated by means of Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM and EDX), and X-ray diffraction spectroscopy (XRD). The presence of PTh bands in the FTIR spectra of PTh/MoS2 nanotube nanocomposites corresponding XRD results indicates that the polythiophene coating onto MoS2 nanotube. The chemical structure of PTh is not changed when the plasma power of discharge differ from 117 to 360 W. SEM images of nanocomposites show that when the discharge power is increased between 117 and 360 W the average diameter of PTh/MoS2 nanotube nanocomposites are changed and the structure become more uniformly.

  14. Amniotic constriction bands

    Science.gov (United States)

    ... of function of an arm or a leg. Congenital bands affecting the hand often cause the most problems. Alternative Names Pseudo-ainhum; Streeter dysplasia; Amniotic band sequence; Amniotic constriction bands; Constriction band ...

  15. Electronic and elastic properties of MoS{sub 2}

    Energy Technology Data Exchange (ETDEWEB)

    Li Wei, E-mail: tolwwt@163.co [Laboratory of Quantum Information Technology, School of Physics and Telecommunication Engineering, South China Normal University, 510006, Guangzhou (China); Chen Junfang; He Qinyu [Laboratory of Quantum Information Technology, School of Physics and Telecommunication Engineering, South China Normal University, 510006, Guangzhou (China); Wang Teng [School of Computer, South China Normal University, 510631, Guangzhou (China)

    2010-05-15

    The electronic structures and elastic properties of molybdenum disulfide are studied using first-principles calculations. The energy band structure and density of state (DOS) of MoS{sub 2} at 0 GPa are calculated. The band gap energy of MoS{sub 2} versus the pressure 0-40 GPa is obtained. We find that the band gap energy decreases as the pressure increases. The geometry optimized structural parameters for lithium nitride under different pressures are listed. The parameters a, c, and E (the enthalpy) all decrease with increasing pressure. However, parameter B (the bulk modulus), S (the shear modulus) and Y (the Young's modulus) increase with pressure. The normalized lattice constants and the elastic modulus as two functions of pressure from 0-40 GPa are obtained. All the calculated elastic constants C{sub ij} increase by different rates with increasing pressure.

  16. Photocatalytic Stability of Single- and Few-Layer MoS₂.

    Science.gov (United States)

    Parzinger, Eric; Miller, Bastian; Blaschke, Benno; Garrido, Jose A; Ager, Joel W; Holleitner, Alexander; Wurstbauer, Ursula

    2015-11-24

    MoS2 crystals exhibit excellent catalytic properties and great potential for photocatalytic production of solar fuels such as hydrogen gas. In this regard, the photocatalytic stability of exfoliated single- and few-layer MoS2 immersed in water is investigated by μ-Raman spectroscopy. We find that while the basal plane of MoS2 can be treated as stable under photocatalytic conditions, the edge sites and presumably also defect sites are highly affected by a photoinduced corrosion process. The edge sites of MoS2 monolayers are significantly more resistant to photocatalytic degradation compared to MoS2 multilayer edge sites. The photostability of MoS2 edge sites depends on the photon energy with respect to the band gap in MoS2 and also on the presence of oxygen in the electrolyte. These findings are interpreted in the framework of an oxidation process converting MoS2 into MoOx in the presence of oxygen and photoinduced charge carriers. The high stability of the MoS2 basal plane under photocatalytic treatment under visible light irradiation of extreme light intensities on the order of P ≈ 10 mW/μm(2) substantiates MoS2's potential as photocatalyst for solar hydrogen production.

  17. Theoretical study on strain induced variations in electronic properties of 2H-MoS{sub 2} bilayer sheets

    Energy Technology Data Exchange (ETDEWEB)

    Dong, Liang; Dongare, Avinash M., E-mail: dongare@uconn.edu [Department of Materials Science and Engineering and Institute of Materials Science, University of Connecticut, Storrs, Connecticut 06269 (United States); Namburu, Raju R. [Computational and Information Sciences Directorate, U.S. Army Research Laboratory, Aberdeen Proving Ground, Maryland 21005 (United States); O' Regan, Terrance P.; Dubey, Madan [Sensors and Electron Devices Directorate, U.S. Army Research Laboratory, Adelphi, Maryland 20783 (United States)

    2014-02-03

    The strain dependence of the electronic properties of bilayer sheets of 2H-MoS{sub 2} is studied using ab initio simulations based on density functional theory. An indirect band gap for bilayer MoS{sub 2} is observed for all variations of strain along the basal plane. Several transitions for the indirect band gap are observed for various strains for the bilayer structure. The variation of the band gap and the carrier effective masses for the holes and the electrons for the bilayer MoS{sub 2} structure under conditions of uniaxial strain, biaxial strain, as well as uniaxial stress is investigated.

  18. Tight-Binding and Hueckel Models of Molecular Clusters

    Science.gov (United States)

    1990-05-01

    Chem. Phys. Lett. 163, 323 (1989); Phys. Rev. Lett. 64, 551 (1990). 16. H. Kupka and K. Jug, Chem. Phys. 130, 23 (1989). 17. Y. Wang , T. F. George...D. M. Lindsay and A. C. Beri, J. Chem. Phys. 86, 3493 (1987). 18. D. M. Lindsay, Y. Wang and T. F. George, J. Chem. Phys. 86, 3500 (1987). 23 Table 1...Department of Chemistry Northwestern University University of California Evanston, IL 60208 Irvine, CA 92717 Professor Frank DiSalvo Professor Roald Hoffmann

  19. Occupied and unoccupied electronic structure of Na doped MoS{sub 2}(0001)

    Energy Technology Data Exchange (ETDEWEB)

    Komesu, Takashi; Zhang, Xin; Dowben, P. A. [Department of Physics and Astronomy, Theodore Jorgensen Hall, 855 N 16th St., University of Nebraska, Lincoln, Nebraska 68588-0299 (United States); Le, Duy; Rahman, Talat S. [Department of Physics, University of Central Florida, 4000 Central Florida Blvd., Orlando, Florida 32816 (United States); Ma, Quan; Bartels, Ludwig [Department of Chemistry and the Materials Science and Engineering Program, University of California - Riverside, Riverside, California 92521 (United States); Schwier, Eike F.; Iwasawa, Hideaki; Shimada, Kenya [Hiroshima Synchrotron Radiation Center, Hiroshima University, Higashi-Hiroshima 739-0046 (Japan); Kojima, Yohei; Zheng, Mingtian [Graduate School of Science, Hiroshima University, Higashi-Hiroshima 739-8526 (Japan); Taniguchi, Masaki [Hiroshima Synchrotron Radiation Center, Hiroshima University, Higashi-Hiroshima 739-0046 (Japan); Graduate School of Science, Hiroshima University, Higashi-Hiroshima 739-8526 (Japan)

    2014-12-15

    The influence of sodium on the band structure of MoS{sub 2}(0001) and the comparison of the experimental band dispersion with density functional theory show excellent agreement for the occupied states (angle-resolved photoemission) and qualitative agreement for the unoccupied states (inverse photoemission spectroscopy). Na-adsorption leads to charge transfer to the MoS{sub 2} surface causing an effect similar to n-type doping of a semiconductor. The MoS{sub 2} occupied valence band structure shifts rigidly to greater binding with little change in the occupied state dispersion. Likewise, the unoccupied states shift downward, approaching the Fermi level, yet the amount of the shift for the unoccupied states is greater than that of the occupied states, effectively causing a narrowing of the MoS{sub 2} bandgap.

  20. Dual role of monolayer MoS2 in enhanced photocatalytic performance of hybrid MoS2/SnO2 nanocomposite

    Science.gov (United States)

    Ding, Shuang-Shuang; Huang, Wei-Qing; Yang, Yin-Cai; Zhou, Bing-Xin; Hu, Wang-Yu; Long, Meng-Qiu; Peng, P.; Huang, Gui-Fang

    2016-05-01

    The enhanced photocatalytic performance of various MoS2-based nanomaterials has recently been observed, but the role of monolayer MoS2 is still not well elucidated at the electronic level. Herein, focusing on a model system, hybrid MoS2/SnO2 nanocomposite, we first present a theoretical elucidation of the dual role of monolayer MoS2 as a sensitizer and a co-catalyst by performing density functional theory calculations. It is demonstrated that a type-II, staggered, band alignment of ˜0.49 eV exists between monolayer MoS2 and SnO2 with the latter possessing the higher electron affinity, or work function, leading to the robust separation of photoexcited charge carriers between the two constituents. Under irradiation, the electrons are excited from Mo 4d orbitals to SnO2, thus enhancing the reduction activity of latter, indicating that the monolayer MoS2 is an effective sensitizer. Moreover, the Mo atoms, which are catalytically inert in isolated monolayer MoS2, turn into catalytic active sites, making the monolayer MoS2 to be a highly active co-catalyst in the composite. The dual role of monolayer MoS2 is expected to arise in other MoS2-semiconductor nanocomposites. The calculated absorption spectra can be rationalized by available experimental results. These findings provide theoretical evidence supporting the experimental reports and pave the way for developing highly efficient MoS2-based photocatalysts.

  1. Conduction quantization in monolayer MoS2

    Science.gov (United States)

    Li, T. S.

    2016-10-01

    We study the ballistic conduction of a monolayer MoS2 subject to a spatially modulated magnetic field by using the Landauer-Buttiker formalism. The band structure depends sensitively on the field strength, and its change has profound influence on the electron conduction. The conductance is found to demonstrate multi-step behavior due to the discrete number of conduction channels. The sharp peak and rectangular structures of the conductance are stretched out as temperature increases, due to the thermal broadening of the derivative of the Fermi-Dirac distribution function. Finally, quantum behavior in the conductance of MoS2 can be observed at temperatures below 10 K.

  2. Variability of electrical contact properties in multilayer MoS2 thin-film transistors

    Science.gov (United States)

    Kim, Seong Yeoul; Park, Seonyoung; Choi, Woong

    2014-09-01

    We report the variability of electrical properties of Ti contacts in back-gated multilayer MoS2 thin-film transistors based on mechanically exfoliated flakes. By measuring current-voltage characteristics from room temperature to 240 °C, we demonstrate the formation of both ohmic and Schottky contacts at the Ti-MoS2 junctions of MoS2 transistors fabricated using identical electrode materials under the same conditions. While MoS2 transistors with ohmic contacts exhibit a typical signature of band transport, those with Schottky contacts indicate thermally activated transport behavior for the given temperature range. These results provide the experimental evidence of the variability of Ti metal contacts on MoS2, highlighting the importance of understanding the variability of electronic properties of naturally occurring MoS2 for further investigation.

  3. Surface hardness behaviour of Ti–Al–Mo alloys

    Indian Academy of Sciences (India)

    Raja Ram Prasad; Shankar Azad; A K Singh; R K Mandal

    2008-08-01

    The microhardness characteristics of various micro-constituents formed in the Ti–Al–Mo alloys have been investigated. Four alloys having compositions, Ti–40Al–2Mo, Ti–42Al–2Mo, Ti–40Al–6Mo and Ti–42Al–6Mo, have been chosen for this purpose. All of these were heat treated at 1300°C and 1400°C for 1 h and water quenched. All the specimens after above heat treatments have displayed load independent Vickers hardness values (VHN) around 300 g of applied load. The average surface hardness characteristic of the alloys is largely found to be dictated by the phases that are present. The microstructural specific VHN values vary between 600 and 750. The indentation behaviour, however, is governed by the morphologies and length scales of microstructures. The most remarkable finding of the present study pertains to the formation of shear bands around the periphery of the indenter for a finer basket weave microstructure in the Ti–40Al–2Mo. The cluster of finely located slip steps was clearly seen. Such a report is lacking in literature in this class of alloys.

  4. Tuning Coupling Behavior of Stacked Heterostructures Based on MoS2, WS2, and WSe2

    Science.gov (United States)

    Wang, Fang; Wang, Junyong; Guo, Shuang; Zhang, Jinzhong; Hu, Zhigao; Chu, Junhao

    2017-03-01

    The interlayer interaction of vertically stacked heterojunctions is very sensitive to the interlayer spacing, which will affect the coupling between the monolayers and allow band structure modulation. Here, with the aid of density functional theory (DFT) calculations, an interesting phenomenon is found that MoS2-WS2, MoS2-WSe2, and WS2-WSe2 heterostructures turn into direct-gap semiconductors from indirect-gap semiconductors with increasing the interlayer space. Moreover, the electronic structure changing process with interlayer spacing of MoS2-WS2, MoS2-WSe2, and WS2-WSe2 is different from each other. With the help of variable-temperature spectral experiment, different electronic transition properties of MoS2-WS2, MoS2-WSe2, and WS2-WSe2 have been demonstrated. The transition transformation from indirect to direct can be only observed in the MoS2-WS2 heterostructure, as the valence band maximum (VBM) at the Γ point in the MoS2-WSe2 and WS2-WSe2 heterostructure is less sensitive to the interlayer spacing than those from the MoS2-WS2 heterostructure. The present work highlights the significance of the temperature tuning in interlayer coupling and advance the research of MoS2-WS2, MoS2-WSe2, and WS2-WSe2 based device applications.

  5. Modulation of electronic structures of MoSe2/WSe2 van der Waals heterostructure by external electric field

    Science.gov (United States)

    Zhang, Fang; Li, Wei; Dai, Xianqi

    2017-10-01

    By using first-principles calculations, we investigate the electronic structures of MoSe2/WSe2 van der Waals(vdW) heterostructure by applying external electric field(Eext) perpendicular to the layers. It is demonstrated that MoSe2/WSe2 heterostructure is a type-II vdW heterostructure. The band gap of MoSe2/WSe2 is significantly modulated by Eext, eventually a semiconductor-to-metal transition can be realized. The positive and negative Eext have different effects on the band gap due to the intrinsic spontaneous electric polarization in MoSe2/WSe2 heterostructure. Moreover, MoSe2/WSe2 heterobilayer experiences transitions from type-II to type-I and then to type-II under various Eext. The present study provides great application potential of ultrathin MoSe2/WSe2 heterostructure in future nano- and optoelectronics.

  6. HYBASE : HYperspectral BAnd SElection

    NARCIS (Netherlands)

    Schwering, P.B.W.; Bekman, H.H.P.T.; Seijen, H.H. van

    2009-01-01

    Band selection is essential in the design of multispectral sensor systems. This paper describes the TNO hyperspectral band selection tool HYBASE. It calculates the optimum band positions given the number of bands and the width of the spectral bands. HYBASE is used to assess the minimum number of spe

  7. Probing the Spin-Polarized Electronic Band Structure in Monolayer Transition Metal Dichalcogenides by Optical Spectroscopy

    Science.gov (United States)

    Wang, Zefang; Zhao, Liang; Mak, Kin Fai; Shan, Jie

    2017-02-01

    We study the electronic band structure in the K/K' valleys of the Brillouin zone of monolayer WSe2 and MoSe2 by optical reflection and photoluminescence spectroscopy on dual-gated field-effect devices. Our experiment reveals the distinct spin polarization in the conduction bands of these compounds by a systematic study of the doping dependence of the A and B excitonic resonances. Electrons in the highest-energy valence band and the lowest-energy conduction band have antiparallel spins in monolayer WSe2, and parallel spins in monolayer MoSe2. The spin splitting is determined to be hundreds of meV for the valence bands and tens of meV for the conduction bands, which are in good agreement with first principles calculations. These values also suggest that both n- and p-type WSe2 and MoSe2 can be relevant for spin- and valley-based applications

  8. Wasp-waisted magnetism in hydrothermally grown MoS2 nanoflakes

    Science.gov (United States)

    Chacko, Levna; Swetha, A. K.; Anjana, R.; Jayaraj, M. K.; Aneesh, P. M.

    2016-11-01

    Two-dimensional semiconducting materials are emanating as a requisite group of materials for future nanoscale electronics and optoelectronics. Particularly, transition-metal dichalcogenides like molybdenum disulphide (MoS2), a semiconducting inorganic counterpart of graphene have intrigued intensive interest as two-dimensional materials due to its novel functionalities. In this work, the utilization of high pressure and low temperature hydrothermal method offers a facile, versatile synthetic tool for MoS2 nanoflakes formation without the addition of any surfactants. Our experimental results resolve the formation of hexagonal phase, well-ordered stacking of S-Mo-S layers, quantum confinement and interlayer interaction. The strong spin-orbit coupling in MoS2 provides enthralling optical and magnetic properties. A large optical absorption in 400-700 nm region and strong luminescence provide evidence for the indirect to direct band gap transition in MoS2. Magnetic measurement results reveal ferromagnetism for all the MoS2 nanoflakes and also indicate an increase in saturation magnetization with increase in duration of growth. In addition, a wasp-waisted hysteresis loop was also observed for the first time in MoS2 nanostructures indicating multimodal population, increased grain growth and MoS2-MoO3 coupling. Our findings provide important insights into the future applications of MoS2 in high-performance nanodevices and spintronics.

  9. ELECTRONIC STRUCTURE OF BISMUTH MOLYBDENUM OXIDE SINGLE CRYSTAL Bi0.19MoO3

    Institute of Scientific and Technical Information of China (English)

    XIONG RUI; SHI JING; TANG WU-FENG; TIAN DE-CHENG

    2001-01-01

    Single crystal Bi0. 19MoO3 has been grown by fused salt electrolytic technique. X-ray powder diffraction shows that the unit cell parameters are: a=1.9985nm, b=0.4085nm and c=1.4437nm. The temperature dependence of resistivity demonstrates a semiconductor characteristic. X-ray photoemission spectroscopy studies provide that the valence band of Bi0.19MoO3 are made up of oxygen pπ and the r*, r and σ bonding bands formed by orbital combination. The shoulder at 0.4 eV near the top of valence band may be formed from the non-bonding dxy orbitals of some Mo atoms. The O1s core-electron spectrum reveals the presence of two inequivalent bonds of oxygen ions in Bi0.19MoO3. Bi4f core-level spectrum shows two bonding characters of Bi atoms in bismuth molybdenum oxide single crystals. Mo3d core-level spectrum could be decomposed into two kinds of valence states of molybdenum(Mo+5 and Mo+6).

  10. Structural evolution in crystalline MoO{sub 3} nanoparticles with tunable size

    Energy Technology Data Exchange (ETDEWEB)

    Barros Santos, Elias de; Aparecido Sigoli, Fernando [Functional Materials Laboratory, Institute of Chemistry, University of Campinas, UNICAMP, PO Box 6154, Zip Code 13083-970 Campinas, SP (Brazil); Odone Mazali, Italo, E-mail: mazali@iqm.unicamp.br [Functional Materials Laboratory, Institute of Chemistry, University of Campinas, UNICAMP, PO Box 6154, Zip Code 13083-970 Campinas, SP (Brazil)

    2012-06-15

    In this study MoO{sub 3} nanoparticles were prepared in porous Vycor glass by impregnation-decomposition cycles (IDC) with molybdenum(VI) 2-ethylhexanoate. X-ray diffraction data show that the nanoparticles are crystalline and are in the orthorhombic {alpha}-MoO{sub 3} phase. Raman spectroscopy data also indicate the formation of this phase. The profiles in the Raman spectra changed with the number of IDC, indicating a structural evolution of the MoO{sub 3} nanoparticles. The IDC methodology promoted a linear mass increase and allowed tuning the nanoparticle size. Analysis of HRTEM images revealed that for 3, 5 and 7 IDC, the MoO{sub 3} nanoparticle average diameters are 3.2, 3.6 and 4.2 nm. Diffuse reflectance spectroscopy indicates a consistent red shift in the band gap from 3.35 to 3.29 eV as the size increases from 3.2 to 4.2 nm. This observed red shift in the band gap of the MoO{sub 3} nanoparticles is presumably due to quantum confinement effects. - Graphical abstract: Modification of profile Raman spectra for crystalline MoO{sub 3} nanoparticles in function of the particle size. Highlights: Black-Right-Pointing-Pointer Structural evolution of the MoO{sub 3} nanoparticles as a function of the crystallite size. Black-Right-Pointing-Pointer Tunable optical properties by controlling the MoO{sub 3} nanoparticle size. Black-Right-Pointing-Pointer The impregnation-decomposition methodology allowed tuning the nanoparticle size. Black-Right-Pointing-Pointer The red shift in the band gap of the MoO{sub 3} nanoparticles is due to quantum size effect. Black-Right-Pointing-Pointer The short-distance order in MoO{sub 3} nanoparticle is function to area/volume ratio.

  11. Metastable monoclinic ZnMoO4: hydrothermal synthesis, optical properties and photocatalytic performance.

    Science.gov (United States)

    Lv, Li; Tong, Wenming; Zhang, Yanbing; Su, Yiguo; Wang, Xiaojing

    2011-11-01

    Metastable monoclinic ZnMoO4 was successfully synthesized via a hydrothermal route with variation of reaction temperatures and time at pH value of 5.7. Systematic sample characterizations were carried out, including X-ray powder diffraction, scanning electron microscopy, Fourier transformed infrared spectra, UV-visible diffuse reflectance spectra, and photoluminescence spectra. The results show that all as-prepared ZnMoO4 samples were demonstrated to crystallize in a pure-phase of monoclinic wolframite structure. All samples were formed in plate-like morphology. Six IR active vibrational bands were observed in the wave number range of 400-900 cm(-1). The band gap of as-prepared ZnMoO4 was estimated to be 2.86 eV by Tauc equation. Photoluminescence measurement indicates that as-prepared ZnMoO4 exhibits a broad blue-green emission under excitation wavelength of 280 nm at room temperature. Photocatalytic activity of as-prepared ZnMoO4 was examined by monitoring the degradation of methyl orange dye in an aqueous solution under UV radiation of 365 nm. The as-prepared ZnMoO4 obtained at 180 degrees C for 40 h showed the best photocatalytic activity with completing degradation of MO in irradiation time of 120 min. Consequently, monoclinic ZnMoO4 proved to be an efficient near visible light photocatalyst.

  12. Effect of radio frequency power on composition, structure and optical properties of MoSe{sub x} thin films

    Energy Technology Data Exchange (ETDEWEB)

    Feng, Li-ping, E-mail: lpfeng@nwpu.edu.cn; Li, Ning; Liu, Zhengtang

    2014-07-01

    MoSe{sub x} films were prepared by radio frequency (RF) magnetron sputtering under various RF powers in the range of 40–130 W. Effects of RF power on composition, structure and optical properties of MoSe{sub x} films were investigated. Results show that the chemical bonding, binding energy, structure, and optical properties of MoSe{sub x} films depend greatly on RF power. When the RF power varies from 40 to 70 W, the bonding atomic ratio of Se/Mo in MoSe{sub x} films increase and Mo 3d{sub 5/2} and Se 3d{sub 5/2} peaks shift towards lower binding energies. With further increase in the RF power from 70 to 130 W, the bonding atomic ratio of Se/Mo in MoSe{sub x} films decreases and Mo 3d{sub 5/2} and Se 3d{sub 5/2} peaks move to higher binding energies. Structures of MoSe{sub x} films are amorphous with the RF power ≤70 W, whereas structures of MoSe{sub x} films exhibit nanostructure with the RF power >70 W. Moreover, MoSe{sub x} films deposited at 70 W have larger refractive index, lower extinction coefficient, and higher band gap than those deposited at other RF power.

  13. Novel electronic properties in silicene on MoSe{sub 2} monolayer: An excellent prediction for FET

    Energy Technology Data Exchange (ETDEWEB)

    Li, Sheng-shi; Zhang, Chang-wen, E-mail: zhchwsd@163.com; Ji, Wei-xiao

    2015-08-15

    We perform first-principles calculations to study the energetics and electronic properties of silicene and MoSe{sub 2} heterobilayers (Si@MoSe{sub 2} HBLs). It is found that the silicene is bound to MoSe{sub 2} substrate with a binding energy of −0.56 eV per silicon atom, indicating a weak interaction between two layers. The nearly linear band dispersion character of silicene with a sizable band gap is obtained in Si@MoSe{sub 2}, due to the variation of on-site energy induced by MoSe{sub 2} substrate. Remarkably, the band gaps and electron effective mass (EEM) of HBLs can effectively be tuned by interlayer spacing, external electric field, and strains. These findings indicate that Si@MoSe{sub 2} HBLs are promising candidates for high-performance silicene-based FET channel operating at room temperature, in which both finite band gap and high carrier mobility are obtained. - Highlights: • The nearly linear band dispersion of silicene is remained. • The band gaps can be modulated by spacing distance, strain and electric field. • The electron effective mass also demonstrates an ideal adjustable range. • The high carrier mobility can also be preserved.

  14. Tuning the electronic coupling in Mo2-Mo2 systems by variation of the coordinating atoms of the bridging ligands.

    Science.gov (United States)

    Shu, Yao; Lei, Hao; Tan, Ying Ning; Meng, Miao; Zhang, Xiao Chun; Liu, Chun Y

    2014-10-21

    Three novel [Mo2]-bridge-[Mo2] complexes were synthesized by a convergent assembling reaction of the dimetal precursor Mo2(DAniF)3(O2CCH3) (DAniF = N,N'-di(p-anisyl)formamidinate) with the bridging ligands terephthalamidine, terephthalamide and dithioterephthalamide. The structures of these compounds, [Mo2(DAniF)3]2[μ-1,4-{C(E)NH}2-C6H4] (E = NH (), O () or S ()), were determined, either by X-ray crystallography or (1)H NMR spectroscopy, to be the analogues of the terephthalate bridged dimolybdenum dimer. These compounds are structurally and electronically closely related by having the same structural skeleton and similar bonding parameters, which allowed us to analyze the differences between N, O and S atoms on the bridging ligand in promoting electronic interaction between the two [Mo2] units. In the electronic spectra, the metal to ligand charge transfer absorption bands, attributed to the HOMO (dδ) → LUMO (pπ*) transition, was red shifted as the variable atoms change from N to O to S. The mixed-valence species (+), (+) and (+), generated by one-electron oxidation of the neutral precursors and measured in situ, exhibited characteristic intervalence absorption bands, for which the energy and half-height bandwidth decreased from (+) to (+). Therefore, in comparison to O atoms, S atoms are capable of enhancing the electronic coupling between the two [Mo2] units, and the incorporation of N atoms to the bridging ligands slightly diminished the metal-metal interaction. The molecular structures and spectroscopic properties of these compounds were simulated by theoretical calculations at DFT level on the simplified models, which gave results consistent with the experimental observations.

  15. Interface properties of CVD grown graphene transferred onto MoS2(0001).

    Science.gov (United States)

    Coy Diaz, Horacio; Addou, Rafik; Batzill, Matthias

    2014-01-21

    Heterostructures of dissimilar 2D materials are potential building blocks for novel materials and may enable the formation of new (photo)electronic device architectures. Previous work mainly focused on supporting graphene on insulating wide-band gap materials, such as hex-BN and mica. Here we investigate the interface between zero-band gap semiconductor graphene and band-gap semiconductor MoS2 as a potential building block for entirely 2D-material based semiconducting devices. We show that solution transfer results in water trapping at the interface which may be removed by annealing to ~300 °C in a vacuum. After removal of the water, by high temperature annealing, ultraflat graphene is obtained on MoS2 with only a very weak moiré pattern observable in scanning tunneling microscopy images due to lattice mismatch and random alignment of graphene with respect to the MoS2 substrate. Photoemission spectroscopy indicates interface dipole formation, p-type doping of graphene by ~0.09 eV downward shift of the Fermi-level below the Dirac point, and a negative space charge region in bulk MoS2. Interestingly, valence band spectra of the graphene covered MoS2 surface indicate a band gap narrowing of the MoS2 surface by ~0.1 eV. This band gap reduction at the surface is further evidence that interlayer van der Waals interactions critically influence the band structure of 2D-layered dichalcogenides and suggest that interfacing with dissimilar van der Waals materials allows tuning of their electronic properties.

  16. First principles calculations of the interface properties of a-Al2O3/MoS2 and effects of biaxial strain

    Science.gov (United States)

    Shi, Li-Bin; Li, Ming-Biao; Xiu, Xiao-Ming; Liu, Xu-Yang; Zhang, Kai-Cheng; Liu, Yu-Hui; Li, Chun-Ran; Dong, Hai-Kuan

    2017-05-01

    An amorphous Al2O3 (a-Al2O3)/MoS2 interface has attracted much attention because of its unique properties. In this study, the interface behaviors under non-strain and biaxial strain are investigated by first principles calculations based on the density functional theory. First of all, the generation process of the a-Al2O3 sample is described by molecular dynamics. The calculated bandgap of a-Al2O3 is 3.66 eV for generalized gradient approximation-Perdew, Burke, and Ernzerhof and 5.26 eV for Heyd-Scuseria-Ernzerhof functional. Then, we give a detailed description of the band alignment for the a-Al2O3/MoS2 interface. The valence band offset and conduction band offset change with the number of MoS2 layers. It is noted that the valence band maximum (VBM) of MoS2 moves upward as the number of MoS2 layers is increased. The leakage current for metal/a-Al2O3/MoS2 MOS is also illustrated. At last, the band structure of monolayer MoS2 under biaxial strain ranging from -6% to 6% is discussed, and the impact of the biaxial strain on the band offset is investigated. The VBM of monolayer MoS2 moves downward as the strain changes from compressive to tensile.

  17. Photoemission study on the formation of Mo contacts to CuInSe2

    Science.gov (United States)

    Nelson, A. J.; Niles, D. W.; Kazmerski, L. L.; Rioux, D.; Patel, R.; Hoechst, H.

    1992-08-01

    Synchrotron radiation soft-X-ray photoemission spectroscopy was used to investigate the development of the electronic structure at the Mo/CuInSe2 interface. Mo overlayers were e-beam deposited in steps on single-crystal n-type CuInSe2 at ambient temperature. Photoemission measurements were acquired after each growth in order to observe changes in the valence-band electronic structure as well as changes in the In 4d, Se 3d, and Mo 4d core lines. Photoemission measurements on the valence-band and core lines were also obtained after annealing. The results were used to correlate the interface chemistry with the electronic structure at this interface and to directly determine the maximum possible Schottky barrier height to be not greater than 0.2 eV at the Mo/CuInSe2 junction before annealing, thus showing that this contact is essentially ohmic.

  18. Near-infrared photocatalytic activity induced by intrinsic defects in Bi2MO6 (M = W, Mo).

    Science.gov (United States)

    Jing, Tao; Dai, Ying; Wei, Wei; Ma, Xiangchao; Huang, Baibiao

    2014-09-14

    The electronic structure and related photocatalytic properties of Bi2MO6 (M = W, Mo) with various intrinsic defects are studied based on the first-principles density functional theory (DFT). Our results indicate that O vacancies form easily in both Bi2WO6 and Bi2MoO6 under Bi rich/O poor conditions. The near-infrared light transitions can be realized involving electrons from the O vacancy induced impurity states within the band gap to the conduction band. Rather than acting as photogenerated carrier recombination centers, the impurity states caused by O vacancies favor the transfer of photogenerated holes and further benefit the photocatalytic process due to the delocalized nature. The spatial separation of photogenerated carriers among different layers can be realized, which reduces the carrier recombination and improves the photocatalytic activity. In addition, Bi2WO6 with O vacancies is desirable for having better near-infrared photocatalytic performance than Bi2MoO6 due to the larger mobility of photogenerated holes.

  19. MoO{sub 3} incorporation in magnesium aluminosilicate glasses

    Energy Technology Data Exchange (ETDEWEB)

    Tan, Shengheng; Ojovan, Michael I.; Hyatt, Neil C.; Hand, Russell J.

    2015-03-15

    Molybdate has a very low solubility in silicate and borosilicate glass systems and its excess presence in nuclear waste glass can cause the formation of a readily soluble “yellow phase”. In this study, the incorporation of molybdenum oxide (MoO{sub 3}) in a magnesium aluminosilicate glass system has been investigated. The prepared glasses show a higher than 90% molybdenum retention rate and up to 5.34 mol% (12.28 wt%) MoO{sub 3} can be incorporated into these glasses without causing visible phase separation. The incorporation of MoO{sub 3} increases glass density, decreases glass transition and crystallisation temperatures and intensifies Raman bands assigned to vibrations of MoO{sub 4}{sup 2−} units. When excess molybdate is added liquid–liquid phase separation and crystallisation occurs. The separated phase is spherical, 200–400 nm in diameter and randomly dispersed. Based on powder X-ray diffraction, Raman spectroscopy and transmission electron microscopy, the separated phase is identified as MgMoO{sub 4}.

  20. Carrier plasmon induced nonlinear band gap renormalization in two-dimensional semiconductors.

    Science.gov (United States)

    Liang, Yufeng; Yang, Li

    2015-02-13

    In reduced-dimensional semiconductors, doping-induced carrier plasmons can strongly couple with quasiparticle excitations, leading to a significant band gap renormalization. However, the physical origin of this generic effect remains obscure. We develop a new plasmon-pole theory that efficiently and accurately captures this coupling. Using monolayer MoS(2) and MoSe(2) as prototype two-dimensional (2D) semiconductors, we reveal a striking band gap renormalization above 400 meV and an unusual nonlinear evolution of their band gaps with doping. This prediction significantly differs from the linear behavior that is observed in one-dimensional structures. Notably, our predicted band gap renormalization for MoSe(2) is in excellent agreement with recent experimental results. Our developed approach allows for a quantitative understanding of many-body interactions in general doped 2D semiconductors and paves the way for novel band gap engineering techniques.

  1. Effects of plasma treatment on surface properties of ultrathin layered MoS2

    Science.gov (United States)

    Kim, Suhhyun; Choi, Min Sup; Qu, Deshun; Ra, Chang Ho; Liu, Xiaochi; Kim, Minwoo; Song, Young Jae; Jong Yoo, Won

    2016-09-01

    This work investigates the use of oxygen plasma (O2) treatment, applied as an inductively coupled plasma, to control the thickness and work function of a MoS2 layer. Plasma-etched MoS2 exhibited a surface roughness similar to that of the pristine MoS2. The MoS2 field effect transistors fabricated using the plasma-etched MoS2 displayed a higher n-type doping concentration than that of pristine MoS2. The x-ray photoelectron spectroscopy was performed to analyze chemical composition to demonstrate the minimum level of chemical reactions occurred upon plasma treatment. Moreover, Kelvin probe force microscopy measurements were conducted to probe the changes in the work function that could be attributed to the changes in the surface potential. The measured work functions suggest the modification of a band structure and n-doping effect after plasma treatments that depended on the number of MoS2 layers. This study suggests that the O2 plasma can control the layer number of the MoS2 as well as the electronic properties of a MoS2 film.

  2. The Interface between Gd and Monolayer MoS2: A First-Principles Study

    KAUST Repository

    Zhang, Xuejing

    2014-12-08

    We analyze the electronic structure of interfaces between two-, four- and six-layer Gd(0001) and monolayer MoS2 by first-principles calculations. Strong chemical bonds shift the Fermi energy of MoS2 upwards into the conduction band. At the surface and interface the Gd f states shift to lower energy and new surface/interface Gd d states appear at the Fermi energy, which are strongly hybridized with the Mo 4d states and thus lead to a high spin-polarization (ferromagnetically ordered Mo magnetic moments of 0.15 μB). Gd therefore is an interesting candidate for spin injection into monolayer MoS2.

  3. Hydrothermal synthesis of amorphous MoS2nanofiber bundles via acidification of ammonium heptamolybdate tetrahydrate

    Directory of Open Access Journals (Sweden)

    Tharamani CN

    2007-01-01

    Full Text Available AbstractMoS2nanofiber bundles have been prepared by hydrothermal method using ammonium molybdate with sulfur source in acidic medium and maintained at 180 °C for several hours. The obtained black crystalline products are characterized by powder X-ray diffraction (PXRD, Fourier transform infrared spectrometer (FTIR, X-ray photoelectron spectroscopy (XPS, scanning electron microscopy (SEM and transmission electron microscopy (TEM. The PXRD pattern of the sample can be readily indexed as hexagonal 2H-MoS2. FTIR spectrum of the MoS2shows the band at 480 cm−1corresponds to the γas(Mo-S. SEM/TEM images of the samples exhibit that the MoS2nanofiber exist in bundles of 120–300 nm in diameter and 20–25 μm in length. The effects of temperature, duration and other experimental parameters on the morphology of the products are investigated.

  4. Thermoelectric performance of restacked MoS2 nanosheets thin-film.

    Science.gov (United States)

    Wang, Tongzhou; Liu, Congcong; Xu, Jingkun; Zhu, Zhengyou; Liu, Endou; Hu, Yongjing; Li, Changcun; Jiang, Fengxing

    2016-07-15

    MoS2 has been predicted to be an excellent thermoelectric material due to its large intrinsic band gap and high carrier mobility. In this work, we exfoliated bulk MoS2 by the assistance of lithium intercalation and fabricated the restacked MoS2 thin-film using a simple filtration technique. These MoS2 thin-films with different thickness showed different thermoelectric performance. It was found that with the increase of thickness, carrier concentration, electrical conductivity and Seebeck coefficient all showed an increasing trend. In particular, the maximum Seebeck coefficient was able to reach 93.5 μV K(-1). This high thermopower indicates that MoS2 will have ideal thermoelectric performance in the future through optimizing its structure. The highest figure of merit (ZT = 0.01) is calculated in this experiment.

  5. Structural and Electronic Properties of Germanene on MoS2

    Science.gov (United States)

    Zhang, L.; Bampoulis, P.; Rudenko, A. N.; Yao, Q.; van Houselt, A.; Poelsema, B.; Katsnelson, M. I.; Zandvliet, H. J. W.

    2016-06-01

    To date germanene has only been synthesized on metallic substrates. A metallic substrate is usually detrimental for the two-dimensional Dirac nature of germanene because the important electronic states near the Fermi level of germanene can hybridize with the electronic states of the metallic substrate. Here we report the successful synthesis of germanene on molybdenum disulfide (MoS2), a band gap material. Preexisting defects in the MoS2 surface act as preferential nucleation sites for the germanene islands. The lattice constant of the germanene layer (3.8 ±0.2 Å ) is about 20% larger than the lattice constant of the MoS2 substrate (3.16 Å). Scanning tunneling spectroscopy measurements and density functional theory calculations reveal that there are, besides the linearly dispersing bands at the K points, two parabolic bands that cross the Fermi level at the Γ point.

  6. Electronic Structures of PbMoO4 Crystals with F-Type Colour Centres

    Institute of Scientific and Technical Information of China (English)

    CHEN Jian-Yu; ZHANG Qi-Ren; LIU Ting-Yu; SHAO Ze-Xu; PU Chun-Ying

    2007-01-01

    Electronic structures of PbMo04 crystals containing F-type colour centres with the lattice structure optimized are studied within the framework of the fully relativistic self-consistent Dirac-SIater theory, using a numerically discrete variational (DV-Xα) method. The calculated results show that F and F+ centres have donor energy levels in the forbidden band. The optical transition energies are 2.166eV and 2.197eV, respectively, corresponding to the 580 nm absorption bands in PbMoO4 crystal. The 580 nm absorption band in PbMoO4 is originated from the F-type colour centres.

  7. Structure of nearly degenerate dipole bands in {sup 108}Ag

    Energy Technology Data Exchange (ETDEWEB)

    Sethi, J. [Tata Institute of Fundamental Research, Colaba, Mumbai 400 005 (India); Palit, R., E-mail: palit@tifr.res.in [Tata Institute of Fundamental Research, Colaba, Mumbai 400 005 (India); Saha, S.; Trivedi, T. [Tata Institute of Fundamental Research, Colaba, Mumbai 400 005 (India); Bhat, G.H.; Sheikh, J.A. [Department of Physics, University of Kashmir, Srinagar 190 006 (India); Datta, P. [Ananda Mohan College, Kolkata 700009 (India); Carroll, J.J. [US Army Research Laboratory, Adelphi, MD 20783 (United States); Chattopadhyay, S. [Saha Institute of Nuclear Physics, Kolkata 700064 (India); Donthi, R. [Tata Institute of Fundamental Research, Colaba, Mumbai 400 005 (India); Garg, U. [University of Notre Dame, Notre Dame, IN 46556 (United States); Jadhav, S.; Jain, H.C. [Tata Institute of Fundamental Research, Colaba, Mumbai 400 005 (India); Karamian, S. [Joint Institute for Nuclear Research, Dubna 141980 (Russian Federation); Kumar, S. [University of Delhi, Delhi 110007 (India); Litz, M.S. [US Army Research Laboratory, Adelphi, MD 20783 (United States); Mehta, D. [Panjab University, Chandigarh 160014 (India); Naidu, B.S. [Tata Institute of Fundamental Research, Colaba, Mumbai 400 005 (India); Naik, Z. [Sambalpur University, Sambalpur 143005 (India); Sihotra, S. [Panjab University, Chandigarh 160014 (India); and others

    2013-08-09

    The high spin negative parity states of {sup 108}Ag have been investigated with the {sup 11}B + {sup 100}Mo reaction at 39 MeV beam energy using the INGA facility at TIFR, Mumbai. From the γ–γ coincidence analysis, an excited negative parity band has been established and found to be nearly degenerate with the ground state band. The spin and parity of the levels are assigned using angular correlation and polarization measurements. This pair of degenerate bands in {sup 108}Ag is studied using the recently developed microscopic triaxial projected shell model approach. The observed energy levels and the ratio of the electromagnetic transition probabilities of these bands in this isotope are well reproduced by the present model. Further, it is shown that the partner band has a different quasiparticle structure as compared to the yrast band.

  8. Microstructure and phase transformation behavior of Mo-MoSi2 gradient material

    Institute of Scientific and Technical Information of China (English)

    Ying-Yi Zhang; Yun-Gang Li; Yong-Hong Qi; Xue-Feng Shi

    2015-01-01

    Mo-MoSi2 gradient coating on Mo substrate was prepared by siliconizing process,using the polysilicon as silicon atoms.The gradient layer was analyzed by the experimental results,theoretical analysis,and thermodynamic calculation.The silicon,molybdenum content of gradient coating shows a gradual change regulation.The reaction between silicon and molybdenum is most likely to generate Mo5Si3,then MoSi2,finally Mo3Si,but when the silicon content is excessive,the Mo5Si3 and Mo3Si will react with silicon and generate MoSi2.The gradient layer is mainly constituted by Si and MoSi2,only about 1/10 gradient layer is constituted by Mo5Si3 and Mo3Si,and the stable existences of Mo5Si3 and Mo3Si are mainly determined by the silicon content.Along the Mo substrate to the surface of the coating,the phase compo sition of gradient coating changes as follows:Mo → transition layer,Mo (main phase) + Mo3Si + Mo5Si3 →intermediate layer,and MoSi2 (main phase)+ Mo5Si3 + Si → surface layer MoSi2 (main phase)+ Si,and the experimental temperature has no effect on phase composition of gradient coating.

  9. Remote Plasma Oxidation and Atomic Layer Etching of MoS2.

    Science.gov (United States)

    Zhu, Hui; Qin, Xiaoye; Cheng, Lanxia; Azcatl, Angelica; Kim, Jiyoung; Wallace, Robert M

    2016-07-27

    Exfoliated molybdenum disulfide (MoS2) is shown to chemically oxidize in a layered manner upon exposure to a remote O2 plasma. X-ray photoelectron spectroscopy (XPS), low energy electron diffraction (LEED), and atomic force microscopy (AFM) are employed to characterize the surface chemistry, structure, and topography of the oxidation process and indicate that the oxidation mainly occurs on the topmost layer without altering the chemical composition of underlying layer. The formation of S-O bonds upon short, remote plasma exposure pins the surface Fermi level to the conduction band edge, while the MoOx formation at high temperature modulates the Fermi level toward the valence band through band alignment. A uniform coverage of monolayer amorphous MoO3 is obtained after 5 min or longer remote O2 plasma exposure at 200 °C, and the MoO3 can be completely removed by annealing at 500 °C, leaving a clean ordered MoS2 lattice structure as verified by XPS, LEED, AFM, and scanning tunneling microscopy. This work shows that a remote O2 plasma can be useful for both surface functionalization and a controlled thinning method for MoS2 device fabrication processes.

  10. $\\mathbb{Z}_2$ invariance of Germanene on MoS$_2$ from first principles

    OpenAIRE

    Amlaki, Taher; Bokdam, Menno; Paul J. Kelly

    2016-01-01

    We present a low energy Hamiltonian generalized to describe how the energy bands of germanene ($\\rm \\overline{Ge}$) are modified by interaction with a substrate or a capping layer. The parameters that enter the Hamiltonian are determined from first-principles relativistic calculations for $\\rm \\overline{Ge}|$MoS$_2$ bilayers and MoS$_2|\\rm \\overline{Ge} |$MoS$_2$ trilayers and are used to determine the topological nature of the system. For the lowest energy, buckled germanene structure, the g...

  11. Effect of Mo-doping concentration on the physical behaviour of sprayed ZnO layers

    Science.gov (United States)

    Reddy, T. Sreenivasulu; Reddy, M. Vasudeva; Reddy, K. T. Ramakrishna

    2015-06-01

    Mo-doped zinc oxide layers (MZO) have been prepared on cleaned glass substrates by chemical spray pyrolysis technique by varying Mo-doping concentration in the range, 0 - 5 at. %. The X-ray diffraction studies revealed that all the as prepared layers were polycrystalline in nature and exhibited wurtzite structure. The layers prepared with lower Mo-doping concentration (2 at. %), the films showed the (002) plane as the dominant peak. The optical analysis indicated that all the layers had an average optical transmittance of 80% in the visible region and the evaluated band gap varied in the range, 3.28 - 3.50 eV.

  12. Vacancy formation in MoO3: hybrid density functional theory and photoemission experiments

    KAUST Repository

    Salawu, Omotayo Akande

    2016-09-29

    Molybdenum oxide (MoO3) is an important material that is being considered for numerous technological applications, including catalysis and electrochromism. In the present study, we apply hybrid density functional theory to investigate O and Mo vacancies in the orthorhombic phase. We determine the vacancy formation energies of different defect sites as functions of the electron chemical potential, addressing different charge states. In addition, we investigate the consequences of defects for the material properties. Ultraviolet photoemission spectroscopy is employed to study the valence band of stoichiometric and O defective MoO3. We show that O vacancies result in occupied in-gap states.

  13. Studies on nanosized molybdenum trioxide (α-MoO3) thin films

    Science.gov (United States)

    Khalate, S. A.; Kate, R. S.; Deokate, R. J.

    2017-05-01

    The molybdenum trioxide (α-MoO3) thin films of single orthorhombic phase have been deposited by using spray pyrolysis technique on the glass substrates. α-MoO3 thin films were characterized for structural, morphological and optical measurements. XRD results shows that α-MoO3 thin films are polycrystalline, crystallizes in orthorhombic structure crystalline quality improved with substrate temperature. Surface morphological study shows the conversion of grains into nanorod like structure with increasing substrate temperature. The value of optical band gap shows 2.72 eV at the substrate temperature 400 °C.

  14. Structural instability of the ground state of the U2Mo compound

    OpenAIRE

    Losada, Edith L.; Garcés, Jorge E.

    2015-01-01

    This work reports the structural instability at T=0 K of the U2Mo compound in the structure C11b under the distortion related to the C66 elastic constant. The electronic properties of U2Mo such density of states (DOS), bands and Fermi surface (FS) are studied to understand the source of the instability. The C11b structure can be interpreted as formed by parallel linear chains along the z-directions each one composed by successive U-Mo-U blocks. The hybridization due to electronic interactions...

  15. Mo + C codoped TiO(2) using thermal oxidation for enhancing photocatalytic activity.

    Science.gov (United States)

    Zhang, Jun; Pan, Chunxu; Fang, Pengfei; Wei, Jianhong; Xiong, Rui

    2010-04-01

    The photocatalytic activity of TiO(2) is enhanced mainly through heightening absorption of UV-vis light and improving the separation efficiency of photoinduced electrons and holes. The recent new theoretical research revealed that the TiO(2) codoped with Mo + C is considered to be an optimal doping system. On the basis of this theory, the Mo + C codoped TiO(2) powders were first experimentally synthesized by thermal oxidizing a mixture of TiC and MoO(3) powders in the air. The XRD patterns and the XPS survey spectrum showed that carbon (C) acted as a Ti-O-C band structure and molybdenum (Mo) existed as Mo(6+) in anatase TiO(2). The Mo+C codoped TiO(2) had a 32 nm red shift of the spectrum onset compared with pure anatase TiO(2), and its band gap was reduced from 3.20 to 2.97 eV. The photocurrent of the Mo + C codoped TiO(2) was about 4 times as high as that of pure anatase TiO(2), and its photocatalytic activity on decomposition of methylene blue was enhanced.

  16. Band structure of semiconductors

    CERN Document Server

    Tsidilkovski, I M

    2013-01-01

    Band Structure of Semiconductors provides a review of the theoretical and experimental methods of investigating band structure and an analysis of the results of the developments in this field. The book presents the problems, methods, and applications in the study of band structure. Topics on the computational methods of band structure; band structures of important semiconducting materials; behavior of an electron in a perturbed periodic field; effective masses and g-factors for the most commonly encountered band structures; and the treatment of cyclotron resonance, Shubnikov-de Haas oscillatio

  17. Band alignment of two-dimensional lateral heterostructures

    CERN Document Server

    Zhang, Junfeng; Xie, Weiyu; Zhang, S B

    2016-01-01

    Band alignment in two-dimensional (2D) lateral heterostructures is fundamentally different from three-dimensional (3D), as Schottky barrier height is at the Schottky-Mott limit and band offset is at the Anderson limit, regardless interfacial conditions. This robustness arises because, in the asymptotic limit, effect of interfacial dipole vanishes. First-principles calculations of graphene/h-BN and MoS2/WS2 show that 2D junction width W is typically an order of magnitude longer than 3D. Therefore, heterostructures with dimension less than W can also be made, leading to tunable band alignment.

  18. Tuning the Schottky Barrier at the Graphene/MoS2 Interface by Electron Doping

    DEFF Research Database (Denmark)

    Jin, Chengjun; Rasmussen, Filip Anselm; Thygesen, Kristian Sommer

    2015-01-01

    Using ab initio calculations we investigate the energy level alignment at the graphene/MoS2 heterostructure and the use of electron doping as a strategy to lower the Schottky barrier and achieve a low-resistance Ohmic contact. For the neutral heterostructure, density functional theory (DFT...... layer. In contrast to the case of metal substrates, where the band alignment is governed by Pauli repulsion-induced interface dipoles, the graphene/MoS2 heterostructure shows only a negligible interface dipole. As a consequence, the band alignment at the neutral heterostructure is not changed when...... concentration is shown to be mainly governed by the electrostatic potential resulting from the doping charge....

  19. Band parameters of phosphorene

    DEFF Research Database (Denmark)

    Lew Yan Voon, L. C.; Wang, J.; Zhang, Y.;

    2015-01-01

    Phosphorene is a two-dimensional nanomaterial with a direct band-gap at the Brillouin zone center. In this paper, we present a recently derived effective-mass theory of the band structure in the presence of strain and electric field, based upon group theory. Band parameters for this theory...

  20. Molybdenum(VI) Oxosulfato Complexes in MoO3–K2S2O7–K2SO4 Molten Mixtures: Stoichiometry, Vibrational Properties, and Molecular Structures

    DEFF Research Database (Denmark)

    Kalampounias, Angelos G.; Tsilomelekis, George; Berg, Rolf W.

    2012-01-01

    configuration as a core. The stoichiometry of the dissolution reaction MoO3 + nS2O72– → C2n– was inferred by exploiting the Raman band intensities, and it was found that n = 1. Therefore, depending on the MoO3 content, monomeric MoO2(SO4)22– and/or associated [MoO2(SO4)2]m2m– complexes are formed in the binary...

  1. Low Power Band to Band Tunnel Transistors

    Science.gov (United States)

    2010-12-15

    the E-field and tunneling at the source- pocket junction you form a parasitic NPN + transistor and the injection mechanism of carriers into the...hypothesis that the 1000 ° C, 5s anneal split lead to a very wide pocket and the accidental formation of a NPN + transistor , while the 1000 ° C, 1s anneal...Low Power Band to Band Tunnel Transistors Anupama Bowonder Electrical Engineering and Computer Sciences University of California at Berkeley

  2. Synthesis and Photocatalytic Activity of Mo-Doped TiO2 Nanoparticles

    Directory of Open Access Journals (Sweden)

    Ji-guo Huang

    2015-01-01

    Full Text Available The undoped and Mo-doped TiO2 nanoparticles were synthesized by sol-gel method. The as-prepared samples were characterized by X-ray diffraction (XRD, diffuse reflectance UV-visible absorption spectra (UV-vis DRS, X-ray photoelectron spectra (XPS, and transmission electron microscopy (TEM. The photocatalytic activity was evaluated by photocatalytic degradation of methylene blue under irradiation of a 500 W xenon lamp and natural solar light outdoor. Effects of calcination temperatures and Mo doping amounts on crystal phase, crystallite size, lattice distortion, and optical properties were investigated. The results showed that most of Mo6+ took the place of Ti4+ in the crystal lattice of TiO2, which inhibited the growth of crystallite size, suppressed the transformation from anatase to rutile, and led to lattice distortion of TiO2. Mo doping narrowed the band gap (from 3.05 eV of TiO2 to 2.73 eV of TiMo0.02O and efficiently increased the optical absorption in visible region. Mo doping was shown to be an efficient method for degradation of methylene blue under visible light, especially under solar light. When the calcination temperature was 550°C and the Mo doping amount was 2.0%, the Mo-doped TiO2 sample exhibited the highest photocatalytic activity.

  3. Tunable redox potential of nonmetal doped monolayer MoS2: First principle calculations

    Science.gov (United States)

    Lu, S.; Li, C.; Zhao, Y. F.; Gong, Y. Y.; Niu, L. Y.; Liu, X. J.

    2016-10-01

    Doping is an effective method to alter the electronic behavior of materials by forming new chemical bonds and bringing bond relaxation. With this aid of first principle calculations, the crystal configuration and electronic properties of monolayer MoS2 have been modulated by the nonmetal (NM) dopants (H, B, C, N, O, F, Si, P, Cl, As, Se, Br, Te and I), and the thermodynamic stability depending on the preparation conditions (Mo-rich and S-rich conditions) were discussed. Results shown that, the NM dopants substituted preferentially for S under Mo-rich condition, the electronic distribution around the dopants and the nearby Mo atoms are changed by the new formed Mo-NM bonds and bands relaxation. Compared to pristine monolayer MoS2, the NM ions with odd chemical valences enhance the oxidation potential and reduce the reduction potential of specimens, but the NM ions with even chemical valences have the opposite effects on the redox potentials. Compared to the NM ions with even chemical valences, the lone pair electrons in NM ions with odd chemical valences can extra interact with the Mo ions and reduces the ECBM and EVBM values of specimens. It offers a simple way to design various monolayer MoS2 based catalysts in order to catalyze different materials by chose the reasonable dopants for stronger oxidation or reduction potential.

  4. High-Speed Scalable Silicon-MoS2 P-N Heterojunction Photodetectors

    Science.gov (United States)

    Dhyani, Veerendra; Das, Samaresh

    2017-03-01

    Two-dimensional molybdenum disulfide (MoS2) is a promising material for ultrasensitive photodetector owing to its favourable band gap and high absorption coefficient. However, their commercial applications are limited by the lack of high quality p-n junction and large wafer scale fabrication process. A high speed Si/MoS2 p-n heterojunction photodetector with simple and CMOS compatible approach has been reported here. The large area MoS2 thin film on silicon platform has been synthesized by sulfurization of RF-sputtered MoO3 films. The fabricated molecular layers of MoS2 on silicon offers high responsivity up to 8.75 A/W (at 580 nm and 3 V bias) with ultra-fast response of 10 μsec (rise time). Transient measurements of Si/MoS2 heterojunction under the modulated light reveal that the devices can function up to 50 kHz. The Si/MoS2 heterojunction is found to be sensitive to broadband wavelengths ranging from visible to near-infrared light with maximum detectivity up to ≈1.4 × 1012 Jones (2 V bias). Reproducible low dark current and high responsivity from over 20 devices in the same wafer has been measured. Additionally, the MoS2/Si photodetectors exhibit excellent stability in ambient atmosphere.

  5. Controllable Synthesis of Band Gap-Tunable and Monolayer Transition Metal Dichalcogenide Alloys

    Directory of Open Access Journals (Sweden)

    Sheng-Han eSu

    2014-07-01

    Full Text Available The electronic and optical properties of transition metal dichalcogenide (TMD materials are directly governed by their energy gap; thus, the band gap engineering has become an important topic recently. Theoretical and some experimental results have indicated that these monolayer TMD alloys exhibit direct-gap properties and remain stable at room temperature, making them attractive for optoelectronic applications. Here we systematically compared the two approaches of forming MoS2xSe2(1-x monolayer alloys: selenization of MoS2 and sulfurization of MoSe2. The optical energy gap of as-grown CVD MoS2 can be continuously modulated from 1.86 eV (667 nm to 1.57 eV (790 nm controllable by the reaction temperature. Spectroscopic and microscopic evidences show that the Mo-S bonds can be replaced by the Mo-Se bonds in a random and homogeneous manner. By contrast, the replacement of Mo-Se by Mo-S does not randomly occur in the MoSe2 lattice, where the reaction preferentially occurs along the crystalline orientation of MoSe2 and thus the MoSe2/MoS2 biphases are easily observed in the alloys, which makes the optical band gap of these alloys distinctly different. Therefore, the selenization of metal disulfide is preferred and the proposed synthetic strategy opens up a simple route to control the atomic structure as well as optical properties of monolayer TMD alloys.

  6. 95Mo NMR: hyperfine interactions in MoO3, MoS2, MoSe2 Mo3Se4, MoSi2 and Mo2C.

    Science.gov (United States)

    Bastow, T J

    1998-10-01

    Nuclear hyperfine interactions have been obtained by nuclear magnetic resonance (NMR) for 95Mo in a number of binary Mo compounds, both insulators and metals, which illustrate the interplay between nuclear quadrupole and chemical (Knight) shift terms. The insulating phases are characterised by nuclear spin lattice relaxation times greater than 100 s, demonstrating the ineffectiveness of indirect phonon Raman relaxation for these compounds.

  7. Structure and Electronic Properties of In Situ Synthesized Single-Layer MoS2 on a Gold Surface

    DEFF Research Database (Denmark)

    Sørensen, Signe Grønborg; Füchtbauer, Henrik Gøbel; Tuxen, Anders Kyrme;

    2014-01-01

    When transition metal sulfides such as MoS2 are present in the single-layer form, the electronic properties change in fundamental ways, enabling them to be used, e.g., in two-dimensional semiconductor electronics, optoelectronics, and light harvesting. The change is related to a subtle modification...... of the MoS2 layer resulting in a characteristic moiré pattern. X-ray photoelectron spectroscopy indicates that the system develops the characteristics of n-doped MoS2 due to electron donation. Scanning tunneling spectroscopy furthermore reflects a convolution of MoS2 and Au donor states where the MoS2 band...... structure appears modified at the band gap edges. This electronic effect is further modulated by the moiré periodicity and leads to small substrate-induced electronic perturbations near the conduction band minimum in the band gap of MoS2. The results may be highly relevant in the context of nanopatterned...

  8. Layer-transferred MoS{sub 2}/GaN PN diodes

    Energy Technology Data Exchange (ETDEWEB)

    Lee, Edwin W.; Lee, Choong Hee; Paul, Pran K.; Krishnamoorthy, Sriram; Arehart, Aaron R. [Department of Electrical and Computer Engineering, The Ohio State University, Columbus, Ohio 43210 (United States); Ma, Lu; McCulloch, William D.; Wu, Yiying [Department of Chemistry and Biochemistry, The Ohio State University, Columbus, Ohio 43210 (United States); Rajan, Siddharth [Department of Electrical and Computer Engineering, The Ohio State University, Columbus, Ohio 43210 (United States); Department of Material Science and Engineering, The Ohio State University, Columbus, Ohio 43210 (United States)

    2015-09-07

    Electrical and optical characterization of two-dimensional/three-dimensional (2D/3D) p-molybdenum disulfide/n-gallium nitride (p-MoS{sub 2}/n-GaN) heterojunction diodes are reported. Devices were fabricated on high-quality, large-area p-MoS{sub 2} grown by chemical vapor deposition on sapphire substrates. The processed devices were transferred onto GaN/sapphire substrates, and the transferred films were characterized by X-ray diffraction (XRD) and atomic force microscopy (AFM). On-axis XRD spectra and surface topology obtained from AFM scans were consistent with previously grown high-quality, continuous MoS{sub 2} films. Current-voltage measurements of these diodes exhibited excellent rectification, and capacitance-voltage measurements were used to extract a conduction band offset of 0.23 eV for the transferred MoS{sub 2}/GaN heterojunction. This conduction band offset was confirmed by internal photoemission measurements. The energy band lineup of the MoS{sub 2}/GaN heterojunction is proposed here. This work demonstrates the potential of 2D/3D heterojunctions for novel device applications.

  9. Mo-Si alloy development

    Energy Technology Data Exchange (ETDEWEB)

    Liu, C.T.; Heatherly, L.; Wright, J.L. [Oak Ridge National Lab., TN (United States)

    1996-06-01

    The objective of this task is to develop new-generation corrosion-resistant Mo-Si intermetallic alloys as hot components in advanced fossil energy conversion and combustion systems. The initial effort is devoted to Mo{sub 5}-Si{sub 3}-base (MSB) alloys containing boron additions. Three MSB alloys based on Mo-10.5Si-1.1B (wt %), weighing 1500 g were prepared by hot pressing of elemental and alloy powders at temperatures to 1600{degrees}C in vacuum. Microporosities and glassy-phase (probably silicate phases) formations are identified as the major concerns for preparation of MSB alloys by powder metallurgy. Suggestions are made to alleviate the problems of material processing.

  10. Advances in MoS2-Based Field Effect Transistors (FETs)

    Institute of Scientific and Technical Information of China (English)

    Xin Tong; Eric Ashalley; Feng Lin; Handong Li; Zhiming M. Wang

    2015-01-01

    This paper reviews the original achievements and advances regarding the field effect transistor (FET) fabricated from one of the most studied transition metal dichalcogenides: two-dimensional MoS2. Not like graphene, which is highlighted by a gapless Dirac cone band structure, Monolayer MoS2 is featured with a 1.9 eV gapped direct energy band thus facilitates convenient electronic and/or optoelectronic modulation of its physical properties in FET structure. Indeed, many MoS2 devices based on FET architecture such as phototransistors, memory devices, and sensors have been studied and extraordinary properties such as excellent mobility, ON/OFF ratio, and sensitivity of these devices have been ex-hibited. However, further developments in FET device applications depend a lot on if novel physics would be involved in them. In this review, an overview on advances and developments in the MoS2-based FETs are presented. Engineering of MoS2-based FETs will be discussed in details for understanding contact physics, formation of gate dielectric, and doping strategies. Also reported are demonstrations of device behaviors such as low-frequency noise and photoresponse in MoS2-based FETs, which is crucial for developing electronic and optoelectronic devices.

  11. Electrical transport properties of metal and graphene contacts to MoS2

    Science.gov (United States)

    Luo, Yunqiu (Kelly); Wen, Hua; Zhu, Tiancong

    2014-03-01

    Two-dimensional crystals are an exciting class of materials for novel physics and nanoelectronics. MoS2 and related transition metal dichalcogenides have received tremendous interest due to its native band gap and strong spin orbit coupling. Unlike graphene, the presence of the band gap leads to transistors with high on-off ratios. One important issue is the electrical properties of the contacts to the MoS2. Recent studies have shown the presence of a Schottky barrier and its dependence on the metal workfunction, back gate voltage, and interfacial oxide barriers. In this work, we investigate the interfacial properties of metal to MoS2 contact and graphene to MoS2 contact by studying the junction's Schottky barrier formation and bias dependence. We utilize a polymer based transfer method to precisely position exfoliated graphene flakes onto exfoliated MoS2 flakes. We intensively study various junction combination between monolayer/few-layer graphene and monolayer/few-layer MoS2. Dependence on temperature and back gate will be discussed.

  12. Two-dimensional lateral heterojunction through bandgap engineering of MoS2 via oxygen plasma

    Science.gov (United States)

    Choudhary, Nitin; Islam, Muhammad R.; Kang, Narae; Tetard, Laurene; Jung, Yeonwoong; Khondaker, Saiful I.

    2016-09-01

    The present study explores the structural, optical (photoluminescence (PL)), and electrical properties of lateral heterojunctions fabricated by selective exposure of mechanically exfoliated few layer two-dimensional (2D) molybdenum disulfide (MoS2) flakes under oxygen (O2)-plasma. Raman spectra of the plasma exposed MoS2 flakes show a significant loss in the structural quality due to lattice distortion and creation of oxygen-containing domains in comparison to the pristine part of the same flake. The PL mapping evidences the complete quenching of peak A and B consistent with a change in the exciton states of MoS2 after the plasma treatment, indicating a significant change in its band gap properties. The electrical transport measurements performed across the pristine and the plasma-exposed MoS2 flake exhibit a gate tunable current rectification behavior with a rectification ratio up to 1.3  ×  103 due to the band-offset at the pristine and plasma-exposed MoS2 interface. Our Raman, PL, and electrical transport data confirm the formation of an excellent lateral heterojunction in 2D MoS2 through its bandgap modulation via oxygen plasma.

  13. Electronic structure of the Co ( 0001 )/Mo S2 interface and its possible use for electrical spin injection in a single Mo S2 layer

    Science.gov (United States)

    Garandel, T.; Arras, R.; Marie, X.; Renucci, P.; Calmels, L.

    2017-02-01

    The ability to perform efficient electrical spin injection from ferromagnetic metals into two-dimensional semiconductor crystals based on transition metal dichalcogenide monolayers is a prerequisite for spintronic and valleytronic devices using these materials. Here, the hexagonal close-packed (hcp) Co (0001 ) /Mo S2 interface electronic structure is investigated by first-principles calculations based on the density functional theory. In the lowest energy configuration of the hybrid system after optimization of the atomic coordinates, we show that interface sulfur atoms are covalently bound to one, two, or three cobalt atoms. A decrease of the Co atom spin magnetic moment is observed at the interface, together with a small magnetization of S atoms. Mo atoms also hold small magnetic moments, which can take positive as well as negative values. The charge transfers due to covalent bonding between S and Co atoms at the interface have been calculated for majority and minority spin electrons, and the connections between these interface charge transfers and the induced magnetic properties of the Mo S2 layer are discussed. Band structure and density of states of the hybrid system are calculated for minority and majority spin electrons, taking into account spin-orbit coupling. We demonstrate that Mo S2 bound to the Co contact becomes metallic due to hybridization between Co d and S p orbitals. For this metallic phase of Mo S2 , a spin polarization at the Fermi level of 16% in absolute value is calculated, which could allow spin injection into the semiconducting Mo S2 monolayer channel. Finally, the symmetry of the majority and minority spin electron wave functions at the Fermi level in the Co-bound metallic phase of Mo S2 and the orientation of the border between the metallic and semiconducting phases of Mo S2 are investigated, and their impact on spin injection into the Mo S2 channel is discussed.

  14. Dipole strength distribution below the giant dipole resonance in {sup 92}Mo, {sup 98}Mo and {sup 100}Mo

    Energy Technology Data Exchange (ETDEWEB)

    Rusev, G.Y.

    2006-07-01

    Investigations of the dipole-strength distributions in {sup 92}Mo, {sup 98}Mo and {sup 100}Mo were carried out by means of the method of nuclear resonance fluorescence. The low-lying excitations in the nuclides {sup 92}Mo, {sup 98}Mo and {sup 100}Mo have been studied in photon-scattering experiments at an electron energy of 6 MeV at the ELBE accelerator and at electron energies from 3.2 to 3.8 MeV at the Dynamitron accelerator. Five levels were observed in {sup 92}Mo. Five levels in {sup 98}Mo and 14 in {sup 100}Mo were identified for the first time in the energy range from 2 to 4 MeV. Dipole-strength distributions up to the neutron-separation energies in the nuclides {sup 92}Mo, {sup 98}Mo and {sup 100}Mo have been investigated at the ELBE accelerator. Because of the possible observation of transitions in the neighboring nuclei produced via ({gamma},n) reaction, additional measurements at electron energies of 8.4 and 7.8 MeV, below the neutron-separation energy, were performed on {sup 98}Mo and {sup 100}Mo, respectively. The number of transitions assigned to {sup 92}Mo, {sup 98}Mo and {sup 100}Mo is 340, 485 and 499, respectively, the main part of them being dipole transitions. Statistical properties of the observed transitions are obtained. The continuum contains the ground-state transitions as well as the branching transitions to the low-lying levels and the subsequent deexcitations of these levels. (orig.)

  15. Defect assisted coupling of a MoS2/TiO2 interface and tuning of its electronic structure

    Science.gov (United States)

    Chen, Guifeng; Song, Xiaolin; Guan, Lixiu; Chai, Jianwei; Zhang, Hui; Wang, Shijie; Pan, Jisheng; Tao, Junguang

    2016-09-01

    Although MoS2 based heterostructures have drawn increased attention, the van der Waals forces within MoS2 layers make it difficult for the layers to form strong chemical coupled interfaces with other materials. In this paper, we demonstrate the successful strong chemical attachment of MoS2 on TiO2 nanobelts after appropriate surface modifications. The etch-created dangling bonds on TiO2 surfaces facilitate the formation of a steady chemically bonded MoS2/TiO2 interface. With the aid of high resolution transmission electron microscope measurements, the in-plane structure registry of MoS2/TiO2 is unveiled at the atomic scale, which shows that MoS2[1-10] grows along the direction of TiO2[001] and MoS2[110] parallel to TiO2[100] with every six units of MoS2 superimposed on five units of TiO2. Electronically, type II band alignments are realized for all surface treatments. Moreover, the band offsets are delicately correlated to the surface states, which plays a significant role in their photocatalytic performance.

  16. New quantum spin Hall insulator in two-dimensional MoS2 with periodically distributed pores.

    Science.gov (United States)

    Liu, Peng-Fei; Zhou, Liujiang; Frauenheim, Thomas; Wu, Li-Ming

    2016-03-01

    MoS2, one of the transition metal dichalcogenides (TMDs), has gained a lot of attention due to its excellent semiconductor characteristics and potential applications. Here, based on density functional theory methods, we predict a novel 2D QSH insulator in the porous allotrope of monolayer MoS2 (g-MoS2), consisting of MoS2 squares and hexagons. g-MoS2 has a nontrivial gap as large as 109 meV, comparable with previously reported 1T'-MoS2 (80 meV) and so-MoS2 (25 meV). We demonstrate that the origin of the 2D QSH effect in g-MoS2 originates from the pure d-d band inversion, different from the conventional band inversion between s-p, p-p or d-p orbitals. The new polymorph greatly enriches the TMD family and its stabilities are confirmed using phonon spectrum analysis. In particular, its porous structure endows it with the potential for efficient gas separation and energy storage applications.

  17. Characterization and study of reduction and sulfurization processing in phase transition from molybdenum oxide (MoO{sub 2}) to molybdenum disulfide (MoS{sub 2}) chalcogenide semiconductor nanoparticles prepared by one-stage chemical reduction method

    Energy Technology Data Exchange (ETDEWEB)

    Shomalian, K.; Bagheri-Mohagheghi, M.M.; Ardyanian, M. [Damghan University, School of Physics, Damghan (Iran, Islamic Republic of)

    2017-01-15

    In this research, molybdenum disulfide (MoS{sub 2}) nanoparticles were prepared by chemical reduction method using MoO{sub 3} and thiourea as a precursor. The physical properties of the synthesized MoO{sub 2}-MoS{sub 2} nanoparticles annealed at different temperatures of 200, 300, 750 C have been investigated, before and after exposure to sulfur vapor. The nanostructure of nanoparticles has been characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM), field emission scanning electron microscopy (FE-SEM) analyses and UV-Vis spectrophotometer. The X-ray diffraction analysis showed the formation of MoS{sub 2} single phase at annealing temperature of 750 C in the presence of sulfur vapor. The Raman spectrum of the nanoparticles revealed that the formation of MoS{sub 2} at 750 C after annealing in sulfur vapor. The values of band gap were obtained in the range of 3.64-3.17 eV and 3.47-1.95 eV for MoS{sub 2} nanoparticles before and after exposure to sulfur vapor, respectively. According to SEM images, the grain size decreases with increasing annealing temperature up to 750 C. Also, nanoplate-nanoparticles of MoS{sub 2} are formed at annealing temperature of 200-750 C. The TEM images of MoS{sub 2} nanoparticles at T{sub a} = 750 C confirm that the nanoparticles have a homogeneous distribution with a hexagonal structure. The FTIR spectra of the MoS{sub 2} nanoparticles showed the peaks at about 467 cm {sup -1} belong to the characteristic bands of Mo-S. (orig.)

  18. Characterization and study of reduction and sulfurization processing in phase transition from molybdenum oxide (MoO2) to molybdenum disulfide (MoS2) chalcogenide semiconductor nanoparticles prepared by one-stage chemical reduction method

    Science.gov (United States)

    Shomalian, K.; Bagheri-Mohagheghi, M.-M.; Ardyanian, M.

    2017-01-01

    In this research, molybdenum disulfide (MoS2) nanoparticles were prepared by chemical reduction method using MoO3 and thiourea as a precursor. The physical properties of the synthesized MoO2-MoS2 nanoparticles annealed at different temperatures of 200, 300, 750 °C have been investigated, before and after exposure to sulfur vapor. The nanostructure of nanoparticles has been characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM), field emission scanning electron microscopy (FE-SEM) analyses and UV-Vis spectrophotometer. The X-ray diffraction analysis showed the formation of MoS2 single phase at annealing temperature of 750 °C in the presence of sulfur vapor. The Raman spectrum of the nanoparticles revealed that the formation of MoS2 at 750 °C after annealing in sulfur vapor. The values of band gap were obtained in the range of 3.64-3.17 eV and 3.47-1.95 eV for MoS2 nanoparticles before and after exposure to sulfur vapor, respectively. According to SEM images, the grain size decreases with increasing annealing temperature up to 750 °C. Also, nanoplate-nanoparticles of MoS2 are formed at annealing temperature of 200-750 °C. The TEM images of MoS2 nanoparticles at T a = 750 °C confirm that the nanoparticles have a homogeneous distribution with a hexagonal structure. The FTIR spectra of the MoS2 nanoparticles showed the peaks at about 467 cm-1 belong to the characteristic bands of Mo-S.

  19. Electronic Structure and Luminescence of Quasi-Freestanding MoS2 Nanopatches on Au(111)

    Science.gov (United States)

    2016-01-01

    Monolayers of transition metal dichalcogenides are interesting materials for optoelectronic devices due to their direct electronic band gaps in the visible spectral range. Here, we grow single layers of MoS2 on Au(111) and find that nanometer-sized patches exhibit an electronic structure similar to their freestanding analogue. We ascribe the electronic decoupling from the Au substrate to the incorporation of vacancy islands underneath the intact MoS2 layer. Excitation of the patches by electrons from the tip of a scanning tunneling microscope leads to luminescence of the MoS2 junction and reflects the one-electron band structure of the quasi-freestanding layer. PMID:27459588

  20. Z2 Invariance of Germanene on MoS2 from First Principles

    NARCIS (Netherlands)

    Amlaki, T.; Bokdam, M.; Kelly, P.J.

    2016-01-01

    We present a low energy Hamiltonian generalized to describe how the energy bands of germanene (Ge ¯ ¯ ¯ ¯ ) are modified by interaction with a substrate or a capping layer. The parameters that enter the Hamiltonian are determined from first-principles relativistic calculations for Ge ¯ ¯ ¯ ¯ |MoS

  1. Z2 Invariance of Germanene on MoS2 from First Principles

    Science.gov (United States)

    Amlaki, Taher; Bokdam, Menno; Kelly, Paul J.

    2016-06-01

    We present a low energy Hamiltonian generalized to describe how the energy bands of germanene (Ge ¯ ) are modified by interaction with a substrate or a capping layer. The parameters that enter the Hamiltonian are determined from first-principles relativistic calculations for Ge ¯ |MoS2 bilayers and MoS2|Ge ¯ |MoS2 trilayers and are used to determine the topological nature of the system. For the lowest energy, buckled germanene structure, the gap depends strongly on how germanene is oriented with respect to the MoS2 layer(s). Topologically nontrivial gaps for bilayers and trilayers can be almost as large as for a freestanding germanene layer.

  2. Possible doping strategies for MoS 2 monolayers: An ab initio study

    KAUST Repository

    Dolui, Kapildeb

    2013-08-14

    Density functional theory is used to systematically study the electronic properties of doped MoS2 monolayers, where the dopants are incorporated both via S/Mo substitution or as adsorbates. Among the possible substitutional dopants at the Mo site, Nb is identified as suitable p-type dopant, while Re is the donor with the lowest activation energy. When dopants are simply adsorbed on a monolayer we find that alkali metals shift the Fermi energy into the MoS2 conduction band, making the system n type. Finally, the adsorption of charged molecules is considered, mimicking an ionic liquid environment. We find that molecules adsorption can lead to both n- and p-type conductivity, depending on the charge polarity of the adsorbed species. © 2013 American Physical Society.

  3. Effect of rhenium doping on various physical properties of single crystals of MoSe2

    Institute of Scientific and Technical Information of China (English)

    MihirM. Vora; Aditya M. Vora

    2012-01-01

    Effect of rhenium doping is examined in single crystals of MoSe2 viz.MoRe0.005Se1.995,MoRe0.001Se1.999 and Mo0.995Re0.005Se2,which is grown by using the direct vapor transport (DVT) technique.The grown crystals are structurally characterized by X-ray diffraction,by determining their lattice parameters a and c,and X-ray density.Also,the Hall effect and thermoelectric power (TEP) measurements show that the single crystals exhibit a p-type semiconducting nature.The direct and indirect band gap measurements are also undertaken on these semiconducting materials.

  4. Spectral properties and shielding behavior of gamma irradiated MoO{sub 3}-doped silicophosphate glasses

    Energy Technology Data Exchange (ETDEWEB)

    Hamdy, Y.M., E-mail: yousry_m_h@yahoo.com [Spectroscopy Department, Physics Division, National Research Center, Dokki, Cairo (Egypt); Marzouk, M.A.; ElBatal, H.A. [Glass Research Department, National Research Center, Dokki, Cairo (Egypt)

    2013-11-15

    Combined optical and infrared absorption spectra of prepared molybdenum ions in sodium silicophosphate host glasses were investigated before and after gamma irradiation with a dose of 8 Mrad (8×10{sup 4} Gy). The undoped base sodium silicophosphate glass reveals strong charge transfer ultraviolet absorption but with no visible bands. This strong UV absorption is related to the presence of contaminated trace iron impurities (mainly Fe{sup 3+} ions) within the raw materials used for the preparation of this host glass. The MoO{sub 3} doped glasses exhibit extra characteristic absorption bands due to the presence of molybdenum ions in three possible valence states, the trivalent, pentavalent and hexavalent forms. Gamma irradiation of the base undoped glass increases the extension of optical absorption within the UV spectrum and produces an extra broad visible band centered at 520 nm. Such radiation-induced spectra are interpreted by assuming the formation of new induced color centers through the absorption of released electrons and formed positive holes during the irradiation process. Also, the possible formation of induced centers through photochemical transformation of some Fe{sup 2+} ions to Fe{sup 3+} ions by accepting positive holes. The presence of molybdenum ions is assumed to compete with the suggested irradiation reactions by capturing electrons and positive holes during the irradiation process. Infrared absorption spectra of the undoped and MoO{sub 3}-doped glasses reveal broad IR vibrational bands which are attributed to the presence of combined characteristic vibrational IR modes due to main phosphate and partner silicate groups. The addition of MoO{sub 3} (0.5–1.5%) as dopant level causes no changes in the number and position of the main characteristic absorption bands. Gamma irradiation did not cause any marked changes in the IR spectra and the maintainance of the same main IR bands due to the stability of the network containing dual compact two glass

  5. Effect of monolayer supports on the electronic structure of single-layer MoS2

    Science.gov (United States)

    Ramirez-Torres, Alfredo; Le, Duy; Rahman, Talat S.

    2015-03-01

    We present results of density functional theory based calculations of the electronic structure of a single-layer of MoS2, as modified by three different single-layer materials used as support: hexagonal boron nitride (h-BN), graphene, and silicene, using the local density approximation (LDA), on the one hand, and a functional that explicitly includes van der Waals interactions (optB88-vdW), on the other hand. Because the lattice mismatch between the primitive cell of MoS2 and those of the supports is large, calculations are performed with as large a supercell as computationally feasible, so as to reduce the incommensurability between lattices. Even though van der Waals interactions are expected to play an important role in the binding between MoS2, and h-BN and graphene, we find that the band structure and related conclusions obtained by optB88-vdW and LDA are quite similar for the three heterostructures considered here. Single-layer MoS2 interacts weakly with h-BN and graphene, while covalent bonds are formed with silicene. Detailed analysis of the electronic density of states also indicates little effect of h-BN and graphene, while silicene severely modifies it by introducing additional states within the band gap. Furthermore, adsorption on graphene brings the conduction bands of MoS2 down to the Fermi level of graphene as a result of charge transfer from graphene to MoS2, while adsorption on silicene shifts both valence and conduction bands towards the Fermi level, in addition to inducing a gap of ~50 meV in silicene itself.

  6. Measurement of target and double-spin asymmetries for the e<mo>→>p<mo>→mo><mo>→mo>eπ<mo>+mo><mo>(n)> reaction in the nucleon resonance region at low Q2

    Energy Technology Data Exchange (ETDEWEB)

    Zheng, X.; Adhikari, K. P.; Bosted, P.; Deur, A.; Drozdov, V.; El Fassi, L.; Kang, Hyekoo; Kovacs, K.; Kuhn, S.; Long, E.; Phillips, S. K.; Ripani, M.; Slifer, K.; Smith, L. C.; Adikaram, D.; Akbar, Z.; Amaryan, M. J.; Anefalos Pereira, S.; Asryan, G.; Avakian, H.; Badui, R. A.; Ball, J.; Baltzell, N. A.; Battaglieri, M.; Batourine, V.; Bedlinskiy, I.; Biselli, A. S.; Briscoe, W. J.; Bültmann, S.; Burkert, V. D.; Carman, D. S.; Celentano, A.; Chandavar, S.; Charles, G.; Chen, J. -P.; Chetry, T.; Choi, Seonho; Ciullo, G.; Clark, L.; Colaneri, L.; Cole, P. L.; Compton, N.; Contalbrigo, M.; Crede, V.; D' Angelo, A.; Dashyan, N.; De Vita, R.; De Sanctis, E.; Djalali, C.; Dodge, G. E.; Dupre, R.; Egiyan, H.; El Alaoui, A.; Elouadrhiri, L.; Eugenio, P.; Fanchini, E.; Fedotov, G.; Fersch, R.; Filippi, A.; Fleming, J. A.; Gevorgyan, N.; Ghandilyan, Y.; Gilfoyle, G. P.; Giovanetti, K. L.; Girod, F. X.; Gleason, C.; Golovach, E.; Gothe, R. W.; Griffioen, K. A.; Guidal, M.; Guler, N.; Guo, L.; Hanretty, C.; Harrison, N.; Hattawy, M.; Hicks, K.; Holtrop, M.; Hughes, S. M.; Ilieva, Y.; Ireland, D. G.; Ishkhanov, B. S.; Isupov, E. L.; Jenkins, D.; Jiang, H.; Jo, H. S.; Joosten, S.; Keller, D.; Khachatryan, G.; Khandaker, M.; Kim, A.; Kim, W.; Klein, F. J.; Kubarovsky, V.; Lanza, L.; Lenisa, P.; Livingston, K.; MacGregor, I. J. D.; Markov, N.; McKinnon, B.; Mirazita, M.; Mokeev, V.; Movsisyan, A.; Munevar, E.; Munoz Camacho, C.; Murdoch, G.; Nadel-Turonski, P.; Net, L. A.; Ni, A.; Niccolai, S.; Niculescu, G.; Niculescu, I.; Osipenko, M.; Ostrovidov, A. I.; Paolone, M.; Paremuzyan, R.; Park, K.; Pasyuk, E.; Peng, P.; Pisano, S.; Pogorelko, O.; Price, J. W.; Puckett, A. J. R.; Raue, B. A.; Rizzo, A.; Rosner, G.; Rossi, P.; Roy, P.; Sabatié, F.; Salgado, C.; Schumacher, R. A.; Sharabian, Y. G.; Skorodumina, Iu.; Smith, G. D.; Sokhan, D.; Sparveris, N.; Stankovic, I.; Strakovsky, I. I.; Strauch, S.; Taiuti, M.; Tian, Ye; Ungaro, M.; Voskanyan, H.; Voutier, E.; Walford, N. K.; Watts, D. P.; Wei, X.; Weinstein, L. B.; Wood, M. H.; Zachariou, N.; Zhang, J.; Zonta, I.

    2016-10-01

    We report measurements of target- and double-spin asymmetries for the exclusive channel e<mo>→>p<mo>→mo><mo>→mo>eπ<mo>+mo><mo>(n)> in the nucleon resonance region at Jefferson Lab using the CEBAF Large Acceptance Spectrometer (CLAS). These asymmetries were extracted from data obtained using a longitudinally polarized NH3 target and a longitudinally polarized electron beam with energies 1.1, 1.3, 2.0, 2.3, and 3.0 GeV. The new results are consistent with previous CLAS publications but are extended to a low Q2 range from 0.0065 to 0.35 (GeV/c)2. The Q2 access was made possible by a custom-built Cherenkov detector that allowed the detection of electrons for scattering angles as low as 6 degrees. These results are compared with the unitary isobar models JANR and MAID, the partial-wave analysis prediction from SAID, and the dynamic model DMT. In many kinematic regions our results, in particular results on the target asymmetry, help to constrain the polarization-dependent components of these models.

  7. Polarization-dependent photocurrent in MoS2 phototransistor

    Science.gov (United States)

    Li, Jiu; Yu, Wentao; Chu, Saisai; Yang, Hong; Shi, Kebin; Gong, Qihuang

    2015-03-01

    Monolayer or few-layer molybdenum disulfide (MoS2) has attracted increasing interests in studying light-induced electronic effect due to its prominent photo-responsivity at visible spectral range, fast photo-switching rate and high channel mobility. However, the atomically thin layers make the interaction between light and matter much weaker than that in bulk state, hampering its application in two-dimensional material optoelectronics. One of recent efforts was to utilize resonantly enhanced localized surface plasmon for boosting light-matter interaction in MoS2 thin layer phototransistor. Randomly deposited metallic nano-particles were previously reported to modify surface of a back-gated MoS2 transistor for increasing light absorption cross-section of the phototransistor. Wavelength-dependent photocurrent enhancement was observed. In this paper, we report on a back-gated multilayer MoS2 field-effect-transistor (FET), whose surface is decorated with oriented gold nanobar array, of which the size of a single nanobar is 60nm:60nm:120nm. With these oriented nanostructures, photocurrent of the MoS2 FET could be successfully manipulated by a linear polarized incident 633nm laser, which fell into the resonance band of nanobar structure. We find that the drain-source current follows cos2θ relationship with respect to the incident polarization angle. We attribute the polarization modulation effect to the localized enhancement nature of gold nanobar layer, where the plasmon enhancement occurs only when the polarization of incident laser parallels to the longitudinal axis of nanobars and when the incident wavelength matches the resonance absorption of nanobars simultaneously. Our results indicate a promising application of polarization-dependent plasmonic manipulation in two-dimension semiconductor materials and devices.

  8. Reduction of nitric oxide with carbon monoxide on the Al-Mo(110) surface alloy

    Science.gov (United States)

    Grigorkina, G. S.; Tvauri, I. V.; Kaloeva, A. G.; Burdzieva, O. G.; Sekiba, D.; Ogura, S.; Fukutani, K.; Magkoev, T. T.

    2016-05-01

    Coadsorption and reaction of carbon monoxide (CO) and nitric oxide (NO) on Al-Mo(110) surface alloy have been studied by means of Auger electron, reflection-absorption infrared and temperature programmed desorption spectroscopies (AES, RAIRS, TPD), low energy electron diffraction (LEED) and work function measurements. The Al-Mo(110) surface alloy was obtained by thermal annealing at 800 K of aluminum film deposited on Mo(110) held at room temperature. Upon annealing Al penetrates the surface, most likely forming stoichiometric hexagonal surface monolayer of the compound Al2Mo. The NO and CO adsorb molecularly on this alloy surface at 200 K, unlike totally dissociative adsorption on bare Mo(110) and Al(111) film. Adsorption of CO on NO precovered Al-Mo(110) substrate dramatically affects the state of NO molecules, most probably displacing them to higher-coordinated sites with their simultaneous tilting to the surface plane. Heating to about room temperature (320 K) causes reduction of nitric oxide with carbon monoxide, yielding CO2, and substrate nitridation. This behavior can be associated with the surface reconstruction providing additional Al/Mo interface reaction sites and change of the d-band upon alloying.

  9. Pr16Mo21O56

    Directory of Open Access Journals (Sweden)

    Patrick Gougeon

    2011-05-01

    Full Text Available The structure of hexadecapraseodymium henicosamolybdenum hexapentacontaoxide, Pr16Mo21O56, is isotypic with other rare earth representatives of formula type RE16Mo21O56 (RE = La, Ce, Nd. It is characterized by Mo10O18iO8a units (where i = inner and a = apical O atoms containing bioctahedral Mo10 clusters and octahedral MoO6 units that share some of their O atoms to form the Mo–O framework. The two independent Mo10 cluster units are centred at Wyckoff positions 2b and 2c and have point-group symmetry overline{1}. The Mo atom of the MoO6 unit is likewise situated at an inversion centre (2d. The eight crystallographically different Pr3+ cations occupy irregular voids in the framework with coordination numbers to the O atoms varying between 8 and 11.

  10. New molybdenum(VI) phosphates: synthesis, characterization, and calculations of centrosymmetric RbMoO2PO4 and noncentrosymmetric Rb4Mo5P2O22.

    Science.gov (United States)

    Wang, Ying; Pan, Shilie; Su, Xin; Yang, Zhihua; Dong, Lingyun; Zhang, Min

    2013-02-04

    Two new molybdenum(VI) phosphates, RbMoO(2)PO(4) and Rb(4)Mo(5)P(2)O(22), have been synthesized by standard solid-state reactions, and their structures were determined by single-crystal X-ray diffraction. The former is centrosymmetric, whereas the latter is noncentrosymmetric and chiral. Their crystal structures both consist of corner- and edge-shared MoO(6) octahedra, PO(4) tetrahedra, and RbO(n) (n = 8 or 10) polyhedra and exhibit three- and one-dimensional structures, respectively. Powder second-harmonic generation (SHG) measurements revealed an SHG efficiency of approximately 1.4 × KH(2)PO(4) (KDP) for Rb(4)Mo(5)P(2)O(22). Thermal analysis, infrared and UV-vis-NIR diffuse reflectance spectroscopy, and electronic band structure calculations were also performed on the reported materials. Crystal data are the following: RbMoO(2)PO(4), orthorhombic, space group Fddd (No. 70), a = 11.012(5) Å, b = 12.403(5) Å, c = 15.839(7) Å, V = 2163.3(16) Å(3), and Z = 16; Rb(4)Mo(5)P(2)O(22), orthorhombic, space group C222(1) (No. 20), a = 6.5300(5) Å, b = 19.7834(18) Å, c = 17.3451(15) Å, V = 2240.7(3) Å(3), and Z = 4.

  11. A theoretical modeling of photocurrent generation and decay in layered MoS2 thin-film transistor photosensors

    Science.gov (United States)

    Hur, Ji-Hyun; Park, Junghak; Jeon, Sanghun

    2017-02-01

    A model that universally describes the characteristics of photocurrent in molybdenum disulphide (MoS2) thin-film transistor (TFT) photosensors in both ‘light on’ and ‘light off’ conditions is presented for the first time. We considered possible material-property dependent carrier generation and recombination mechanisms in layered MoS2 channels with different numbers of layers. We propose that the recombination rates that are mainly composed of direct band-to-band recombination and interface trap-involved recombination change on changing the light condition and the number of layers. By comparing the experimental results, it is shown that the model performs well in describing the photocurrent behaviors of MoS2 TFT photosensors, including the photocurrent generation under illumination and a hugely long time persistent trend of the photocurrent decay in the dark condition, for a range of MoS2 layer numbers.

  12. Stretch Band Exercise Program

    Science.gov (United States)

    Skirka, Nicholas; Hume, Donald

    2007-01-01

    This article discusses how to use stretch bands for improving total body fitness and quality of life. A stretch band exercise program offers a versatile and inexpensive option to motivate participants to exercise. The authors suggest practical exercises that can be used in physical education to improve or maintain muscular strength and endurance,…

  13. ZEBRAFISH CHROMOSOME-BANDING

    NARCIS (Netherlands)

    PIJNACKER, LP; FERWERDA, MA

    1995-01-01

    Banding techniques were carried out on metaphase chromosomes of zebrafish (Danio rerio) embryos. The karyotypes with the longest chromosomes consist of 12 metacentrics, 26 submetacentrics, and 12 subtelocentrics (2n = 50). All centromeres are C-band positive. Eight chromosomes have a pericentric C-b

  14. Optimization of the Processing of Mo Disks

    Energy Technology Data Exchange (ETDEWEB)

    Tkac, Peter [Argonne National Lab. (ANL), Argonne, IL (United States); Rotsch, David A. [Argonne National Lab. (ANL), Argonne, IL (United States); Stepinski, Dominique [Argonne National Lab. (ANL), Argonne, IL (United States); Makarashvili, Vakhtang [Argonne National Lab. (ANL), Argonne, IL (United States); Harvey, James [NorthStar Medical Technologies, LLC, Madison, WI (United States); Vandegrift, George F. [Argonne National Lab. (ANL), Argonne, IL (United States)

    2016-01-01

    The objective of this work is to decrease the processing time for irradiated disks of enriched Mo for the production of 99Mo. Results are given for the dissolution of nonirradiated Mo disks, optimization of the process for large-scale dissolution of sintered disks, optimization of the removal of the main side products (Zr and Nb) from dissolved targets, and dissolution of irradiated Mo disks.

  15. Hall and Nernst effects in monolayer MoS2

    Science.gov (United States)

    Zhang, Yun-Hai; Zhang, Ming-Hua

    2016-03-01

    We study Hall and Nernst transports in monolayer MoS2 based on Green’s function formalism. We have derived analytical results for spin and valley Hall conductivities in the zero temperature and spin and valley Nernst conductivities in the low temperature. We found that tuning of the band gap and spin-orbit splitting can drive system transition from spin Hall insulator (SHI) to valley Hall insulator (VHI). When the system is subjected to a temperature gradient, the spin and valley Nernst conductivities are dependent on Berry curvature.

  16. Progressive Band Selection

    Science.gov (United States)

    Fisher, Kevin; Chang, Chein-I

    2009-01-01

    Progressive band selection (PBS) reduces spectral redundancy without significant loss of information, thereby reducing hyperspectral image data volume and processing time. Used onboard a spacecraft, it can also reduce image downlink time. PBS prioritizes an image's spectral bands according to priority scores that measure their significance to a specific application. Then it uses one of three methods to select an appropriate number of the most useful bands. Key challenges for PBS include selecting an appropriate criterion to generate band priority scores, and determining how many bands should be retained in the reduced image. The image's Virtual Dimensionality (VD), once computed, is a reasonable estimate of the latter. We describe the major design details of PBS and test PBS in a land classification experiment.

  17. Highly Uniform Wafer-scale Synthesis of α-MoOsub>3sub> by Plasma Enhanced Chemical Vapor Deposition.

    Science.gov (United States)

    Kim, HyeongU; Son, Juhyun; Kulkarni, Atul; Ahn, Chisung; Kim, Ki Seok; Shin, Dongjoo; Yeom, Geun; Kim, Taesung

    2017-03-20

    Molybdenum oxide (MoOsub>3sub>) has gained immense attention because of its high electron mobility, wide band gap, and excellent optical and catalytic properties. However, the synthesis of uniform and large-area MoOsub>3sub> is challenging. Here, we report the synthesis of wafer-scale α-MoO3 by plasma oxidation of Mo-deposited on Si/SiOsub>2sub>. Mo was oxidized by Osub>2sub> plasma in a plasma enhanced chemical vapor deposition (PECVD) system at 150 °C. Mo was oxidized by Osub>2sub> plasma in a PECVD system at 150 °C. It was found that the synthesized α-MoOsub>3sub> had a highly uniform crystalline structure. For the as-synthesized α-MoOsub>3sub> sensor, we observed a current change when the relative humidity was increased from 11% to 95%. The sensor was exposed to different humidity levels with fast recovery time of about 8 s. Hence this feasibility study shows that MoOsub>3sub> synthesized at low temperature can be utilized for the gas sensing applications by adopting flexible device technology.

  18. QTAIM analysis of the bonding in Mo-Mo bonded dimolybdenum complexes.

    Science.gov (United States)

    Van der Maelen, Juan F; Cabeza, Javier A

    2012-07-02

    A number of local and integral topological parameters of the electron density of relevant bonding interactions in the binuclear molybdenum complexes [Mo(2)Cl(8)](4-), [Mo(2)(μ-CH(3)CO(2))(4)], [Mo(2)(μ-CF(3)CO(2))(4)], [Mo(2)(μ-CH(3)CO(2))(4)Br(2)](2-), [Mo(2)(μ-CF(3)CO(2))(4)Br(2)](2-), [Mo(2)(μ-CH(3)CO(2))(2)Cl(4)](2-), [Mo(2)(μ-CH(3)CO(2))(2)(μ-Cl)(2)Cl(4)](2-), and [Mo(2)(μ-Cl)(3)Cl(6)](3-) have been calculated and interpreted under the perspective of the quantum theory of atoms in molecules (QTAIM). These data have allowed a comparison between related but different atom-atom interactions, such as different Mo-Mo formal bond orders, ligand-unbridged versus Cl-bridged, CH(3)CO(2)-bridged, and CF(3)CO(2)-bridged Mo-Mo interactions, and Mo-Cl(terminal) and Mo-Cl(bridge) versus Mo-Br and Mo-O interactions. Calculations carried out using nonrelativistic and relativistic approaches afforded similar results.

  19. Anisotropy of optical absorption and luminescent properties of CaMoO{sub 4}

    Energy Technology Data Exchange (ETDEWEB)

    Zakharko, Ya., E-mail: zakharko@electronics.wups.lviv.u [Faculty of Electronics, Ivan Franko National University of Lviv, 107 Tarnavskogo St., 79017 Lviv (Ukraine); Luchechko, A. [Faculty of Electronics, Ivan Franko National University of Lviv, 107 Tarnavskogo St., 79017 Lviv (Ukraine); Syvorotka, I.; Stryganyuk, G.; Solskii, I. [Institute for Materials, SRC ' Carat' , 202 Stryjska St., 79031 Lviv (Ukraine)

    2010-03-15

    Optical absorption, excitation and emission spectra, as well as photoluminescence decay time of CaMoO{sub 4} single crystals have been measured. It has been revealed that annealing of crystals in oxygen atmosphere leads to the disappearance of their anisotropic behavior in optical absorption, as well as in X-ray luminescence and decay time. Moreover, it has been found that annealing can significantly affect the value of the decay time. The relative intensity of the long-wavelength emission band increases under excitation in the region of indirect band-to-band transitions.

  20. Thickness-Dependent Binding Energy Shift in Few-Layer MoS2 Grown by Chemical Vapor Deposition.

    Science.gov (United States)

    Lin, Yu-Kai; Chen, Ruei-San; Chou, Tsu-Chin; Lee, Yi-Hsin; Chen, Yang-Fang; Chen, Kuei-Hsien; Chen, Li-Chyong

    2016-08-31

    The thickness-dependent surface states of MoS2 thin films grown by the chemical vapor deposition process on the SiO2-Si substrates are investigated by X-ray photoelectron spectroscopy. Raman and high-resolution transmission electron microscopy suggest the thicknesses of MoS2 films to be ranging from 3 to 10 layers. Both the core levels and valence band edges of MoS2 shift downward ∼0.2 eV as the film thickness increases, which can be ascribed to the Fermi level variations resulting from the surface states and bulk defects. Grainy features observed from the atomic force microscopy topographies, and sulfur-vacancy-induced defect states illustrated at the valence band spectra imply the generation of surface states that causes the downward band bending at the n-type MoS2 surface. Bulk defects in thick MoS2 may also influence the Fermi level oppositely compared to the surface states. When Au contacts with our MoS2 thin films, the Fermi level downshifts and the binding energy reduces due to the hole-doping characteristics of Au and easy charge transfer from the surface defect sites of MoS2. The shift of the onset potentials in hydrogen evolution reaction and the evolution of charge-transfer resistances extracted from the impedance measurement also indicate the Fermi level varies with MoS2 film thickness. The tunable Fermi level and the high chemical stability make our MoS2 a potential catalyst. The observed thickness-dependent properties can also be applied to other transition-metal dichalcogenides (TMDs), and facilitates the development in the low-dimensional electronic devices and catalysts.

  1. Strain engineering in monolayer WS2, MoS2, and the WS2/MoS2 heterostructure

    KAUST Repository

    He, Xin

    2016-10-27

    Mechanically exfoliated monolayers of WS2, MoS2 and their van der Waals heterostructure were fabricated on flexible substrate so that uniaxial tensile strain can be applied to the two-dimensional samples. The modification of the band structure under strain was investigated by micro-photoluminescence spectroscopy at room temperature as well as by first-principles calculations. Exciton and trion emissions were observed in both WS2 and the heterostructure at room temperature, and were redshifted by strain, indicating potential for applications in flexible electronics and optoelectronics.

  2. Optimal Designs of Ultra Wide-band Communication Antennas

    Institute of Scientific and Technical Information of China (English)

    JIYicai; LIUQizhong; HEXiulian; ZHANGHou

    2004-01-01

    A novel design approach combining the Hybrid genetic algorithm (HGA) with Method of moment (MoM) is investigated for the fast optimal design of ultra wide-band loaded wire antennas. A simple filtrating procedure is used to reduce the number of the loads and the components of the loading circuits, thus making the manufacture and experimental adjustment of the antennas easier, and the reliability of the antennas enhanced. The effectivity of the proposed procedure is demonstrated through its application to the optimal design of an ultra wide-band antenna.

  3. Robust effective Zeeman energy in monolayer MoS2 quantum dots

    Science.gov (United States)

    Dias, A. C.; Fu, Jiyong; Villegas-Lelovsky, L.; Qu, Fanyao

    2016-09-01

    We report a theoretical investigation on the energy spectrum and the effective Zeeman energy (EZE) in monolayer MoS2 circular quantum dots, subjected to an out-of-plane magnetic field. Interestingly, we observe the emergence of energy-locked modes, depending on the competition between the dot confinement and the applied magnetic field, for either the highest K-valley valence band or the lowest {{K}\\prime} -valley conduction band. Moreover, an unusual dot-size-independent EZE behavior of the highest valence and the lowest conduction bands is found. Although the EZEs are insensitive to the variation of quantum confinement, both of them grow linearly with the magnetic field, similar to that in the monolayer MoS2 material. The EZEs along with their ‘robustness’ against dot confinements open opportunities of a universal magnetic control over the valley degree of freedom, for quantum dots of all sizes.

  4. Synthesis of hierarchical MoO2/MoS2 nanofibers for electrocatalytic hydrogen evolution

    Science.gov (United States)

    Rheem, Youngwoo; Han, Yosep; Lee, Kyu Hwan; Choi, Sung-Mook; Myung, Nosang V.

    2017-03-01

    Perpendicularly attached MoS2 nanosheets on MoO2 conductive nanofibers were synthesized by combining electrospinning, calcination, and sulfurization processes. Compared to randomly stacked MoS2 nanosheets on MoO2 nanofiber, they show greater hydrogen evolution reaction (HER) performance (i.e., onset potential of ‑180 mV versus normal hydrogen electrode with the Tafel slope of 59 mV dec‑1). HER performance decreases with increasing MoS2 nanocrystal size.

  5. Visible-light photocatalytic properties of Mo-C codoped anatase TiO2 films prepared by magnetron sputtering

    Science.gov (United States)

    Zhe-Peng, Zhang; Biao, Yu; Hai-Bo, Fan; Xin-Liang, Zheng; He-Bao, Yao

    2015-12-01

    A range of different contents of Mo-C codoped TiO2 films were sputtered by using home-made Mo-C codoped TiO2 targets, which were sintered by mixing the Mo2C and TiO2 powder with different mole ratio. We found that the Mo and C ions were successfully incorporated into the lattice of TiO2 films. As a result, the band gap of TiO2 was reduced and the visible-light photocatalytic property was enhanced. The photocatalytic performance of Mo-C codoped TiO2 films was strictly relevant with the band gap and there was a best codoping concentration of 0.01% for the TiO2 film, which processed the smallest band gap and the best photocatalytic property. If the codoping concentration increased, the photocatalytic performance decreased dramatically. Our results suggest that sputtering technique is a convenient method to prepare Mo-C codoped TiO2 films with tunable doping content and high photocatalytic performance.

  6. First-principles study of the structural and electronic properties of graphene/MoS2 interfaces

    Science.gov (United States)

    Hieu, Nguyen Ngoc; Phuc, Huynh Vinh; Ilyasov, Victor V.; Chien, Nguyen D.; Poklonski, Nikolai A.; Van Hieu, Nguyen; Nguyen, Chuong V.

    2017-09-01

    In this paper, we study the structural and electronic properties of graphene adsorbed on MoS2 monolayer (G/MoS2) with different stacking configurations using dispersion-corrected density functional theory. Our calculations show that the interaction between graphene and MoS2 monolayer is a weak van der Waals interaction in all four stacking configurations with the binding energy per carbon atom of -30 meV. In the presence of MoS2 monolayer, the linear bands on the Dirac cone of graphene at the interfaces are slightly split. A band gap about 3 meV opens in G/MoS2 interfaces due to the breaking of sublattice symmetry by the intrinsic interface dipole, and it could be effectively modulated by the stacking configurations. Furthermore, we found that an n-type Schottky contact is formed at the G/MoS2 interface in all four stacking configurations with a small Schottky barrier about 0.49 eV. The appearance of the non-zero band gap in graphene has opened up new possibilities for its application in electronic devices such as graphene field-effect transistors.

  7. MoS2 and semiconductors in the flatland

    Directory of Open Access Journals (Sweden)

    Oleg V. Yazyev

    2015-01-01

    Full Text Available The fascinating properties of graphene, the first two-dimensional (2D material, and the accompanying strong activity in the research community have sparked a renewed interest in related layered crystalline materials with unique electronic and optical properties. Their superb mechanical properties, optical transparency, direct band gap and large degree of electrostatic control due to their atomic scale thickness make them interesting inorganic nanosystems for a wide variety of applications. In this review we will present a short history of research in the synthesis, band properties and potential applications of 2D semiconductors with a particular emphasis on MoS2, the prototypical and best-studied material from this family.

  8. Iliotibial band friction syndrome.

    Science.gov (United States)

    Lavine, Ronald

    2010-07-20

    Published articles on iliotibial band friction syndrome have been reviewed. These articles cover the epidemiology, etiology, anatomy, pathology, prevention, and treatment of the condition. This article describes (1) the various etiological models that have been proposed to explain iliotibial band friction syndrome; (2) some of the imaging methods, research studies, and clinical experiences that support or call into question these various models; (3) commonly proposed treatment methods for iliotibial band friction syndrome; and (4) the rationale behind these methods and the clinical outcome studies that support their efficacy.

  9. Van der Waals Epitaxy of Two-Dimensional MoS2-Graphene Heterostructures in Ultrahigh Vacuum.

    Science.gov (United States)

    Miwa, Jill A; Dendzik, Maciej; Grønborg, Signe S; Bianchi, Marco; Lauritsen, Jeppe V; Hofmann, Philip; Ulstrup, Søren

    2015-06-23

    In this work, we demonstrate direct van der Waals epitaxy of MoS2-graphene heterostructures on a semiconducting silicon carbide (SiC) substrate under ultrahigh vacuum conditions. Angle-resolved photoemission spectroscopy (ARPES) measurements show that the electronic structure of free-standing single-layer (SL) MoS2 is retained in these heterostructures due to the weak van der Waals interaction between adjacent materials. The MoS2 synthesis is based on a reactive physical vapor deposition technique involving Mo evaporation and sulfurization in a H2S atmosphere on a template consisting of epitaxially grown graphene on SiC. Using scanning tunneling microscopy, we study the seeding of Mo on this substrate and the evolution from nanoscale MoS2 islands to SL and bilayer (BL) MoS2 sheets during H2S exposure. Our ARPES measurements of SL and BL MoS2 on graphene reveal the coexistence of the Dirac states of graphene and the expected valence band of MoS2 with the band maximum shifted to the corner of the Brillouin zone at K̅ in the SL limit. We confirm the 2D character of these electronic states via a lack of dispersion with photon energy. The growth of epitaxial MoS2-graphene heterostructures on SiC opens new opportunities for further in situ studies of the fundamental properties of these complex materials, as well as perspectives for implementing them in various device schemes to exploit their many promising electronic and optical properties.

  10. Plasma nanocoating of thiophene onto MoS{sub 2} nanotubes

    Energy Technology Data Exchange (ETDEWEB)

    Türkaslan, Banu Esencan [Suleyman Demirel University, Faculty of Engineering, Department of Chemical Engineering, 32260 Isparta (Turkey); Dikmen, Sibel [Suleyman Demirel University, Faculty of Arts and Science, Department of Chemistry, 32260 Isparta (Turkey); Öksüz, Lütfi [Suleyman Demirel University, Faculty of Arts and Science, Department of Physics, 32260 Isparta (Turkey); Öksüz, Aysegul Uygun, E-mail: ayseguluygun@sdu.edu.tr [Suleyman Demirel University, Faculty of Arts and Science, Department of Chemistry, 32260 Isparta (Turkey)

    2015-12-01

    Highlights: • MoS{sub 2} nanotubes were coated with thiophene by atmospheric pressure radio-frequency (RF) glow discharge. • Among nanohybrid preparation methods, the plasma methods appear as new technology. • The effect of plasma power on PTh/MoS{sub 2} nanocomposite properties has been investigated. • When the discharge power is increased between 117 and 360 W the chemical structure of PTh is not changed and the structure of nanocomposites become more uniformly. - Abstract: MoS{sub 2} nanotubes were coated with conductive polymer thiophene by atmospheric pressure radio-frequency (RF) glow discharge. MoS{sub 2} nanotubes were prepared by thermal decomposition of hexadecylamine (HDA) intercalated laminar MoS{sub 2} precursor on anodized aluminum oxide template and the thiophene was polymerized directly on surface of these nanotubes as in situ by plasma method. The effect of plasma power on PTh/MoS{sub 2} nanocomposite properties has been investigated by means of Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM and EDX), and X-ray diffraction spectroscopy (XRD). The presence of PTh bands in the FTIR spectra of PTh/MoS{sub 2} nanotube nanocomposites corresponding XRD results indicates that the polythiophene coating onto MoS{sub 2} nanotube. The chemical structure of PTh is not changed when the plasma power of discharge differ from 117 to 360 W. SEM images of nanocomposites show that when the discharge power is increased between 117 and 360 W the average diameter of PTh/MoS{sub 2} nanotube nanocomposites are changed and the structure become more uniformly.

  11. 4-d magnetism: Electronic structure and magnetism of some Mo-based alloys

    Science.gov (United States)

    Liu, Yong; Bose, S. K.; Kudrnovský, J.

    2017-02-01

    We report results of a first-principles density-functional study of alloys of the 4 d -element Mo with group IV elements Si, Ge and Sn in zinc blende (ZB) and rock salt (RS) structures. The study was motivated by a similar study of ours based on the 4 d -element Tc, which showed the presence of half-metallic states with integer magnetic moment (1μB) per formula unit in TcX (X=C, Si, Ge) alloys. The calculated Curie temperatures for the ferromagnetic (FM) phases were low, around or less than 300 K. Searching for the possibility of 4 d -based alloys with higher Curie temperatures we have carried out the study involving the elements Mo, Ru and Rh. Among these the most promising case appears to be that involving the element Mo. Among the MoX (X=Si, Ge, Sn) alloys in ZB and RS structures, both MoGe and MoSn in ZB structures are found to possess an integer magnetic moment of 2μB per formula unit. ZB MoSn can be classified as a marginal/weak half-metal or a spin gapless semiconductor, while ZB MoGe would be best described as a gapless magnetic semiconductor. The calculated Curie temperatures are in the range 300-700 K. Considering the theoretical uncertainty in the band gaps due not only to the treatment of exchange and correlation effects, but density functional theory itself, these classifications may change somewhat, but both merit investigation from the viewpoint of potential spintronic application. Based on their higher Curie temperatures, Mo-based alloys would serve such purpose better than the previously reported Tc-based ones.

  12. Co-precipitation synthesis and characterization of faceted MoS{sub 2} nanorods with controllable morphologies

    Energy Technology Data Exchange (ETDEWEB)

    Vattikuti, S.V.P.; Byon, Chan; Reddy, C.V.; Shim, Jaesool [Yeungnam University, School of Mechanical Engineering, Gyeongsan (Korea, Republic of); Venkatesh, B. [Vardhaman College of Engineering, Department of Mechanical Engineering, Kacharam, Hyderabad (India)

    2015-06-15

    Molybdenum disulfide (MoS{sub 2}) nanopowder has been prepared using a co-precipitation method. This paper describes the thermal effect on the morphology enhancement of MoS{sub 2} sphere-like structures into nanorods with a winding structure. For the reduction in precursors, the as-obtained MoS{sub 2} nanopowder was calcinated at 250, 400, 600, and 800 C for 1 h in an N{sub 2} environment. The calcined samples were characterized using a particle size analyzer, X-ray diffraction, Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy with X-ray analysis (EDAX) and transmission electron microscopy, HRTEM and X-ray photoelectron spectroscopy. The results show the MoS{sub 2} sphere-like structure with diameter in the range of 50-100 nm and rod-like winding structure with diameter in the range of 20-150 nm, and a few tens of micrometers in length with a high degree of size homogeneity. The FT-IR spectra show the obtained bands at 480 and 900 cm{sup -1} are corresponding to the Mo-S bond and the S-S bond. The TG-DTA curves confirm the thermal stability of the prepared samples. It is observed that the band gap energy for the MoS{sub 2} nanorods is lower than for the nanospherical structure MoS{sub 2}, which leads to achieve high electron and hole recombination rate. (orig.)

  13. Sensing Properties of Gas Sensor Based on Adsorption of NO2 with Defect, Pristine, Fe and Si-MoS2 Layer

    Directory of Open Access Journals (Sweden)

    S.R. Shakil

    2014-11-01

    Full Text Available Two-dimensional (2D layered materials are currently being considered as entrant for future electronic devices. Molybdenum disulphide (MoS2 belongs to a family of layered transitional metal dichalcogenides(TMDS,has a unique characteristics of showing intrinsic semiconducting nature is being considered a major advantageous over graphene (which has no intrinsic band gap as a two-dimensional (2D channel material in field effect transistors(FET. In the paper, the results of investigations are presented concerning the affects of adsorption of NO2 gas on the surface of MoS2, defect-MoS2, Si-MoS2 and Fe-MoS2 layer. The changes density of states (DOS and electrostatic difference potential of Si-MoS2 by applying different gate voltage were studied. We proposed that, NO2 might play an important role on MoS2 layer that can be used as gas sensor. In the research, it has been shown that in the case of gas sensor, the adsorption of NO2 with MoS2, Fe-MoS2, Si-MoS2 and defect-MoS2 play an important rule for sensing behavior.

  14. Tunable band gap photoluminescence from atomically thin transition-metal dichalcogenide alloys.

    Science.gov (United States)

    Chen, Yanfeng; Xi, Jinyang; Dumcenco, Dumitru O; Liu, Zheng; Suenaga, Kazu; Wang, Dong; Shuai, Zhigang; Huang, Ying-Sheng; Xie, Liming

    2013-05-28

    Band gap engineering of atomically thin two-dimensional (2D) materials is the key to their applications in nanoelectronics, optoelectronics, and photonics. Here, for the first time, we demonstrate that in the 2D system, by alloying two materials with different band gaps (MoS2 and WS2), tunable band gap can be obtained in the 2D alloys (Mo(1-x)W(x)S(2) monolayers, x = 0-1). Atomic-resolution scanning transmission electron microscopy has revealed random arrangement of Mo and W atoms in the Mo(1-x)W(x)S(2) monolayer alloys. Photoluminescence characterization has shown tunable band gap emission continuously tuned from 1.82 eV (reached at x = 0.20) to 1.99 eV (reached at x = 1). Further, density functional theory calculations have been carried out to understand the composition-dependent electronic structures of Mo(1-x)W(x)S(2) monolayer alloys.

  15. Diet after gastric banding

    Science.gov (United States)

    ... helps people who have a gastric band stay satisfied longer. This includes things like salad with grilled ... ADAM Health Solutions. About MedlinePlus Site Map FAQs Customer Support Get email updates Subscribe to RSS Follow ...

  16. MoS2 spaser

    Science.gov (United States)

    Jayasekara, Charith; Premaratne, Malin; Gunapala, Sarath D.; Stockman, Mark I.

    2016-04-01

    We present a comprehensive analysis of a spaser made of a circular shaped highly doped molybdenum disulfide (MoS2) resonator. "Spaser" is an acronym for "surface plasmon amplification by stimulated emission of radiation"-a nanoscale source of surface plasmons generated by stimulated emission in a plasmonic resonator which receives energy nonradiatively. By considering localized surface plasmon modes, operation characteristics of the model are analysed, and tunability of the design is demonstrated. We find the optimum geometric and material parameters of the spaser that provides efficient outputs and carryout a comparative analysis with a similar circular spaser made of graphene. Owing to physical and chemical properties of MoS2 and the active medium, the proposed design delivers efficient outputs in terms of spaser mode energy, operating thresholds, Q-factor, and electric field amplitude. Lower operating thresholds and higher mode energies are notable advantages of the design. Owing to having many superior features to existing similar designs, this MoS2 spaser may be much suited for applications in nanoplasmonic devices.

  17. Excitation dependent bidirectional electron transfer in phthalocyanine-functionalised MoS2 nanosheets.

    Science.gov (United States)

    Nguyen, Emily P; Carey, Benjamin J; Harrison, Christopher J; Atkin, Paul; Berean, Kyle J; Della Gaspera, Enrico; Ou, Jian Zhen; Kaner, Richard B; Kalantar-Zadeh, Kourosh; Daeneke, Torben

    2016-09-15

    Two-dimensional (2D) transition metal chalcogenides such as 2D MoS2 are considered prime candidate materials for the design of next generation optoelectronics. Functionalisation of these materials is considered to be a key step in tailoring their properties towards specific applications and unlocking their full potential. Here we present a van der Waals functionalisation strategy for creating MoS2 nanosheets decorated with free base phthalocyanine chromophores. The semiconducting sheets are found to intimately interact with these optoelectronically active chromophores, resulting in an electronic heterostructure that exhibits enhanced optoelectronic properties and exploitable charge transfer. We show that by utilising laterally confined MoS2 nanosheets, the conduction band of the semiconductor could be positioned between the chromophore's S1 and S2 states. Consequently, bidirectional photoinduced electron transfer processes are observed, with excitation of the functionalised nanosheet's semiconductor transition resulting in electron transfer to the phthalocyanine's LUMO, and excitation of the chromophore's S2 state leading to electron injection into the MoS2 conduction band. However, charge transfer from the dye's S1 transition to the MoS2 nanosheet is found to be thermodynamically unfavourable, resulting in intense radiative recombination. These findings may enable controlling and tuning the charge carrier density of semiconducting nanosheets via optical means through the exploitation of photoinduced electron transfer. Furthermore this work provides access to 2D semiconductor-hybrids with tailored absorption profiles and photoluminescence.

  18. Effect of biaxial strain and external electric field on electronic properties of MoS2 monolayer: A first-principle study

    Science.gov (United States)

    Nguyen, Chuong V.; Hieu, Nguyen N.

    2016-04-01

    In this work, making use of density functional theory (DFT) computations, we systematically investigate the effect of biaxial strain engineering and external electric field applied perpendicular to the layers on the band gaps and electronic properties of monolayer MoS2. The direct-to-indirect band gaps and semiconductor-to-metal transition are observed in monolayer MoS2 when strain and electric field are applied in our calculation. We show that when the biaxial strain and external electric field are introduced, the electronic properties including band gaps of monolayer MoS2 can be reduced to zero. Our results provide many useful insights for the wide applications of monolayer MoS2 in electronics and optoelectronics.

  19. HYBASE - HYperspectral BAnd SElection tool

    NARCIS (Netherlands)

    Schwering, P.B.W.; Bekman, H.H.P.T.; Seijen, H.H. van

    2008-01-01

    Band selection is essential in the design of multispectral sensor systems. This paper describes the TNO hyperspectral band selection tool HYBASE. It calculates the optimum band positions given the number of bands and the width of the spectral bands. HYBASE is used to calculate the minimum number of

  20. MoSi2 oxidation resistance coatings for Mo5Si3/MoSi2 composites

    Institute of Scientific and Technical Information of China (English)

    YAN Jianhui; XU Hongmei; ZHANG Houan; TANG Siwen

    2009-01-01

    In order to improve the oxidation resistance properties of 30 at.% Mo5Si3/MoSi2 composite at high temperature in air, a molybdenum disili-tide coating was prepared on its surface by a molten salt technology. XRD and SEM analysis showed that only tetragonal MoSi2 phase ex-isted in the coating after being siliconized for 5 h at 900℃. The oxidation film formed on the uncoated sample was not dense, so that oxygen diffused easily through it. The volatilization of MoO3 resulted in the oxidation film separating from the substrate. The MoSi2coating was proved to be an effective method to prevent 30 at.% MosSi3/MoSi2 composites from being oxidized at 1200℃. A dense glassy SiO2 film was formed on the MoSi2 coating surface, which acted as a barrier layer for the diffusion of oxygen atoms to the substrate. The 30at.% Mo5Si3/MoSi2 composites with a MoSi2 coating showed much better oxidation resistance at high temperature.

  1. Lithium Intercalation in Graphene/MoS2 Composites: First-Principles Insights

    CERN Document Server

    Shao, Xiji; Pang, Rui; Shi, Xingqiang

    2015-01-01

    As a storage material for Li-ion batteries, graphene/molybdenum disulfide (Gr/MoS2) composites have been intensively studied in experiments. But the relevant theoretical works from first-principles are lacking. In the current work, van-der-Waals-corrected density functional theory calculations are performed to investigate the interaction of Li in Gr/MoS2 composites. Three interesting features are revealed for the intercalated Gr/Li(n)/MoS2 composites (n = 1 to 9). One is the reason for large Li storage capacity of Gr/MoS2: due to the binding energies per Li atom increase with the increasing number of intercalated Li atoms. Secondly, the band gap opening of Gr is found, and the band gap is enlarged with the increasing number of intercalated Li atoms, up to 160 meV with nine Li; hence these results suggest an efficient way to tune the band gap of graphene. Thirdly, the Dirac cone of Gr always preserve for different number of ionic bonded Li atoms.

  2. Engineering MoSx/Ti/InP Hybrid Photocathode for Improved Solar Hydrogen Production

    Science.gov (United States)

    Li, Qiang; Zheng, Maojun; Zhong, Miao; Ma, Liguo; Wang, Faze; Ma, Li; Shen, Wenzhong

    2016-07-01

    Due to its direct band gap of ~1.35 eV, appropriate energy band-edge positions, and low surface-recombination velocity, p-type InP has attracted considerable attention as a promising photocathode material for solar hydrogen generation. However, challenges remain with p-type InP for achieving high and stable photoelectrochemical (PEC) performances. Here, we demonstrate that surface modifications of InP photocathodes with Ti thin layers and amorphous MoSx nanoparticles can remarkably improve their PEC performances. A high photocurrent density with an improved PEC onset potential is obtained. Electrochemical impedance analyses reveal that the largely improved PEC performance of MoSx/Ti/InP is attributed to the reduced charge-transfer resistance and the increased band bending at the MoSx/Ti/InP/electrolyte interface. In addition, the MoSx/Ti/InP photocathodes function stably for PEC water reduction under continuous light illumination over 2 h. Our study demonstrates an effective approach to develop high-PEC-performance InP photocathodes towards stable solar hydrogen production.

  3. Topological Nonsymmorphic Metals from Band Inversion

    Science.gov (United States)

    Muechler, Lukas; Alexandradinata, A.; Neupert, Titus; Car, Roberto

    2016-10-01

    We expand the phase diagram of two-dimensional, nonsymmorphic crystals at integer fillings that do not guarantee gaplessness. In addition to the trivial, gapped phase that is expected, we find that band inversion leads to a class of topological, gapless phases. These topological phases are exemplified by the monolayers of M Te2 (M =W ,Mo ) if spin-orbit coupling is neglected. We characterize the Dirac band touching of these topological metals by the Wilson loop of the non-Abelian Berry gauge field. Furthermore, we develop a criterion for the proximity of these topological metals to 2D and 3D Z2 topological insulators when spin-orbit coupling is included; our criterion is based on nonsymmorphic symmetry eigenvalues, and may be used to identify topological materials without inversion symmetry. An additional feature of the Dirac cone in monolayer M Te2 is that it tilts over in a Lifshitz transition to produce electron and hole pockets—a type-II Dirac cone. These pockets, together with the pseudospin structure of the Dirac electrons, suggest a unified, topological explanation for the recently reported, nonsaturating magnetoresistance in WTe2 , as well as its circular dichroism in photoemission. We complement our analysis and first-principles band structure calculations with an ab-initio-derived tight-binding model for the WTe2 monolayer.

  4. Topological Nonsymmorphic Metals from Band Inversion

    Directory of Open Access Journals (Sweden)

    Lukas Muechler

    2016-12-01

    Full Text Available We expand the phase diagram of two-dimensional, nonsymmorphic crystals at integer fillings that do not guarantee gaplessness. In addition to the trivial, gapped phase that is expected, we find that band inversion leads to a class of topological, gapless phases. These topological phases are exemplified by the monolayers of MTe_{2} (M=W,Mo if spin-orbit coupling is neglected. We characterize the Dirac band touching of these topological metals by the Wilson loop of the non-Abelian Berry gauge field. Furthermore, we develop a criterion for the proximity of these topological metals to 2D and 3D Z_{2} topological insulators when spin-orbit coupling is included; our criterion is based on nonsymmorphic symmetry eigenvalues, and may be used to identify topological materials without inversion symmetry. An additional feature of the Dirac cone in monolayer MTe_{2} is that it tilts over in a Lifshitz transition to produce electron and hole pockets—a type-II Dirac cone. These pockets, together with the pseudospin structure of the Dirac electrons, suggest a unified, topological explanation for the recently reported, nonsaturating magnetoresistance in WTe_{2}, as well as its circular dichroism in photoemission. We complement our analysis and first-principles band structure calculations with an ab-initio-derived tight-binding model for the WTe_{2} monolayer.

  5. New high-pressure phases of MoSe2 and MoTe2

    Science.gov (United States)

    Kohulák, Oto; MartoÅák, Roman

    2017-02-01

    Three Mo-based transition-metal dichalcogenides MoS2,MoSe2, and MoTe2 share at ambient conditions the same structure 2 Hc , consisting of layers where Mo atoms are surrounded by six chalcogen atoms in trigonal prism coordination. The knowledge of their high-pressure behavior is, however, limited, particularly in case of MoSe2 and MoTe2. The latter materials do not undergo a layer-sliding transition 2 Hc→ 2 Ha known in MoS2 and currently no other stable phase aside from 2 Hc is known in these systems at room temperature. Employing evolutionary crystal structure prediction in combination with ab initio calculations, we study the zero-temperature phase diagram of both materials up to Mbar pressures. We find a tetragonal phase with space group P4/mmm, previously predicted in MoS2, to become stable in MoSe2 at 118 GPa. In MoTe2, we predict at 50 GPa a transition to a new layered tetragonal structure with space group I4/mmm, similar to CaC2, where Mo atoms are surrounded by eight Te atoms. The phase is metallic already at the transition pressure and becomes a good metal beyond 1 Mbar. We discuss chemical trends in the family of Mo-based transition-metal dichalcogenides and suggest that MoTe2 likely offers the easiest route towards the post-2 H phases.

  6. Role of interlayer coupling in ultra thin MoS 2

    KAUST Repository

    Cheng, Yingchun

    2012-01-01

    The effects of interlayer coupling on the vibrational and electronic properties of ultra thin MoS 2 were studied by ab initio calculations. For smaller slab thickness, the interlayer distance is significantly elongated because of reduced interlayer coupling. This explains the anomalous thickness dependence of the lattice vibrations observed by Lee et al. (ACS Nano, 2010, 4, 2695). The absence of interlayer coupling in mono-layer MoS 2 induces a transition from direct to indirect band gap behaviour. Our results demonstrate a strong interplay between the intralayer chemical bonding and the interlayer van-der-Waals interaction. This journal is © 2012 The Royal Society of Chemistry.

  7. First Principles Study on Electronic Structures of Mn2+:CdMoO4 Crystals

    Institute of Scientific and Technical Information of China (English)

    WANG Xi-En; LIU Ting-Yu; ZHANG Qi-Ren; ZHANG Hai-Yan; SONG Min; GUO Xiao-Feng; YIN Ji-Gang

    2008-01-01

    @@ Electronic structures of the Mn2+:CdMoO4 crystal are studied within the framework of the fully relativistic self-consistent Dirac-Slater theory,using a numerically discrete variation (DV-Xα)method.The calculated results indicate that the 3d states of Mn have donor energy level in the forbidden band of CdMoO4 crystal.The transition energy of O 2p→Mn 3d is 3.12 eV under excitation corresponding electronic transition being O2-+Mn2+ hvex=3.12 eV→ O-+Mn+hvem→O2+Mn2+.

  8. Unexpected strong magnetism of Cu doped single-layer MoS₂ and its origin.

    Science.gov (United States)

    Yun, Won Seok; Lee, J D

    2014-05-21

    The magnetism of the 3d transition-metal (TM) doped single-layer (1L) MoS2, where the Mo atom is partially replaced by the 3d TM atom, is investigated using the first-principles density functional calculations. In a series of 3d TM doped 1L-MoS2's, the induced spin polarizations are negligible for Sc, Ti, and Cr dopings, while the induced spin polarizations are confirmed for V, Mn, Fe, Co, Ni, Cu, and Zn dopings and the systems become magnetic. Especially, the Cu doped system shows unexpectedly strong magnetism although Cu is nonmagnetic in its bulk state. The driving force is found to be a strong hybridization between Cu 3d states and 3p states of neighboring S, which results in an extreme unbalanced spin-population in the spin-split impurity bands near the Fermi level. Finally, we also discuss further issues of the Cu induced magnetism of 1L-MoS2 such as investigation of additional charge states, the Cu doping at the S site instead of the Mo site, and the Cu adatom on the layer (i.e., 1L-MoS2).

  9. Vacuum ultraviolet radiation effects on two-dimensional MoS2 field-effect transistors

    Science.gov (United States)

    McMorrow, Julian J.; Cress, Cory D.; Arnold, Heather N.; Sangwan, Vinod K.; Jariwala, Deep; Schmucker, Scott W.; Marks, Tobin J.; Hersam, Mark C.

    2017-02-01

    Atomically thin MoS2 has generated intense interest for emerging electronics applications. Its two-dimensional nature and potential for low-power electronics are particularly appealing for space-bound electronics, motivating the need for a fundamental understanding of MoS2 electronic device response to the space radiation environment. In this letter, we quantify the response of MoS2 field-effect transistors (FETs) to vacuum ultraviolet (VUV) total ionizing dose radiation. Single-layer (SL) and multilayer (ML) MoS2 FETs are compared to identify differences that arise from thickness and band structure variations. The measured evolution of the FET transport properties is leveraged to identify the nature of VUV-induced trapped charge, isolating the effects of the interface and bulk oxide dielectric. In both the SL and ML cases, oxide trapped holes compete with interface trapped electrons, exhibiting an overall shift toward negative gate bias. Raman spectroscopy shows no variation in the MoS2 signatures as a result of VUV exposure, eliminating significant crystalline damage or oxidation as possible radiation degradation mechanisms. Overall, this work presents avenues for achieving radiation-hard MoS2 devices through dielectric engineering that reduces oxide and interface trapped charge.

  10. Dynamic Memory Cells Using MoS2 Field-Effect Transistors Demonstrating Femtoampere Leakage Currents.

    Science.gov (United States)

    Kshirsagar, Chaitanya U; Xu, Weichao; Su, Yang; Robbins, Matthew C; Kim, Chris H; Koester, Steven J

    2016-09-27

    Two-dimensional semiconductors such as transition-metal dichalcogenides (TMDs) are of tremendous interest for scaled logic and memory applications. One of the most promising TMDs for scaled transistors is molybdenum disulfide (MoS2), and several recent reports have shown excellent performance and scalability for MoS2 MOSFETs. An often overlooked feature of MoS2 is that its wide band gap (1.8 eV in monolayer) and high effective masses should lead to extremely low off-state leakage currents. These features could be extremely important for dynamic memory applications where the refresh rate is the primary factor affecting the power consumption. Theoretical predictions suggest that leakage currents in the 10(-18) to 10(-15) A/μm range could be possible, even in scaled transistor geometries. Here, we demonstrate the operation of one- and two-transistor dynamic memory circuits using MoS2 MOSFETs. We characterize the retention times in these circuits and show that the two-transistor memory cell reveals MoS2 MOSFETs leakage currents as low as 1.7 × 10(-15) A/μm, a value that is below the noise floor of conventional DC measurements. These results have important implications for the future use of MoS2 MOSFETs in low-power circuit applications.

  11. Photoelectron imaging spectroscopy of MoC{sup −} and NbN{sup −} diatomic anions: A comparative study

    Energy Technology Data Exchange (ETDEWEB)

    Liu, Qing-Yu; Li, Zi-Yu; He, Sheng-Gui, E-mail: shengguihe@iccas.ac.cn, E-mail: chenh@iccas.ac.cn [Beijing National Laboratory for Molecular Sciences, State Key Laboratory for Structural Chemistry of Unstable and Stable Species, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190 (China); Hu, Lianrui; Chen, Hui, E-mail: shengguihe@iccas.ac.cn, E-mail: chenh@iccas.ac.cn [Beijing National Laboratory for Molecular Sciences, Key Laboratory of Photochemistry, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190 (China); Ning, Chuan-Gang [Department of Physics, State Key Laboratory of Low-Dimensional Quantum Physics, Tsinghua University, Beijing 100084 (China); Ma, Jia-Bi [Key Laboratory of Cluster Science, The Institute for Chemical Physics, School of Chemistry, Beijing Institute of Technology, Beijing 100081 (China)

    2015-04-28

    The isoeletronic diatomic MoC{sup −} and NbN{sup −} anions have been prepared by laser ablation and studied by photoelectron imaging spectroscopy combined with quantum chemistry calculations. The photoelectron spectra of NbN{sup −} can be very well assigned on the basis of literature reported optical spectroscopy of NbN. In contrast, the photoelectron spectra of MoC{sup −} are rather complex and the assignments suffered from the presence of many electronically hot bands and limited information from the reported optical spectroscopy of MoC. The electron affinities of NbN and MoC have been determined to be 1.450 ± 0.003 eV and 1.360  ±  0.003 eV, respectively. The good resolution of the imaging spectroscopy provided a chance to resolve the Ω splittings of the X{sup 3}Σ{sup −} (Ω = 0 and 1) state of MoC and the X{sup 4}Σ{sup −} (Ω = 1/2 and 3/2) state of MoC{sup −} for the first time. The spin-orbit splittings of the X{sup 2}Δ state of NbN{sup −} and the a{sup 2}Δ state of MoC{sup −} were also determined. The similarities and differences between the electronic structures of the NbN and MoC systems were discussed.

  12. Harvesting, storing and utilising solar energy using MoO3 : modulating structural distortion through pH adjustment.

    Science.gov (United States)

    Lou, Shi Nee; Ng, Yun Hau; Ng, Charlene; Scott, Jason; Amal, Rose

    2014-07-01

    Nanostructured molybdenum oxide (α-MoO3 ) thin film photoelectrodes were synthesised by anodisation. Upon band gap-excitation by light illumination, α-MoO3 is able to store a portion of the excited charges in its layered structure with the simultaneous intercalation of alkali cations. The stored electrons can be discharged from α-MoO3 for utilisation under dark conditions, and α-MoO3 is able to recharge itself with successive illuminations to behave as a 'self-photo-rechargeable' alkali-ion battery. The alteration of the anodisation pH allowed the crystal structure and oxygen vacancy concentrations of α-MoO3 to be modulated to achieve (i) a distorted MoO6 octahedra for enhanced charge separation and storage, (ii) a layered structure with a greater exposed (010) crystal face for rich and reversible ion intercalation and (iii) a highly crystalline thin film that suppresses electron-hole pair recombination. Overall, the larger MoO6 octahedral distortion in α-MoO3 at a higher pH favours charge storage, whereas smaller octahedral distortion at a lower pH leads to anodic photocurrent enhancement.

  13. Photonic band gap materials

    Science.gov (United States)

    Cassagne, D.

    Photonic band gap materials Photonic band gap materials are periodic dielectric structures that control the propagation of electromagnetic waves. We describe the plane wave method, which allows to calculate the band structures of photonic crystals. By symmetry analysis and a perturbative approach, we predict the appearance of the low energy photonic band gaps of hexagonal structures. We propose new two-dimensional structures called graphite and boron nitride. Using a transfer matrix method, we calculate the transmission of the graphite structure and we show the crucial role of the coupling with external modes. We study the appearance of allowed modes in the photonic band gap by the introduction of localized defects in the periodicity. Finally, we discuss the properties of opals formed by self-organized silica microspheres, which are very promising for the fabrication of three-dimensional photonic crystals. Les matériaux à bandes interdites photoniques sont des structures diélectriques périodiques qui contrôlent la propagation des ondes électromagnétiques. Nous décrivons la méthode des ondes planes qui permet de calculer les structures de bandes des cristaux photoniques. Par une analyse de la symétrie et une approche perturbative, nous précisons les conditions d'existence des bandes interdites de basse énergie. Nous proposons de nouvelles structures bidimensionnelles appelées graphite et nitrure de bore. Grâce à une méthode de matrices de transfert, nous calculons la transmission de la structure graphite et nous mettons en évidence le rôle fondamental du couplage avec les modes extérieurs. Nous étudions l'apparition de modes permis dans la bande interdite grâce à l'introduction de défauts dans la périodicité. Enfin, nous discutons les propriétés des opales constituées de micro-billes de silice auto-organisées, qui sont très prometteuses pour la fabrication de cristaux photoniques tridimensionnels.

  14. Distribution Free Prediction Bands

    CERN Document Server

    Lei, Jing

    2012-01-01

    We study distribution free, nonparametric prediction bands with a special focus on their finite sample behavior. First we investigate and develop different notions of finite sample coverage guarantees. Then we give a new prediction band estimator by combining the idea of "conformal prediction" (Vovk et al. 2009) with nonparametric conditional density estimation. The proposed estimator, called COPS (Conformal Optimized Prediction Set), always has finite sample guarantee in a stronger sense than the original conformal prediction estimator. Under regularity conditions the estimator converges to an oracle band at a minimax optimal rate. A fast approximation algorithm and a data driven method for selecting the bandwidth are developed. The method is illustrated first in simulated data. Then, an application shows that the proposed method gives desirable prediction intervals in an automatic way, as compared to the classical linear regression modeling.

  15. Electron scattering from 92Mo

    Science.gov (United States)

    Milliman, T. E.; Connelly, J. P.; Heisenberg, J. H.; Hersman, F. W.; Wise, J. E.; Papanicolas, C. N.

    1990-06-01

    Differential cross sections for electron scattering from 92Mo have been measured for excitation energies less than 5.1 MeV over a range of momentum transfer of 0.5 to 3.1 fm-1. The elastic scattering data are analyzed along with existing electron and muonic atom data to provide an improved description of the ground-state charge distribution. The inelastic scattering data have been analyzed to extract electromagnetic transition densities. These densities are interpreted in terms of the underlying nuclear structure.

  16. Olympus Turbo MO 640SII

    Institute of Scientific and Technical Information of China (English)

    蔡翰林

    2001-01-01

    @@ 此款由Olympus推出的TurboMO 640 SII,外观上,以全机身乳白色的优美色调,配合简洁的控制面板;规格上,可读取最大达640MB容量的磁盘片并可向下兼容.在众多的硬件中又多了一台美观实用的MO光盘机可供使用者选择.

  17. Endoscopic band ligation for bleeding lesions in the small bowel.

    Science.gov (United States)

    Ikeya, Takashi; Ishii, Naoki; Shimamura, Yuto; Nakano, Kaoru; Ego, Mai; Nakamura, Kenji; Takagi, Koichi; Fukuda, Katsuyuki; Fujita, Yoshiyuki

    2014-10-16

    To investigate the safety and efficacy of endoscopic band ligation (EBL) for bleeding lesions in the small bowel. This is a retrospective study evaluating EBL in six consecutive patients (three males, three females, 46-86 years of age) treated between May 2009 and February 2014: duodenal vascular ectasia; 1, jejunal bleeding diverticulum; 1, ileal Dieulafoy's lesion; 1 and ileal bleeding diverticula; 3. The success of the initial hemostasis was evaluated, and patients were observed for early rebleeding (within 30 d after EBL), and complications such as perforation and abscess formation. Follow-up endoscopies were performed in four patients. Initial hemostasis was successfully achieved with EBL in all six patients. Eversion was not sufficient in four diverticular lesions. Early rebleeding occurred three days after EBL in one ileal diverticulum, and a repeat endoscopy revealed dislodgement of the O-band and ulcer formation at the banded site. This rebleeding was managed conservatively. Late rebleeding occurred in this case (13 and 21 mo after initial EBL), and re-EBL was performed. Follow-up endoscopies revealed scar formation and the disappearance of vascular lesions at the banded site in the case with a duodenal bleeding lesion, and unresolved ileal diverticula in three cases. Surgery or transarterial embolization was not required without any complications during the median follow-up period of 45 (range, 2-83) mo. EBL is a safe and effective endoscopic treatment for hemostasis of bleeding lesions in the small bowel.

  18. Ultra wide band antennas

    CERN Document Server

    Begaud, Xavier

    2013-01-01

    Ultra Wide Band Technology (UWB) has reached a level of maturity that allows us to offer wireless links with either high or low data rates. These wireless links are frequently associated with a location capability for which ultimate accuracy varies with the inverse of the frequency bandwidth. Using time or frequency domain waveforms, they are currently the subject of international standards facilitating their commercial implementation. Drawing up a complete state of the art, Ultra Wide Band Antennas is aimed at students, engineers and researchers and presents a summary of internationally recog

  19. Banded transformer cores

    Science.gov (United States)

    Mclyman, C. W. T. (Inventor)

    1974-01-01

    A banded transformer core formed by positioning a pair of mated, similar core halves on a supporting pedestal. The core halves are encircled with a strap, selectively applying tension whereby a compressive force is applied to the core edge for reducing the innate air gap. A dc magnetic field is employed in supporting the core halves during initial phases of the banding operation, while an ac magnetic field subsequently is employed for detecting dimension changes occurring in the air gaps as tension is applied to the strap.

  20. Orthorhombic MoO3 nanobelts based NO2 gas sensor

    Science.gov (United States)

    Mane, A. A.; Moholkar, A. V.

    2017-05-01

    Molybdenum trioxide (MoO3) nanobelts have been deposited onto the glass substrates using chemical spray pyrolysis (CSP) deposition method. The XRD patterns reveal that films are polycrystalline having an orthorhombic crystal structure. Raman spectra confirm that the films are orthorhombic in phase. The XPS study shows the presence of two well resolved spectral lines of Mo-3d core levels appearing at the binding energy values of 232.82 eV and 235.95 eV corresponding to Mo-3d5/2 and Mo-3d3/2, respectively. These binding energy values are assigned to Mo6+ oxidation state of fully oxidized MoO3. The FE-SEM micrographs show the formation of nanobelts-like morphology. The AFM micrographs reveal that the RMS surface roughness increases from 16.5 nm to 17.5 nm with increase in film thickness from 470 nm to 612 nm and then decreases to 16 nm for 633 nm film thickness. The band gap energy is found to be decreased from 3.40 eV to 3.38 eV. To understand the electronic transport phenomenon in MoO3 thin films, dielectric properties are studied. For 612 nm film thickness, the highest NO2 gas response of 68% is obtained at an operating temperature of 200 °C for 100 ppm concentration with response and recovery times of 15 s and 150 s, respectively. The lower detection limit is found to be 10 ppm which is half of the immediately dangerous to life or health (IDLH) value of 20 ppm. Finally, NO2 gas sensing mechanism in an orthorhombic MoO3 crystal structure is discussed in detail.

  1. Hot-wire vapor deposition of amorphous MoS{sub 2} thin films

    Energy Technology Data Exchange (ETDEWEB)

    Papadimitropoulos, Georgios; Kontos, A.; Vasilopoulou, Maria; Kouvatsos, Dimitrios N.; Boukos, Nicolas; Davazoglou, Dimitrios [Institute of Nanoscience and Nanotechnology, NCSR ' ' Demokritos' ' , Attiki (Greece); Vourdas, Nikolaos [Technological Educational Institute of Chalkis (Greece); Gasparotto, Alberto [Department of Chemistry, Padova University (Italy); INSTM, Padova (Italy); Barreca, Davide [CNR-IENI, Padova (Italy); INSTM, Padova (Italy); Department of Chemistry, Padova University (Italy)

    2015-07-15

    Amorphous, as shown by X-ray diffraction measurements, MoS{sub 2} films (a-MoS{sub 2}) were deposited by heating a molybdenum wire at temperatures between 500 and 700 C in H{sub 2}S at 1 Torr. As shown by Scanning Electron Microscopy measurements, the morphology of samples depends significantly on the filament temperature; at low temperature samples are homogeneous and smooth, at intermediate temperatures they exhibit a granular microstructure and at high temperatures a columnar one. X-ray photoelectron spectroscopy measurements have shown S/Mo ratios in films varying between 2.5 and 1.5 dependent on filament temperature. Films also contain oxygen at atomic contents of 8 to 12%. As shown by XPS and Raman spectroscopy, at a filament temperature of 600 C films are mainly composed of MoS{sub 2} also containing oxygen at an atomic ratio of 8%. Spectroscopic ellipsometry measurements made on a-MoS{sub 2} films have shown that their band gap is of the order of 1.4 eV, slightly higher than that for the bulk crystalline material. Photoluminescence spectroscopy measurements have shown that samples exhibit a doublet of peaks at 2.8 and 3 eV blue shifted relatively to MoS{sub 2} samples composed of one or two mono-layers. The above indicate that the electronic structure of crystalline atomic-layer thick MoS{sub 2} is preserved in a-MoS{sub 2} films. (copyright 2015 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  2. Thermodynamic Analysis of Electrodeposited Ni-Mo and Ni-Mo-P Alloys

    Institute of Scientific and Technical Information of China (English)

    GUO Zhong-cheng; XU Rui-dong; WANG Ji-kun

    2004-01-01

    The potential-pH diagram of Ni-P-H2O system is calculated and constructed by use of thermodynamic data. On the basis of the potential-pH diagram the electrochemical behaviors of electrodepositing Ni-Mo and Ni-Mo-P alloys are analyzed. The phases of Ni-Mo and Ni-Mo-P coatings are identified by means of X-ray diffraction analysis. The thermodynamic analysis shows that it is difficult to deposit Mo or P individually from its aqueous solution, and they must be co-deposited with other metals by induced deposition; P and Ni can be deposited as compound Ni3P on the cathode; Mo is deposited in two forms: one is in the form of MoO3 solid particles and the other is in the form of compound MoC. X-ray diffraction analysis is in agreement with the thermodynamic analysis.

  3. Origin of the n -type and p -type conductivity of MoS 2 monolayers on a SiO 2 substrate

    KAUST Repository

    Dolui, Kapildeb

    2013-04-02

    Ab initio density functional theory calculations are performed to study the electronic properties of a MoS2 monolayer deposited over a SiO 2 substrate in the presence of interface impurities and defects. When MoS2 is placed on a defect-free substrate, the oxide plays an insignificant role since the conduction band top and the valence band minimum of MoS2 are located approximately in the middle of the SiO2 band gap. However, if Na impurities and O dangling bonds are introduced at the SiO2 surface, these lead to localized states, which modulate the conductivity of the MoS2 monolayer from n- to p-type. Our results show that the conductive properties of MoS2 deposited on SiO 2 are mainly determined by the detailed structure of the MoS 2/SiO2 interface, and suggest that doping the substrate can represent a viable strategy for engineering MoS2-based devices. © 2013 American Physical Society.

  4. Mo99 Production Plant Layout

    Energy Technology Data Exchange (ETDEWEB)

    Woloshun, Keith Albert [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Dale, Gregory E. [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Naranjo, Angela Carol [Los Alamos National Lab. (LANL), Los Alamos, NM (United States)

    2015-06-25

    The NorthStar Medical Technologies 99Mo production facility configuration is envisioned to be 8 accelerator pairs irradiating 7 100Mo targets (one spare accelerator pair undergoing maintenance while the other 7 pairs are irradiating targets). The required shielding in every direction for the accelerators is initially estimated to be 10 feet of concrete. With the accelerator pairs on one (ground) level and spaced with the required shielding between adjacent pairs, the only practical path for target insertion and removal while minimizing floor space is vertical. The current scheme then requires a target vertical lift of nominally 10 feet through a shield stack. It is envisioned that the lift will be directly into a hot cell where an activated target can be removed from its holder and a new target attached and lowered. The hot cell is on a rail system so that a single hot cell can service all active target locations, as well as deliver the ready targets to the separations lab. On this rail system, coupled to the hot cell, will be a helium recovery and clean-up system. All helium coolant equipment is located on the upper level near to the target removal point.

  5. An investigation of the optical properties and water splitting potential of the coloured metallic perovskites Sr1-xBaxMoO3

    Science.gov (United States)

    Hopper, H. A.; Le, J.; Cheng, J.; Weller, T.; Marschall, R.; Bloh, J. Z.; Macphee, D. E.; Folli, A.; Mclaughlin, A. C.

    2016-02-01

    The solid solution Sr1-xBaxMoO3 (x=0.00, 0.025, 0.050, 0.075, 0.100 and 1.00) has been synthesised. Rietveld refinement of X-ray diffraction data shows that all materials crystallise with cubic (Pm-3m) symmetry and that a miscibility gap exists from x=0.1-1.0. The optical properties of the metallic perovskites Sr1-xBaxMoO3 have been investigated by a combination of UV-vis spectroscopy and density functional theory (DFT). Upon increasing x from 0 to 1 in Sr1-xBaxMoO3 there is a reduction in the measured band gap from 2.20 eV to 2.07 eV. The measured band gap is attributed to the electronic transition from the Mo 4d t2g band to the eg band. The potential of SrMoO3 and BaMoO3 as water-splitting photocatalysts was explored but there was no evidence of hydrogen or oxygen evolution, even with the presence of a Pt co-catalyst.

  6. Pressure coefficients for direct optical transitions in MoS2, MoSe2, WS2, and WSe2 crystals and semiconductor to metal transitions.

    Science.gov (United States)

    Dybała, F; Polak, M P; Kopaczek, J; Scharoch, P; Wu, K; Tongay, S; Kudrawiec, R

    2016-05-24

    The electronic band structure of MoS2, MoSe2, WS2, and WSe2, crystals has been studied at various hydrostatic pressures experimentally by photoreflectance (PR) spectroscopy and theoretically within the density functional theory (DFT). In the PR spectra direct optical transitions (A and B) have been clearly observed and pressure coefficients have been determined for these transitions to be: αA = 2.0 ± 0.1 and αB = 3.6 ± 0.1 meV/kbar for MoS2, αA = 2.3 ± 0.1 and αB = 4.0 ± 0.1 meV/kbar for MoSe2, αA = 2.6 ± 0.1 and αB = 4.1 ± 0.1 meV/kbar for WS2, αA = 3.4 ± 0.1 and αB = 5.0 ± 0.5 meV/kbar for WSe2. It has been found that these coefficients are in an excellent agreement with theoretical predictions. In addition, a comparative study of different computational DFT approaches has been performed and analyzed. For indirect gap the pressure coefficient have been determined theoretically to be -7.9, -5.51, -6.11, and -3.79, meV/kbar for MoS2, MoSe2, WS2, and WSe2, respectively. The negative values of this coefficients imply a narrowing of the fundamental band gap with the increase in hydrostatic pressure and a semiconductor to metal transition for MoS2, MoSe2, WS2, and WSe2, crystals at around 140, 180, 190, and 240 kbar, respectively.

  7. Exceptionally large banded spherulites

    Science.gov (United States)

    Lagasse, R. R.

    1994-07-01

    This article concerns the crystallization of maleic anhydride from a blend containing 2 wt% of poly(acrylonitrile). High speed photography and temperature measurements during the crystallization as well as X-ray diffraction from the blend after crystallization are consistent with a banded spherulitic morphology.

  8. Colloquium: Topological band theory

    Science.gov (United States)

    Bansil, A.; Lin, Hsin; Das, Tanmoy

    2016-04-01

    The first-principles band theory paradigm has been a key player not only in the process of discovering new classes of topologically interesting materials, but also for identifying salient characteristics of topological states, enabling direct and sharpened confrontation between theory and experiment. This review begins by discussing underpinnings of the topological band theory, which involve a layer of analysis and interpretation for assessing topological properties of band structures beyond the standard band theory construct. Methods for evaluating topological invariants are delineated, including crystals without inversion symmetry and interacting systems. The extent to which theoretically predicted properties and protections of topological states have been verified experimentally is discussed, including work on topological crystalline insulators, disorder and interaction driven topological insulators (TIs), topological superconductors, Weyl semimetal phases, and topological phase transitions. Successful strategies for new materials discovery process are outlined. A comprehensive survey of currently predicted 2D and 3D topological materials is provided. This includes binary, ternary, and quaternary compounds, transition metal and f -electron materials, Weyl and 3D Dirac semimetals, complex oxides, organometallics, skutterudites, and antiperovskites. Also included is the emerging area of 2D atomically thin films beyond graphene of various elements and their alloys, functional thin films, multilayer systems, and ultrathin films of 3D TIs, all of which hold exciting promise of wide-ranging applications. This Colloquium concludes by giving a perspective on research directions where further work will broadly benefit the topological materials field.

  9. Edge termination of MoS2 and CoMoS catalyst particles

    DEFF Research Database (Denmark)

    Byskov, Line Sjolte; Nørskov, Jens Kehlet; Clausen, B. S.;

    2000-01-01

    The edge termination of MoS2 and CoMoS catalyst particles is studied by density functional calculations. We show that for structures without vacancies Mo-terminated edges have the lowest edge energies. Creation of vacancies, which are believed to be active sites in these catalyst systems, leads...

  10. Determination of crystallization as a function of Mo layer thickness in Mo/Si multilayers

    DEFF Research Database (Denmark)

    Abdali, Salim; Gerward, Leif; Yakshin, A.E.;

    2002-01-01

    Mo/Si multilayer samples with different Mo layer thickness were deposited by electron beam evaporation, while Kr+ ions (300 eV) were used for polishing the Si layers. Crystallization as a function of the Mo layer thickness deposited was investigated by grazing incidence X-ray diffraction, giving...

  11. DUAL BAND MONOPOLE ANTENNA DESIGN

    Directory of Open Access Journals (Sweden)

    P. Jithu

    2013-06-01

    Full Text Available The WLAN and Bluetooth applications become popular in mobile devices, integrating GSM and ISM bands operation in one compact antenna, can reduce the size of mobile devices. Recently, lot many investigations are carried out in designing a dual band antennas with operating frequencies in GSM band and in ISM band for mobile devices. Printed monopoles are under this investigation. In this paper, dual-band printed monopoles are presented to operate at GSM band i.e. 900 MHz and ISM band i.e. 2.4 GHz. We intend to observe the antenna characteristics on the network analyzer and verify the theoretical results with the practical ones.

  12. Level structures of 95,97Mo – A comparative study

    Indian Academy of Sciences (India)

    J M Chatterjee; M Saha Sarkar; S Bhattacharya; P Banerjee; S Sarkar; R P Singh; S Murulithar; R K Bhowmik

    2001-07-01

    High-spin states of 95,97Mo ( = 42, = 53, 55) nuclei have been investigated through 82Se(18O, ) reaction at = 60 MeV. The level scheme in 95Mo has been observed upto ≃ 10 MeV in the present experiment. The level structure shows mainly single particle character. In 97Mo, the ground state level sequence has been extended to ≃ 4.5 MeV while the previous information had been up to 2.4 MeV. A negative parity band built on 1437 keV (11/2-) excited state has been extended to 5.5 MeV. The structure seems to show a coexistence of single particle and collective modes of excitation. Properties of both the nuclei have been compared with shell model calculations using OXBASH.

  13. Anisotropic Mo2-phthalocyanine sheet: a new member of the organometallic family.

    Science.gov (United States)

    Zhu, Guizhi; Kan, Min; Sun, Qiang; Jena, Puru

    2014-01-09

    Metal-organic porous sheets, due to their unique atomic configurations and properties, represent a class of materials beyond graphene and BN monolayers. The Mo2-phthalocyanine-based sheet (Mo2Pc) is a new member of this porous organometallic family. Using density functional theory with hybrid functional for exchange-correlation potential, we show that this dimer-based material, unlike conventional organic monolayers that contain isolated metal atoms, possesses unique mechanical, magnetic, electronic, and optical properties due to inherent anisotropy in the structure. Furthermore, it is a semiconductor with a direct band gap of 0.93 eV and is antiferromagnetic with each Mo site carrying a magnetic moment of 0.88 μB. The strong anisotropy in elasticity and infrared light absorption is likely to open new doors for potential applications.

  14. Optical and luminescence studies of ZnMoO 4 using vacuum ultraviolet synchrotron radiation

    Science.gov (United States)

    Mikhailik, V. B.; Kraus, H.; Wahl, D.; Ehrenberg, H.; Mykhaylyk, M. S.

    2006-06-01

    In this paper we present a characterisation of ZnMoO 4 using spectroscopic techniques. Reflection, luminescence and luminescence excitation spectra were measured over the temperature range 8-295 K using VUV synchrotron radiation. The emission spectrum of the crystal exhibits a broad band with a maximum around 1.95 eV at 80 K that is attributed to the radiative transitions within MO 42- oxyanion complex. An interpretation of the observed features of the electronic excitations in the crystal is given based on present knowledge of the electronic structure and emission properties of molybdate crystals. The results of this study suggest that ZnMoO 4 is a suitable candidate for further testing for implementation as a target material in cryogenic scintillation searches for rare events.

  15. Optical and luminescence studies of ZnMoO{sub 4} using vacuum ultraviolet synchrotron radiation

    Energy Technology Data Exchange (ETDEWEB)

    Mikhailik, V.B. [Department of Physics, University of Oxford, Keble Road, Oxford OX1 3RH (United Kingdom)]. E-mail: vmikhai@hotmail.com; Kraus, H. [Department of Physics, University of Oxford, Keble Road, Oxford OX1 3RH (United Kingdom); Wahl, D. [Department of Physics, University of Oxford, Keble Road, Oxford OX1 3RH (United Kingdom); Ehrenberg, H. [Material Science, Darmstadt University of Technology, Petersenstr. 23, Darmstadt 64287 (Germany); Mykhaylyk, M.S. [Physics Department, Lviv National University, 8 Kyryla and Mefodiya str., Lviv, 79005 (Ukraine)

    2006-06-15

    In this paper we present a characterisation of ZnMoO{sub 4} using spectroscopic techniques. Reflection, luminescence and luminescence excitation spectra were measured over the temperature range 8-295 K using VUV synchrotron radiation. The emission spectrum of the crystal exhibits a broad band with a maximum around 1.95 eV at 80 K that is attributed to the radiative transitions within MO{sub 4} {sup 2-} oxyanion complex. An interpretation of the observed features of the electronic excitations in the crystal is given based on present knowledge of the electronic structure and emission properties of molybdate crystals. The results of this study suggest that ZnMoO{sub 4} is a suitable candidate for further testing for implementation as a target material in cryogenic scintillation searches for rare events.

  16. Defect assisted coupling of a MoS2/TiO2 interface and tuning of its electronic structure.

    Science.gov (United States)

    Chen, Guifeng; Song, Xiaolin; Guan, Lixiu; Chai, Jianwei; Zhang, Hui; Wang, Shijie; Pan, Jisheng; Tao, Junguang

    2016-09-01

    Although MoS2 based heterostructures have drawn increased attention, the van der Waals forces within MoS2 layers make it difficult for the layers to form strong chemical coupled interfaces with other materials. In this paper, we demonstrate the successful strong chemical attachment of MoS2 on TiO2 nanobelts after appropriate surface modifications. The etch-created dangling bonds on TiO2 surfaces facilitate the formation of a steady chemically bonded MoS2/TiO2 interface. With the aid of high resolution transmission electron microscope measurements, the in-plane structure registry of MoS2/TiO2 is unveiled at the atomic scale, which shows that MoS2[1-10] grows along the direction of TiO2[001] and MoS2[110] parallel to TiO2[100] with every six units of MoS2 superimposed on five units of TiO2. Electronically, type II band alignments are realized for all surface treatments. Moreover, the band offsets are delicately correlated to the surface states, which plays a significant role in their photocatalytic performance.

  17. Vibrational and optical properties of MoS2: From monolayer to bulk

    Science.gov (United States)

    Molina-Sánchez, Alejandro; Hummer, Kerstin; Wirtz, Ludger

    2015-12-01

    Molybdenum disulfide, MoS2, has recently gained considerable attention as a layered material where neighboring layers are only weakly interacting and can easily slide against each other. Therefore, mechanical exfoliation allows the fabrication of single and multi-layers and opens the possibility to generate atomically thin crystals with outstanding properties. In contrast to graphene, it has an optical gap of ~1.9 eV. This makes it a prominent candidate for transistor and opto-electronic applications. Single-layer MoS2 exhibits remarkably different physical properties compared to bulk MoS2 due to the absence of interlayer hybridization. For instance, while the band gap of bulk and multi-layer MoS2 is indirect, it becomes direct with decreasing number of layers. In this review, we analyze from a theoretical point of view the electronic, optical, and vibrational properties of single-layer, few-layer and bulk MoS2. In particular, we focus on the effects of spin-orbit interaction, number of layers, and applied tensile strain on the vibrational and optical properties. We examine the results obtained by different methodologies, mainly ab initio approaches. We also discuss which approximations are suitable for MoS2 and layered materials. The effect of external strain on the band gap of single-layer MoS2 and the crossover from indirect to direct band gap is investigated. We analyze the excitonic effects on the absorption spectra. The main features, such as the double peak at the absorption threshold and the high-energy exciton are presented. Furthermore, we report on the the phonon dispersion relations of single-layer, few-layer and bulk MoS2. Based on the latter, we explain the behavior of the Raman-active A1g and E2g1 modes as a function of the number of layers. Finally, we compare theoretical and experimental results of Raman, photoluminescence, and optical-absorption spectroscopy.

  18. Phase equilibria in the Mo-Fe-P system at 800 °C and structure of ternary phosphide (Mo(1-x)Fe(x))3P (0.10 ≤ x ≤ 0.15).

    Science.gov (United States)

    Oliynyk, Anton O; Lomnytska, Yaroslava F; Dzevenko, Mariya V; Stoyko, Stanislav S; Mar, Arthur

    2013-01-18

    Construction of the isothermal section in the metal-rich portion (<67 atom % P) of the Mo-Fe-P phase diagram at 800 °C has led to the identification of two new ternary phases: (Mo(1-x)Fe(x))(2)P (x = 0.30-0.82) and (Mo(1-x)Fe(x))(3)P (x = 0.10-0.15). The occurrence of a Co(2)Si-type ternary phase (Mo(1-x)Fe(x))(2)P, which straddles the equiatomic composition MoFeP, is common to other ternary transition-metal phosphide systems. However, the ternary phase (Mo(1-x)Fe(x))(3)P is unusual because it is distinct from the binary phase Mo(3)P, notwithstanding their similar compositions and structures. The relationship has been clarified through single-crystal X-ray diffraction studies on Mo(3)P (α-V(3)S-type, space group I42m, a = 9.7925(11) Å, c = 4.8246(6) Å) and (Mo(0.85)Fe(0.15))(3)P (Ni(3)P-type, space group I4, a = 9.6982(8) Å, c = 4.7590(4) Å) at -100 °C. Representation in terms of nets containing fused triangles provides a pathway to transform these closely related structures through twisting. Band structure calculations support the adoption of these structure types and the site preference of Fe atoms. Electrical resistivity measurements on (Mo(0.85)Fe(0.15))(3)P reveal metallic behavior but no superconducting transition.

  19. The influence of MoOx gap states on hole injection from aluminum doped zinc oxide with nanoscale MoOx surface layer anodes for organic light emitting diodes

    Science.gov (United States)

    Jha, Jitendra Kumar; Santos-Ortiz, Reinaldo; Du, Jincheng; Shepherd, Nigel D.

    2015-08-01

    The effective workfunction of Al doped ZnO films (AZO) increased from 4.1 eV to 5.55 eV after surface modification with nanoscale molybdenum sub-oxides (MoOx). Hole only devices with anodes consisting of 3 nm of MoOx on AZO exhibited a lower turn-on voltage (1.5 vs 1.8 V), and larger charge injection (190 vs 118 mA/cm2) at the reference voltage, compared to indium tin oxide (ITO). AZO devices with 10 nm of MoOx exhibited the highest workfunction but performed poorly compared to devices with 3 nm of MoOx, or standard ITO. Ultraviolet photoelectron, X-ray photoelectron, and optical spectroscopies indicate that the 3 nm MoOx films are more reduced and farther away from MoO3 stoichiometry than their 10 nm equivalents. The vacancies associated with non-stoichiometry result in donor-like gap states which we assign to partially occupied Mo 4d levels. We propose that Fowler-Nordheim tunneling from these levels is responsible for the reduction in threshold voltage measured in devices with 3 nm of MoOx. A schematic band diagram is proposed. The thicker MoOx layers are more stoichiometric and resistive, and the voltage drop across these layers dominates their electrical performance, leading to an increase in threshold voltage. The results indicate that AZO with MoOx layers of optimal thickness may be potential candidates for anode use in organic light emitting diodes.

  20. Fermi arc electronic structure and Chern numbers in the type-II Weyl semimetal candidate MoxW1<mo>-mo>xTe2

    Energy Technology Data Exchange (ETDEWEB)

    Belopolski, Ilya; Xu, Su-Yang; Ishida, Yukiaki; Pan, Xingchen; Yu, Peng; Sanchez, Daniel S.; Zheng, Hao; Neupane, Madhab; Alidoust, Nasser; Chang, Guoqing; Chang, Tay-Rong; Wu, Yun; Bian, Guang; Huang, Shin-Ming; Lee, Chi-Cheng; Mou, Daixiang; Huang, Lunan; Song, You; Wang, Baigeng; Wang, Guanghou; Yeh, Yao-Wen; Yao, Nan; Rault, Julien E.; Le Fèvre, Patrick; Bertran, François; Jeng, Horng-Tay; Kondo, Takeshi; Kaminski, Adam; Lin, Hsin; Liu, Zheng; Song, Fengqi; Shin, Shik; Hasan, M. Zahid

    2016-08-15

    It has recently been proposed that electronic band structures in crystals can give rise to a previously overlooked type of Weyl fermion, which violates Lorentz invariance and, consequently, is forbidden in particle physics. It was further predicted that Mo x W 1 - x Te 2 may realize such a type-II Weyl fermion. Here, we first show theoretically that it is crucial to access the band structure above the Fermi level ε F to show a Weyl semimetal in Mo x W 1 - x Te 2 . Then, we study Mo x W 1 - x Te 2 by pump-probe ARPES and we directly access the band structure > 0.2 eV above ε F in experiment. By comparing our results with ab initio calculations, we conclude that we directly observe the surface state containing the topological Fermi arc. We propose that a future study of Mo x W 1 - x Te 2 by pump-probe ARPES may directly pinpoint the Fermi arc. Our work sets the stage for the experimental discovery of the first type-II Weyl semimetal in Mo x W 1 - x Te 2 .

  1. Dynamic Structure of Mo-O Species in Ag-Mo-P-O Catalyst for Oxidative Dehydrogenation of Propane

    Institute of Scientific and Technical Information of China (English)

    2002-01-01

    The dynamic structure of Mo-O species in Ag-Mo-P-O catalyst was studied by in situ confocal microprobe laser Raman spectroscopy (LRS) and catalytic test. The results indicate Mo-O species of MoO3 transformed to Mo-O species of AgMoO2PO4 in C3H8/O2/N2 (3/1/4) flow at 773 K. This behavior is closely relative to oxidative dehydrogenation of propane and intrinsic properties of Mo-O species. The Mo-O species of AgMoO2PO4 may be active species for oxidative dehydrogenation of propane.

  2. Structural instability and ground state of the U{sub 2}Mo compound

    Energy Technology Data Exchange (ETDEWEB)

    Losada, E.L., E-mail: losada@cab.cnea.gov.ar [SIM" 3, Centro Atómico Bariloche, Comisión Nacional de Energía Atómica (Argentina); Garcés, J.E. [Gerencia de Investigación y Aplicaciones Nucleares, Comisión Nacional de Energía Atómica (Argentina)

    2015-11-15

    This work reports on the structural instability at T = 0 °K of the U{sub 2}Mo compound in the C11{sub b} structure under the distortion related to the C{sub 66} elastic constant. The electronic properties of U{sub 2}Mo such as density of states (DOS), bands and Fermi surface (FS) are studied to understand the source of the instability. The C11{sub b} structure can be interpreted as formed by parallel linear chains along the z-directions each one composed of successive U–Mo–U blocks. Hybridization due to electronic interactions inside the U–Mo–U blocks is slightly modified under the D{sub 6} distortion. The change in distance between chains modifies the U–U interaction and produces a split of f-states. The distorted structure is stabilized by a decrease in energy of the hybridized states, mainly between d-Mo and f-U states, together with the f-band split. Consequently, an induced Peierls distortion is produced in U{sub 2}Mo due to the D{sub 6} distortion. It is important to note that the results of this work indicate that the structure of the ground state of the U{sub 2}Mo compound is not the assumed C11{sub b} structure. It is suggested for the ground state a structure with hexagonal symmetry (P6 #168), ∼0.1 mRy below the energy of the recently proposed Pmmn structure. - Highlights: • Structural instability of the C11b compound due to the D6 deformation. • Induced Peierls distortion due to the D6 deformation. • Distorted structure is stabilized by hybridization and split of f-Uranium state. • P6 (#168) suggested ground state for the U{sub 2}Mo compound.

  3. Synthesis, surface structure and optical properties of double perovskite Sr2NiMoO6 nanoparticles

    Science.gov (United States)

    Xu, Lei; Wan, Yingpeng; Xie, Hongde; Huang, Yanlin; Yang, Li; Qin, Lin; Seo, Hyo Jin

    2016-12-01

    Double perovskite Sr2NiMoO6 nanoparticles were synthesized via the chemical sol-gel route. The phase formation was investigated through X-ray polycrystalline diffraction (XRD) and Rietveld refinements. The perovskite crystallized in worm-like nano-grains with the diameter of 20-50 nm. The optical properties were measured by the optical absorption spectra. The nanoparticles present an indirect allowed transition with a narrow band gap of 2.1 eV. Sr2NiMoO6 nanoparticles have obvious photocatalytic ability on the degradation of Rhodamine B (RhB) solutions under the irradiation of visible light. The transport behaviors of the excitons were investigated from the photoluminescence spectra and the corresponding decay lifetimes. Sr2NiMoO6 nanoparticles present several advantages for photocatalysis such as the appropriate band energy positions, the quenched luminescence, and the coexistence of multivalent ions in the lattices.

  4. Field-Induced Superconductivity in MoS2 (Retracted article. See vol. 27, pg. 2645, 2014)

    NARCIS (Netherlands)

    Ye, J. T.; Zhang, Y. J.; Yoshida, M.; Saito, Y.; Iwasa, Y.

    Semiconducting TMDs are nowadays attracting great interest after the invention of the so-called "Scotch-tape method" established in graphene research. Semiconducting TMDs are front-runners of "post graphene" materials for their finite band gap crucial for device applications. MoS2 is the most widely

  5. Field-Induced Superconductivity in MoS2 (Retracted article. See vol. 27, pg. 2645, 2014)

    NARCIS (Netherlands)

    Ye, J. T.; Zhang, Y. J.; Yoshida, M.; Saito, Y.; Iwasa, Y.

    2014-01-01

    Semiconducting TMDs are nowadays attracting great interest after the invention of the so-called "Scotch-tape method" established in graphene research. Semiconducting TMDs are front-runners of "post graphene" materials for their finite band gap crucial for device applications. MoS2 is the most widely

  6. Reduction of Fermi level pinning at Au-MoS2 interfaces by atomic passivation on Au surface

    Science.gov (United States)

    Min, Kyung-Ah; Park, Jinwoo; Wallace, Robert M.; Cho, Kyeongjae; Hong, Suklyun

    2017-03-01

    Monolayer molybdenum disulfide (MoS2), which is a semiconducting material with direct band gap of ˜1.8 eV, has drawn much attention for application in field effect transistors (FETs). In this connection, it is very important to understand the Fermi level pinning (FLP) which occurs at metal-semiconductor interfaces. It is known that MoS2 has an n-type contact with Au, which is a high work function metal, representing the strong FLP at Au-MoS2 interfaces. However, such FLP can obstruct the attainment of high performance of field effect devices. In this study, we investigate the reduction of FLP at Au-MoS2 interfaces by atomic passivation on Au(111) using first-principles calculations. To reduce the FLP at Au-MoS2 interfaces, we consider sulfur, oxygen, nitrogen, fluorine, and hydrogen atoms that can passivate the surface of Au(111). Calculations show that passivating atoms prevent the direct contact between Au(111) and MoS2, and thus FLP at Au-MoS2 interfaces is reduced by weak interaction between atom-passivated Au(111) and MoS2. Especially, FLP is greatly reduced at sulfur-passivated Au-MoS2 interfaces with the smallest binding energy. Furthermore, fluorine-passivated Au(111) can form ohmic contact with MoS2, representing almost zero Schottky barrier height (SBH). We suggest that SBH can be controlled depending on the passivating atoms on Au(111).

  7. In Situ FT-IR Spectroscopic Studies of CO Adsorption on Fresh Mo2C/Al2O3 Catalyst.

    Science.gov (United States)

    Wu, Weicheng; Wu, Zili; Liang, Changhai; Chen, Xiaowei; Ying, Pinliang; Li, Can

    2003-07-24

    The surface sites of supported molybdenum carbide catalyst derived from different synthesis stages have been studied by in situ FT-IR spectroscopy using CO as the probe molecule. Adsorbed CO on the reduced passivated Mo2C/Al2O3 catalyst gives a main band at 2180 cm(-1), which can be assigned to linearly adsorbed CO on Mo(4+) sites. The IR results show that the surface of reduced passivated sample is dominated by molybdenum oxycarbide. However, a characteristic IR band at 2054 cm(-1) was observed for the adsorbed CO on MoO3/Al2O3 carburized with CH4/H2 mixture at 1033 K (fresh Mo2C/Al2O3), which can be assigned to linearly adsorbed CO on Mo(δ+) (0 Mo2C/Al2O3. Unlike adsorbed CO on reduced passivated Mo2C/Al2O3 catalyst, the IR spectra of adsorbed CO on fresh Mo2C/Al2O3 shows similarity to that on some of the group VIII metals (such as Pt and Pd), suggesting that fresh carbide resembles noble metals. To study the stability of Mo2C catalyst during H2 treatment and find proper conditions to remove the deposited carbon species, H2 treatment of fresh Mo2C/Al2O3 catalyst at different temperatures was conducted. Partial amounts of carbon atoms in Mo2C along with some surface-deposited carbon species can be removed by the H2 treatment even at 450 K. Both the surface-deposited carbon species and carbon atoms in carbide can be extensively removed at temperatures above 873 K.

  8. Photoluminescence Enhancement and Structure Repairing of Monolayer MoSe 2 by Hydrohalic Acid Treatment

    KAUST Repository

    Han, Hau-Vei

    2015-12-30

    Atomically thin two-dimensional transition-metal dichalcogenides (TMDCs) have attracted much attention recently due to their unique electronic and optical properties for future optoelectronic devices. The chemical vapor deposition (CVD) method is able to generate TMDCs layers with a scalable size and a controllable thickness. However, the TMDC monolayers grown by CVD may incorporate structural defects, and it is fundamentally important to understand the relation between photoluminescence and structural defects. In this report, point defects (Se vacancies) and oxidized Se defects in CVD-grown MoSe2 monolayers are identified by transmission electron microscopy and X-ray photoelectron spectroscopy. These defects can significantly trap free charge carriers and localize excitons, leading to the smearing of free band-to-band exciton emission. Here, we report that the simple hydrohalic acid treatment (such as HBr) is able to efficiently suppress the trap-state emission and promote the neutral exciton and trion emission in defective MoSe2 monolayers through the p-doping process, where the overall photoluminescence intensity at room temperature can be enhanced by a factor of 30. We show that HBr treatment is able to activate distinctive trion and free exciton emissions even from highly defective MoSe2 layers. Our results suggest that the HBr treatment not only reduces the n-doping in MoSe2 but also reduces the structural defects. The results provide further insights of the control and tailoring the exciton emission from CVD-grown monolayer TMDCs.

  9. Photoemission study on the formation of Mo contacts to CuInSe sub 2

    Energy Technology Data Exchange (ETDEWEB)

    Nelson, A.J.; Niles, D.W.; Kazmerski, L.L. (National Renewable Energy Laboratory, Golden, Colorado 80401 (United States)); Rioux, D.; Patel, R.; Hoechst, H. (Synchrotron Radiation Center, University of Wisconsin-Madison, 3731 Schneider Drive, Stoughton, Wisconsin 53589 (United States))

    1992-08-01

    Synchrotron radiation soft-x-ray photoemission spectroscopy was used to investigate the development of the electronic structure at the Mo/CuInSe{sub 2} interface. Mo overlayers were {ital e}-beam deposited in steps on single-crystal {ital n}-type CuInSe{sub 2} at ambient temperature. Photoemission measurements were acquired after each growth in order to observe changes in the valence-band electronic structure as well as changes in the In 4{ital d}, Se 3{ital d}, and Mo 4{ital d} core lines. Photoemission measurements on the valence-band and core lines were also obtained after annealing. The results were used to correlate the interface chemistry with the electronic structure at this interface and to directly determine the maximum possible Schottky barrier height {phi}{sub {ital b}} to be {le}0.2 eV at the Mo/CuInSe{sub 2} junction before annealing, thus showing that this contact is essentially ohmic.

  10. Photoluminescence Enhancement and Structure Repairing of Monolayer MoSe2 by Hydrohalic Acid Treatment.

    Science.gov (United States)

    Han, Hau-Vei; Lu, Ang-Yu; Lu, Li-Syuan; Huang, Jing-Kai; Li, Henan; Hsu, Chang-Lung; Lin, Yung-Chang; Chiu, Ming-Hui; Suenaga, Kazu; Chu, Chih-Wei; Kuo, Hao-Chung; Chang, Wen-Hao; Li, Lain-Jong; Shi, Yumeng

    2016-01-26

    Atomically thin two-dimensional transition-metal dichalcogenides (TMDCs) have attracted much attention recently due to their unique electronic and optical properties for future optoelectronic devices. The chemical vapor deposition (CVD) method is able to generate TMDCs layers with a scalable size and a controllable thickness. However, the TMDC monolayers grown by CVD may incorporate structural defects, and it is fundamentally important to understand the relation between photoluminescence and structural defects. In this report, point defects (Se vacancies) and oxidized Se defects in CVD-grown MoSe2 monolayers are identified by transmission electron microscopy and X-ray photoelectron spectroscopy. These defects can significantly trap free charge carriers and localize excitons, leading to the smearing of free band-to-band exciton emission. Here, we report that the simple hydrohalic acid treatment (such as HBr) is able to efficiently suppress the trap-state emission and promote the neutral exciton and trion emission in defective MoSe2 monolayers through the p-doping process, where the overall photoluminescence intensity at room temperature can be enhanced by a factor of 30. We show that HBr treatment is able to activate distinctive trion and free exciton emissions even from highly defective MoSe2 layers. Our results suggest that the HBr treatment not only reduces the n-doping in MoSe2 but also reduces the structural defects. The results provide further insights of the control and tailoring the exciton emission from CVD-grown monolayer TMDCs.

  11. MoS2 nanocrystals confined in a DNA matrix exhibiting energy transfer.

    Science.gov (United States)

    Goswami, Nirmal; Giri, Anupam; Pal, Samir Kumar

    2013-09-10

    We report the wet chemical synthesis of MoS2 nanocrystals (NCs), a transition-metal dichalcogenide, using DNA as a host matrix. As evidenced from transmission electron microscopy (TEM), the NCs are highly crystalline, with an average diameter of ~5 nm. Ultraviolet-visible (UV-vis) absorption studies along with band gap calculations confirm that NCs are in quantum confinement. A prominent red shift of the optical absorption bands has been observed upon formation of the thin film using hexadecyltrimethylammonium chloride (CTAC), i.e., in the case of MoS2@DNA-CTAC. In the thin film, strong electron-phonon coupling arises because of the resonance effect, which is reflected from the emergence of intense first-, second-, and third-order Raman peaks, whenever excited with the 488 nm line. We have established that our as-synthesized MoS2 NCs quench the fluorescence of a well-known DNA minor groove binding probe, Hoechst 33258. Unprecedented fluorescence quenching (94%) of donor (Hoechst 33258) emission and efficient energy transfer (89%) between Hoechst 33258 and MoS2 NCs (acceptor) are obtained. The donor-acceptor distance of these conjugates has been described by a Förster resonance energy transfer (FRET)-based model. Furthermore, employing a statistical method, we have estimated the probability of the distance distribution between the donor and acceptor. We believe that the study described herein may enable substantial advances in fields of optoelectronics, photovoltaics, catalysis, and many others.

  12. Tuning the optical emission of MoS{sub 2} nanosheets using proximal photoswitchable azobenzene molecules

    Energy Technology Data Exchange (ETDEWEB)

    Li, Juan [Physik Department and NIM, Walter Schottky Institute, Technische Universität München, Am Coulombwall 4, Garching D-85748 (Germany); Physik Department E20, Technische Universität München, James-Franck-St. 1, Garching D-85748 (Germany); Wierzbowski, Jakob; Ceylan, Özlem; Klein, Julian; Anh, Tuan Le; Meggendorfer, Felix; Finley, Jonathan J.; Margapoti, Emanuela, E-mail: emanuela.margapoti@wsi.tum.de [Physik Department and NIM, Walter Schottky Institute, Technische Universität München, Am Coulombwall 4, Garching D-85748 (Germany); Nisic, Filippo; Dragonetti, Claudia [Dipartimento di Chimica, Università degli Studi di Milano and UdR dell' INSTM di Milano, Via Golgi 19, I-20133 Milano (Italy); Palma, Carlos-Andres; Barth, Johannes V. [Physik Department E20, Technische Universität München, James-Franck-St. 1, Garching D-85748 (Germany)

    2014-12-15

    We report photoluminescence measurements performed on monolayer- and two-layer-MoS{sub 2} placed on two types of mixed self-assembled monolayers (mSAMs) of photoswitchable azobenzene molecules. The two mSAMs differ via the electronegative character of the azobenzene derivatives. Thin layers of a transition metal dichalcogenide—MoS{sub 2}—were mechanically exfoliated on mSAM to allow for direct interaction between the molecules and the MoS{sub 2} layers. When the MoS{sub 2} nanosheet is in contact with the electropositive azobenzene molecules in trans configuration, an emission side band at lower energies and at low excitation powers suggest n-type doping. The photoisomerization of the molecules from trans to cis configuration lowers the doping, quenching the side band and enhancing the overall PL efficiency by a factor of ∼3. Opposite results were observed with the chlorinated, more electronegative molecules, exhibiting a reversed trend in the PL efficiency between trans and cis, but with an overall larger intensity. The type of doping induced by the two types of mSAMs was determined by Kelvin probe force microscopy technique.

  13. Synthesis and spectroscopic properties of multiferroic β‧-Tb2(MoO4)3

    Science.gov (United States)

    Atuchin, V. V.; Aleksandrovsky, A. S.; Chimitova, O. D.; Krylov, A. S.; Molokeev, M. S.; Bazarov, B. G.; Bazarova, J. G.; Xia, Zhiguo

    2014-08-01

    Orthorhombic terbium molybdate, β‧-Tb2(MoO4)3, microcrystals have been fabricated by solid state synthesis at T = 750-1270 K for t = 290 h. The crystal structure β‧-Tb2(MoO4)3 has been refined by Rietveld method in space group Pba2 with cell parameters of a = 10.35387(6), b = 10.38413(6) and c = 10.65695(7) Å (RB = 1.83%). About 40 narrow Raman lines have been observed in the Raman spectrum recorded for the β‧-Tb2(MoO4)3 powder sample. The luminescence spectrum of β‧-Tb2(MoO4)3 has been measured under the excitation at 355 nm, and the intensive photoluminescence band at 540-550 nm has been found.

  14. Characterization of the second- and third-order nonlinear optical susceptibilities of monolayer MoS$_2$ using multiphoton microscopy

    CERN Document Server

    Woodward, R I; Phelan, C F; de Oliveira, R E P; Runcorn, T H; Kelleher, E J R; Li, S; de Oliveira, E C; Fechine, G J M; Eda, G; de Matos, C J S

    2016-01-01

    We report second- and third-harmonic generation in monolayer MoS$_2$ as a tool for imaging and accurately characterizing the material's nonlinear optical properties under 1560 nm excitation. Using a surface nonlinear optics treatment, we derive expressions relating experimental measurements to second- and third-order nonlinear sheet susceptibility magnitudes, obtaining values of $|\\chi_s^{(2)}|=2\\times10^{-20}$ m$^2$ V$^{-1}$ and for the first time for monolayer MoS$_2$, $|\\chi_s^{(3)}|=2\\times10^{-28}$ m$^3$ V$^{-2}$. Experimental comparisons between MoS$_2$ and graphene are also performed, demonstrating $\\sim$4 times stronger third-order nonlinearity in monolayer MoS$_2$, highlighting the material's potential for nonlinear photonics in the telecommunications C band.

  15. Recent Advancement on the Optical Properties of Two-Dimensional Molybdenum Disulfide (MoS2 Thin Films

    Directory of Open Access Journals (Sweden)

    Mingxiao Ye

    2015-03-01

    Full Text Available The emergence of two-dimensional (2D materials has led to tremendous interest in the study of graphene and a series of mono- and few-layered transition metal dichalcogenides (TMDCs. Among these TMDCs, the study of molybdenum disulfide (MoS2 has gained increasing attention due to its promising optical, electronic, and optoelectronic properties. Of particular interest is the indirect to direct band-gap transition from bulk and few-layered structures to mono-layered MoS2, respectively. In this review, the study of these properties is summarized. The use of Raman and Photoluminescence (PL spectroscopy of MoS2 has become a reliable technique for differentiating the number of molecular layers in 2D MoS2.

  16. Two photon absorption and its saturation of WS2 and MoS2 monolayer and few-layer films

    CERN Document Server

    Zhang, Saifeng; McEvoy, Niall; O'Brien, Maria; Winters, Sinéad; Berner, Nina C; Yim, Chanyoung; Zhang, Xiaoyan; Chen, Zhanghai; Zhang, Long; Duesberg, Georg S; Wang, Jun

    2015-01-01

    The optical nonlinearity of WS2, MoS2 monolayer and few-layer films was investigated using the Z-scan technique with femtosecond pulses from the visible to the near infrared. The dependence of nonlinear absorption of the WS2 and MoS2 films on layer number and excitation wavelength was studied systematically. WS2 with 1~3 layers exhibits a giant two-photon absorption (TPA) coefficient. Saturation of TPA for WS2 with 1~3 layers and MoS2 with 25~27 layers was observed. The giant nonlinearity of WS2 and MoS2 is attributed to two dimensional confinement, a giant exciton effect and the band edge resonance of TPA.

  17. Van der Waals epitaxial growth of MoS2 on SiO2/Si by chemical vapor deposition

    KAUST Repository

    Cheng, Yingchun

    2013-01-01

    Recently, single layer MoS2 with a direct band gap of 1.9 eV has been proposed as a candidate for two dimensional nanoelectronic devices. However, the synthetic approach to obtain high-quality MoS2 atomic thin layers is still problematic. Spectroscopic and microscopic results reveal that both single layers and tetrahedral clusters of MoS2 are deposited directly on the SiO2/Si substrate by chemical vapor deposition. The tetrahedral clusters are mixtures of 2H- and 3R-MoS2. By ex situ optical analysis, both the single layers and tetrahedral clusters can be attributed to van der Waals epitaxial growth. Due to the similar layered structures we expect the same growth mechanism for other transition-metal disulfides by chemical vapor deposition. © 2013 The Royal Society of Chemistry.

  18. Two-dimensional MoTe2 materials: From synthesis, identification, and charge transport to electronics applications

    Science.gov (United States)

    Chang, Yuan-Ming; Lin, Che-Yi; Lin, Yen-Fu; Tsukagoshi, Kazuhito

    2016-11-01

    We present a review of recent developments in the synthesis, thickness identification, electronic properties, and possible applications of layered MoTe2 flakes. Special emphasis is made on two-dimensional (2D) MoTe2 semiconductors and the extensive research in recent years on their applications in electronics. Layered MoTe2 flakes have been the focus of substantial interest in the research community because of their fascinating characteristics, including an appropriate band gap and a simple fabrication method (exfoliation) to form layered nanomaterials. Our aim is to provide the readers an overview of layered MoTe2 flakes and to understand their properties, which may lead to their applications in micro- and nanoelectronics.

  19. Giant valley drifts in uniaxially strained monolayer MoS2

    KAUST Repository

    Zhang, Qingyun

    2013-12-30

    Using first-principles calculations, we study the electronic structure of monolayer MoS2 under uniaxial strain. We show that the energy valleys drift far off the corners of the Brillouin zone (K points), about 12 times the amount observed in graphene. Therefore, it is essential to take this effect into consideration for a correct identification of the band gap. The system remains a direct band gap semiconductor up to 4% uniaxial strain, while the size of the band gap decreases from 1.73 to 1.54 eV. We also demonstrate that the splitting of the valence bands due to inversion symmetry breaking and spin-orbit coupling is not sensitive to strain.

  20. First principles study on molecule doping in MoS2 monolayer%单层MoS2分子掺杂的第一性原理研究

    Institute of Scientific and Technical Information of China (English)

    刘俊; 梁培; 舒海波; 沈涛; 邢凇; 吴琼

    2014-01-01

    基于密度泛函理论的第一性原理平面波赝势方法的计算,研究了通过吸附不同有机分子对单层MoS2进行化学掺杂。计算结果表明有机分子与MoS2单层衬底间的相互作用主要是范德瓦尔斯作用力。吸附不同有机分子的单层MoS2结构均表现出间接带隙的特征,还表明吸附TTF分子的单层MoS2结构表现出n型半导体的特质,而吸附TCNQ, TCNE两种分子的单层MoS2结构均表现出p型半导体的性质,这些结果表明可以通过改变吸附的分子来实现对单层MoS2的掺杂类型的调控。本文的研究结果将对单层MoS2在晶体管中的应用提供理论基础和指导。%The chemical doping of organic molecules adsorbed on MoS2 monolayers are systematically studied by using plane-wave pseudo-potential method based on the density functional theory. Our results indicate that the interaction between organic molecules and the MoS2 monolayer substrate is of van der Waals’ type of force. Structure of monolayer MoS2 which adsorbs different organic molecules, exhibits indirect bandgap characteristics, and the energy band structure of monolayer MoS2 which adsorbs TTF molecules exhibits n-type conducting characteristics. However, the structures of monolayer MoS2 which adsorbs TCNQ or TCNE molecules would exhibit p-type conductivity characteristics. Thus, the results indicate that the doping type of molecules in monolayer MoS2 can be regulated by adsorbing different molecules. Results of this study may provide a theoretical basis for single-layer MoS2 transistor and guidance for it in the application.

  1. Development of fission Mo-99 production technology

    Energy Technology Data Exchange (ETDEWEB)

    Park, Jin Ho; Choung, W. M.; Lee, K. I. and others

    2000-05-01

    Fission Mo-99 is the only parent nuclide of Tc-99m, an extremely useful tool for mdeical diagnosis, with an estimated usage of greater than 80% of nuclear medicine applicatons. HEU and LEU targets to optimize in HANARO irradiation condition suggested and designed for domestic production of fission Mo-99. The optimum process conditions are established in each unit process to meet quality requirements of fission Mo-99 products, and the results of performance test in combined process show Mo separation and purification yield of the above 97%. The concept of Tc generator production process is established, and the result of performance test show Tc production yield of 98.4% in Tc generator procuction process. The drafts is prepared for cooperation of technical cooperation and business investment with foreign country. Evaluation on economic feasibility is accompanied for fission Mo-99 and Tc-99m generator production.

  2. Diffuse interstellar absorption bands

    Institute of Scientific and Technical Information of China (English)

    XIANG FuYuan; LIANG ShunLin; LI AiGen

    2009-01-01

    The diffuse interstellar bands (DIBs) are a large number of absorption bands that are superposed on the interstellar extinction curve and are of interstellar origin. Since the discovery of the first two DIBs in the 1920s, the exact nature of DIBs still remains unclear. This article reviews the history of the detec-tions of DIBs in the Milky Way and external galaxies, the major observational characteristics of DIBs, the correlations or anti-correlations among DIBs or between DIBs and other interstellar features (e.g. the prominent 2175 Angstrom extinction bump and the far-ultraviolet extinction rise), and the proposed candidate carriers. Whether they are also present in circumstellar environments is also discussed.

  3. Diffuse interstellar absorption bands

    Institute of Scientific and Technical Information of China (English)

    2009-01-01

    The diffuse interstellar bands(DIBs) are a large number of absorption bands that are superposed on the interstellar extinction curve and are of interstellar origin. Since the discovery of the first two DIBs in the 1920s,the exact nature of DIBs still remains unclear. This article reviews the history of the detections of DIBs in the Milky Way and external galaxies,the major observational characteristics of DIBs,the correlations or anti-correlations among DIBs or between DIBs and other interstellar features(e.g. the prominent 2175 Angstrom extinction bump and the far-ultraviolet extinction rise),and the proposed candidate carriers. Whether they are also present in circumstellar environments is also discussed.

  4. Solution chemistry of Mo(III) and Mo(IV): Thermodynamic foundation for modeling localized corrosion

    Energy Technology Data Exchange (ETDEWEB)

    Wang Peiming [OLI Systems Inc., 108 American Road, Morris Plains, NJ 07950 (United States); Wilson, Leslie L.; Wesolowski, David J.; Rosenqvist, Joergen [Chemical Sciences Division, Oak Ridge National Laboratory, 1 Bethel Valley Road, Oak Ridge, TN 37831-6110 (United States); Anderko, Andrzej [OLI Systems Inc., 108 American Road, Morris Plains, NJ 07950 (United States)], E-mail: aanderko@olisystems.com

    2010-05-15

    To investigate the behavior of molybdenum dissolution products in systems that approximate localized corrosion environments, solubility of Mo(III) in equilibrium with solid MoO{sub 2} has been determined at 80 deg. C as a function of solution acidity, chloride concentration and partial pressure of hydrogen. The measurements indicate a strong increase in solubility with acidity and chloride concentration and a weak effect of hydrogen partial pressure. The obtained results have been combined with literature data for systems containing Mo(III), Mo(IV), and Mo(VI) in solutions to develop a comprehensive thermodynamic model of aqueous molybdenum chemistry. The model is based on a previously developed framework for simulating the properties of electrolyte systems ranging from infinite dilution to solid saturation or fused salt limit. To reproduce the measurements, the model assumes the presence of a chloride complex of Mo(III) (i.e., MoCl{sup 2+}) and hydrolyzed species (MoOH{sup 2+}, Mo(OH){sub 2}{sup +}, and Mo(OH){sub 3}{sup 0}) in addition to the Mo{sup 3+} ion. The model generally reproduces the experimental data within experimental scattering and provides a tool for predicting the phase behavior and speciation in complex, concentrated aqueous solutions. Thus, it provides a foundation for simulating the behavior of molybdenum species in localized corrosion environments.

  5. Synthesis, characterization and structural control of nano crystalline molybdenum oxide MoO{sub 3} single phase by low cost technique

    Energy Technology Data Exchange (ETDEWEB)

    Afify, H.H.; Hassan, S.A. [Solid State Department, Physics Division, National Research Centre, 33 El Bohouthst. (fromer El Tahrirst.), Dokki, P.O. 12622, Giza (Egypt); Abouelsayed, A., E-mail: as.abouelsayed@gmail.com [Spectroscopy Department, Physics Division, National Research Centre, 33 El Bohouthst. (fromer El Tahrirst.), Dokki, P.O. 12622, Giza (Egypt); Demian, S.E. [Solid State Department, Physics Division, National Research Centre, 33 El Bohouthst. (fromer El Tahrirst.), Dokki, P.O. 12622, Giza (Egypt); Zayed, H.A. [Physics Department, Faculty of Girls for Art, Sciences and Education, Ain Shams University (Egypt)

    2016-06-15

    Thermodynamically stable α- MoO{sub 3} thin film is prepared without any other phases of the molybdenum oxides. Simple and low coast spray pyrolysis technique is used. Growth conditions are optimized to produce pure α- MoO{sub 3} with controlled crystallite size and surface morphology. Small angle (GAXRD) diffractometer is used to elucidate the structure. Profile shape function (PSF) model is made for the experimental data. WinFit software is going first to fit (PSF) to use the refined profile parameters for determination of crystallite size and internal residual strain. The (GAXRD) patterns prove the existence of α- MoO{sub 3} only with layered structure, indicated by the appearance of only (0k0). The calculated crystallite sizes and the strain are found to range from 10 to 28 nm and 0.28%–0.05% respectively. Ultraviolet and Visible transmission measurements were performed over a wavelength range 190–2500 nm on the MoO{sub 3} thin films synthesized by spray pyrolysis technique at different substrate temperature. The two sub-bands corresponds to the electronic transition between the molybdenum oxidation states Mo{sup 4+}, Mo{sup 5+} and Mo{sup 6+} are observed. Quantitative information on the temperature-induced blue shift of the sub-bands was obtained by fitting the spectra with Lorentz functions. The transition from Mo{sup 5+} to Mo{sup 6+} oxidation states show a blue shift up to Tc = 325 °C. Above Tc, the transition Mo{sup 5+} to Mo{sup 6+} increases more drastically, resulting in an anomaly in the temperature-induced shift at Tc. The anomaly can be attributed to the amorphous-to-crystalline phase transition at 325 °C. In addition, both refractive index and extinction coefficient are calculated as a function of substrate temperature. - Highlights: • Single phase α-MoO{sub 3} nano crystalline MoO{sub 3} thin films have been synthesized. • Amorphous-to-crystalline phase transition occurs at 325 °C for MoO{sub 3} thin films. • A clear

  6. Large Area Single Crystal (0001) Oriented MoS2 Thin Films

    OpenAIRE

    Laskar, Masihhur R.; Ma, Lu; K, ShanthaKumar; Park, Pil Sung; Krishnamoorthy, Sriram; Nath, Digbijoy N.; Lu, Wu; Wu, Yiying; Rajan, Siddharth

    2013-01-01

    Layered metal dichalcogenide materials are a family of semiconductors with a wide range of energy band gaps and properties, and potential to open up new areas of physics and technology applications. However, obtaining high crystal quality thin films over a large area remains a challenge. Here we show that chemical vapor deposition (CVD) can be used to achieve large area electronic grade single crystal Molybdenum Disulfide (MoS2) thin films with the highest mobility reported in CVD grown films...

  7. Effects of Mo on the Microstructure and Hydrogen Sorption Properties of Ti-Mo Getters

    Institute of Scientific and Technical Information of China (English)

    ZHOU Hong-guo; WEI Xiu-ying; MAO Chang-hui; XIONG Yu-hua; QIN Guang-rong

    2007-01-01

    The effects of Mo on the microstructure evolution, porosity and hydrogen sorption properties of Ti-Mo getters are investigated in this work. The results show that the addition of Mo prolongs the densification process of Ti-Mo getters and results in a significant amount of sintered pores. With the Mo content increasing, the porosity of getters firstly increases reaching the maximum value as it attains about 7.5wt.%, and then drops. At the room temperature, the hydrogen sorption property of getters increases progressively with the Mo content increasing, but the tendency is not very clear before its content lies below 2.5wt.%. When the Mo content achieves about7.5wt.%, the hydrogen sorption property proves to be the best. The discussion is made about the above mentioned phenomena inclusive of hydrogen sorption properties of getters under different activation conditions (from 500-750 ℃).

  8. Enhancement of band-to-band tunneling in mono-layer transition metal dichalcogenides two-dimensional materials by vacancy defects

    Energy Technology Data Exchange (ETDEWEB)

    Jiang, Xiang-Wei; Li, Shu-Shen [State Key Laboratory of Superlattices and Microstructures, Institute of Semiconductors, Chinese Academy of Sciences, Beijing 100083 (China); Gong, Jian [School of Physics Science and Technology, Inner Mongolia University, Hohhot 010021 (China); Xu, Nuo [Department of Electrical Engineering and Computer Sciences, University of California, Berkeley, California 94720 (United States); Zhang, Jinfeng; Hao, Yue [Key Laboratory of Wide Band Gap Semiconductor Materials and Devices, School of Microelectronics, Xidian University, Xi' an 710071 (China); Wang, Lin-Wang, E-mail: lwwang@lbl.gov [Material Science Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720 (United States)

    2014-01-13

    The band-to-band tunneling of monolayer transition metal dichalcogenides nano-junction is investigated using atomistic ab initio quantum transport simulations. From the simulation, it is found that the transition metal vacancy defect in the two-dimensional MX{sub 2} (M = Mo,W; X = S,Se) band-to-band tunneling diode can dramatically boost the on-state current up to 10 times while maintaining the device sub-threshold swing. The performance enhancement mechanism is discussed in detail by examining partial density of states of the system. It is found that the transition metal vacancy induces band-gap states, which reduce the effective length of the tunneling transition region.

  9. Micromechanics of shear banding

    Energy Technology Data Exchange (ETDEWEB)

    Gilman, J.J.

    1992-08-01

    Shear-banding is one of many instabilities observed during the plastic flow of solids. It is a consequence of the dislocation mechanism which makes plastic flow fundamentally inhomogeneous, and is exacerbated by local adiabatic heating. Dislocation lines tend to be clustered on sets of neighboring glide planes because they are heterogeneously generated; especially through the Koehler multiple-cross-glide mechanism. Factors that influence their mobilities also play a role. Strain-hardening decreases the mobilities within shear bands thereby tending to spread (delocalize) them. Strain-softening has the inverse effect. This paper reviews the micro-mechanisms of these phenomena. It will be shown that heat production is also a consequence of the heterogeneous nature of the microscopic flow, and that dislocation dipoles play an important role. They are often not directly observable, but their presence may be inferred from changes in thermal conductivity. It is argued that after deformation at low temperatures dipoles are distributed a la Pareto so there are many more small than large ones. Instability at upper yield point, the shapes of shear-band fronts, and mechanism of heat generation are also considered. It is shown that strain-rate acceleration plays a more important role than strain-rate itself in adiabatic instability.

  10. The synthesis of hierarchical nanostructured MoS2/Graphene composites with enhanced visible-light photo-degradation property

    Science.gov (United States)

    Zhao, Yongjie; Zhang, Xiaowei; Wang, Chengzhi; Zhao, Yuzhen; Zhou, Heping; Li, Jingbo; Jin, HaiBo

    2017-08-01

    Novel two-dimensional materials with a layered structure are of special interest for a variety of promising applications. Herein, MoS2 and MoS2/Graphene nanocomposite with hierarchical nanostructure were successfully synthesized employing a one-step hydrothermal method. Photo-degradation of methylene blue (MB) and rhodamine (RHB) were adopted to assess the photo-degradation ability of the products. Comparing with bare MoS2, the hierarchical MoS2/Graphene nanocomposite achieved relatively higher degradation rate of 99% in 28 min for MB as well in 50 min for RHB. These results verified that this proposed hierarchical nanocomposite is a good photo-degradation semiconductor. The excellent performance was mainly ascribed to the synergistic effect of MoS2 and graphene layers. The MoS2 possessing a band gap of 1.9 eV would provide abundant electron-hole pairs. The graphene layers with excellent electro-conductivity could realize the quick transport of electrons via its extended π-conjugation structure, consequently benefiting the separation of photo-generated carriers. These findings indicate that the graphene layer is a promising candidate as a co-catalyst for MoS2 photo-catalyst, and also provide useful information for understanding the observed enhanced photocatalytic mechanism in experiments.

  11. Interface designed MoS2/GaAs heterostructure solar cell with sandwich stacked hexagonal boron nitride.

    Science.gov (United States)

    Lin, Shisheng; Li, Xiaoqiang; Wang, Peng; Xu, Zhijuan; Zhang, Shengjiao; Zhong, Huikai; Wu, Zhiqian; Xu, Wenli; Chen, Hongsheng

    2015-10-13

    MoS2 is a layered two-dimensional semiconductor with a direct band gap of 1.8 eV. The MoS2/bulk semiconductor system offers a new platform for solar cell device design. Different from the conventional bulk p-n junctions, in the MoS2/bulk semiconductor heterostructure, static charge transfer shifts the Fermi level of MoS2 toward that of bulk semiconductor, lowering the barrier height of the formed junction. Herein, we introduce hexagonal boron nitride (h-BN) into MoS2/GaAs heterostructure to suppress the static charge transfer, and the obtained MoS2/h-BN/GaAs solar cell exhibits an improved power conversion efficiency of 5.42%. More importantly, the sandwiched h-BN makes the Fermi level tuning of MoS2 more effective. By employing chemical doping and electrical gating into the solar cell device, PCE of 9.03% is achieved, which is the highest among all the reported monolayer transition metal dichalcogenide based solar cells.

  12. Enhanced photocatalytic activity of ZnS nanoparticles loaded with MoS2 nanoflakes by self-assembly approach

    Science.gov (United States)

    Vattikuti, S. V. Prabhakar; Byon, Chan; Jeon, Sora

    2016-12-01

    A hybrid consisting of ZnS nanoparticles supported on layered MoS2-ZnS was synthesized by a hydrothermal method based on self-assembly technique without using a template. XRD, SEM-EDX, TEM, HR-TEM, TG-DTA, XPS, N2 adsorption-desorption, and UV-Vis spectroscopies were used to characterize the structural features, morphology, and composition of the MoS2-ZnS hybrid. The results show that the MoS2-ZnS hybrid is mainly ZnS nanoparticles on layered MoS2 with a thickness of ca. 5-20 nm. The combination of the MoS2 and ZnS hybrid structure is beneficial for enhancing the photocatalytic degradation of rhodamine B (RhB) under visible light irradiation. A possible photoreaction mechanism of the MoS2-ZnS hybrid in the degradation is proposed. The photoexcited electrons from the ZnS could easily transfer to the conduction band of MoS2, thus decreasing the recombination of photoinduced carriers and enabling the degradation of RhB under visible light irradiation.

  13. Mo1-xWxSe2-Based Schottky Junction Photovoltaic Cells.

    Science.gov (United States)

    Yi, Sum-Gyun; Kim, Sung Hyun; Park, Sungjin; Oh, Donggun; Choi, Hwan Young; Lee, Nara; Choi, Young Jai; Yoo, Kyung-Hwa

    2016-12-14

    We developed Schottky junction photovoltaic cells based on multilayer Mo1-xWxSe2 with x = 0, 0.5, and 1. To generate built-in potentials, Pd and Al were used as the source and drain electrodes in a lateral structure, and Pd and graphene were used as the bottom and top electrodes in a vertical structure. These devices exhibited gate-tunable diode-like current rectification and photovoltaic responses. Mo0.5W0.5Se2 Schottky diodes with Pd and Al electrodes exhibited higher photovoltaic efficiency than MoSe2 and WSe2 devices with Pd and Al electrodes, likely because of the greater adjusted band alignment in Mo0.5W0.5Se2 devices. Furthermore, we showed that Mo0.5W0.5Se2-based vertical Schottky diodes yield a power conversion efficiency of ∼16% under 532 nm light and ∼13% under a standard air mass 1.5 spectrum, demonstrating their remarkable potential for photovoltaic applications.

  14. Efficient active waveguiding properties of Mo6 nano-cluster-doped polymer nanotubes

    Science.gov (United States)

    Bigeon, J.; Huby, N.; Amela-Cortes, M.; Molard, Y.; Garreau, A.; Cordier, S.; Bêche, B.; Duvail, J.-L.

    2016-06-01

    We investigate 1D nanostructures based on a Mo6@SU8 hybrid nanocomposite in which photoluminescent Mo6 clusters are embedded in the photosensitive SU8 resist. Tens of micrometers long Mo6@SU8-based tubular nanostructures were fabricated by the wetting template method, enabling the control of the inner and outer diameter to about 190 nm and 240 nm respectively, as supported by structural and optical characterizations. The image plane optical study of these nanotubes under optical pumping highlights the efficient waveguiding phenomenon of the red luminescence emitted by the clusters. Moreover, the wave vector distribution in the Fourier plane determined by leakage radiation microscopy gives additional features of the emission and waveguiding. First, the anisotropic red luminescence of the whole system can be attributed to the guided mode along the nanotube. Then, a low-loss propagation behavior is evidenced in the Mo6@SU8-based nanotubes. This result contrasts with the weaker waveguiding signature in the case of UV210-based nanotubes embedding PFO (poly(9,9-di-n-octylfluorenyl-2,7-diyl)). It is attributed to the strong reabsorption phenomenon, owing to overlapping between absorption and emission bands in the semi-conducting conjugated polymer PFO. These results make this Mo6@SU8 original class of nanocomposite a promising candidate as nanosources for submicronic photonic integration.

  15. Chemisorption-induced n-doping of MoS{sub 2} by oxygen

    Energy Technology Data Exchange (ETDEWEB)

    Qi, Long; Wang, Ying; Wu, Yihong, E-mail: elewuyh@nus.edu.sg [Department of Electrical and Computer Engineering, National University of Singapore, 4 Engineering Drive 3, Singapore, Singapore 117583 (Singapore); Shen, Lei, E-mail: shenlei@nus.edu.sg [Engineering Science Program, Faculty of Engineering, National University of Singapore, Singapore, Singapore 117579 (Singapore)

    2016-02-08

    Both chemisorption and physisorption affect the electronic properties of two-dimensional materials, such as MoS{sub 2}, but it remains a challenge to probe their respective roles experimentally. Through repeated in-situ electrical measurements of few-layer MoS{sub 2} field-effect transistors in an ultrahigh vacuum system with well-controlled oxygen partial pressure (6 × 10{sup −8} mbar–3 × 10{sup −7} mbar), we were able to study the effect of chemisorption on surface defects separately from physically adsorbed oxygen molecules. It is found that chemisorption of oxygen results in n-doping in the channel but negligible effect on mobility and on/off ratio of the MoS{sub 2} transistors. These results are in disagreement with the previous reports on p-doping and degradation of the device's performance when both chemisorption and physisorption are present. Through the analysis of adsorption-desorption kinetics and the first-principles calculations of electronic properties, we show that the experimentally observed n-doping effect originates from dissociative adsorption of oxygen at the surface defects of MoS{sub 2}, which lowers the conduction band edge locally and makes the MoS{sub 2} channel more n-type-like as compared to the as-fabricated devices.

  16. Metallic and ferromagnetic MoS2 nanobelts with vertically aligned edges

    Institute of Scientific and Technical Information of China (English)

    Guanchen Xu[1,2; Xinsheng Wang[1; Yupeng Sun[1; Xiao Chen[2; Jingying Zheng[1; Lifei Sun[1; Liying Jiao[1; Jinghong Li[1

    2015-01-01

    Edge effects are predicted to significantly impact the properties of low dimensional materials with layered structures. The synthesis of low dimensional materials with copious edges is desired for exploring the effects of edges on the band structure and properties of these materials. Here we developed an approach for synthesizing MoS2 nanobelts terminated with vertically aligned edges by sulfurizing hydrothermally synthesized MoO3 nanobelts in the gas phase through a kinetically driven process; we then investigated the electrical and magnetic properties of these metastable materials. These edge-terminated MoS2 nanobelts were found to be metallic and ferromagnetic, and thus dramatically different from the semiconducting and nonmagnetic two-dimensional (2D) and three-dimensional (3D) 2H-MoS2 materials. The transitions in electrical and magnetic properties elucidate the fact that edges can tune the properties of low dimensional materials. The unique structure and properties of this one-dimensional (1D) MoS2 material will enable its applications in electronics, spintronics, and catalysis.

  17. Gorwth and characterization of SrMoO3 thin films

    Institute of Scientific and Technical Information of China (English)

    H.Hs.Wang; D.F.Cui; Y.L.Zhou; Z.H.Chen; F.Chen; T.Zhao; H.B.Lu; G.Z.Y

    2001-01-01

    Highly conductive SrMoO3 thin films with good crystallinity and somooth surface were grown on SrTiO3(001)substrates by pulsed laser deposition.The effects of ubstrate temperature and oxygen pressure on the stucture,Surface morphology,and eletrical properties were studied.In the range of substrate temperatures form 560℃ to 640℃ and oxygen pressure from 10-3 to 10-4 Pa studied in our experiments,high-quality SrMoO3 thin films were produced. Beyond the top temperature or oxygen pressure limit,SrMoO4 appears as an impurity phase.High-resolution transmission electron microscopy(HRTEM) study shows that the SrMoO3 film has high-quality crystallinity and an epitaxial nature.The root-mean-square surface roughness of the film deposited at 2.5×10-4 Pa is 3.9A.The films exhibit metallic conduction,which results from the delocalized electrons from Mo.X-ray photoelectron spectroscopy (XPS) measurements characterized its core level spectra and the valence band.2001 Elsevier Science B.V.All rights reserved.

  18. Zn doped MoO3 nanobelts and the enhanced gas sensing properties to ethanol

    Science.gov (United States)

    Yang, Shuang; Liu, Yueli; Chen, Tao; Jin, Wei; Yang, Tingqiang; Cao, Minchi; Liu, Shunshun; Zhou, Jing; Zakharova, Galina S.; Chen, Wen

    2017-01-01

    Zn doped MoO3 nanobelts with the thickness of 120-275 nm, width of 0.3-1.4 μm and length of more than 100 μm are prepared by hydrothermal reaction. The operating temperature of sensors based on Zn doped MoO3 nanobelts is 100-380 °C with a better response to low concentration of ethanol. The highest response value of sensors based on Zn doped MoO3 to 1000 ppm ethanol at 240 °C is 321, which is about 15 times higher than that of pure MoO3 nanobelts. The gas sensors based on Zn doped MoO3 nanobelts possess good selectivity to ethanol compared with methanol, ammonia, acetone and toluene, which implies that it would be a good candidate in the potential application. The improvement of gas sensing properties may be attributed to the increasing absorbed ethanol, the decreasing probability of ethoxy recombination, the promoted dehydrogenation progress at lower temperature, and the narrowed band gap by Zn doping.

  19. MoS2-clad microfibre laser delivering conventional, dispersion-managed and dissipative solitons

    Science.gov (United States)

    Cui, Yudong; Lu, Feifei; Liu, Xueming

    2016-07-01

    Molybdenum disulfide (MoS2), whose monolayer possesses a direct band gap, displays promising applications in optoelectronics, photonics, and lasers. Recent researches have demonstrated that MoS2 has not only a significant broadband saturable absorption performance, but also a higher optical nonlinear response than graphene. However, MoS2 shows much lower optical damage threshold owing to the poorer thermal conductivity and mechanical property. Here, we exploit a MoS2-clad microfibre (MCM) as the saturable absorber (SA) for the generation of ultrashort pulses under different dispersion conditions. The improved evanescent field interaction scheme can overcome the laser-induced thermal damage, as well as take full advantage of the strong nonlinear effect of MoS2. With the MCM SA, conventional, dispersion-managed, and dissipative solitons are generated around 1600 nm in Er-doped fibre lasers with anomalous, near-zero, and normal cavity dispersions, respectively. Our work paves the way for applications of 2D layered materials in photonics, especially in laser sources.

  20. MoS2-clad microfibre laser delivering conventional, dispersion-managed and dissipative solitons

    Science.gov (United States)

    Cui, Yudong; Lu, Feifei; Liu, Xueming

    2016-01-01

    Molybdenum disulfide (MoS2), whose monolayer possesses a direct band gap, displays promising applications in optoelectronics, photonics, and lasers. Recent researches have demonstrated that MoS2 has not only a significant broadband saturable absorption performance, but also a higher optical nonlinear response than graphene. However, MoS2 shows much lower optical damage threshold owing to the poorer thermal conductivity and mechanical property. Here, we exploit a MoS2-clad microfibre (MCM) as the saturable absorber (SA) for the generation of ultrashort pulses under different dispersion conditions. The improved evanescent field interaction scheme can overcome the laser-induced thermal damage, as well as take full advantage of the strong nonlinear effect of MoS2. With the MCM SA, conventional, dispersion-managed, and dissipative solitons are generated around 1600 nm in Er-doped fibre lasers with anomalous, near-zero, and normal cavity dispersions, respectively. Our work paves the way for applications of 2D layered materials in photonics, especially in laser sources. PMID:27456468

  1. Introducing DInaMo: A Package for Calculating Protein Circular Dichroism Using Classical Electromagnetic Theory.

    Science.gov (United States)

    Uporov, Igor V; Forlemu, Neville Y; Nori, Rahul; Aleksandrov, Tsvetan; Sango, Boris A; Mbote, Yvonne E Bongfen; Pothuganti, Sandeep; Thomasson, Kathryn A

    2015-09-07

    The dipole interaction model is a classical electromagnetic theory for calculating circular dichroism (CD) resulting from the π-π* transitions of amides. The theoretical model, pioneered by J. Applequist, is assembled into a package, DInaMo, written in Fortran allowing for treatment of proteins. DInaMo reads Protein Data Bank formatted files of structures generated by molecular mechanics or reconstructed secondary structures. Crystal structures cannot be used directly with DInaMo; they either need to be rebuilt with idealized bond angles and lengths, or they need to be energy minimized to adjust bond lengths and bond angles because it is common for crystal structure geometries to have slightly short bond lengths, and DInaMo is sensitive to this. DInaMo reduces all the amide chromophores to points with anisotropic polarizability and all nonchromophoric aliphatic atoms including hydrogens to points with isotropic polarizability; all other atoms are ignored. By determining the interactions among the chromophoric and nonchromophoric parts of the molecule using empirically derived polarizabilities, the rotational and dipole strengths are determined leading to the calculation of CD. Furthermore, ignoring hydrogens bound to methyl groups is initially explored and proves to be a good approximation. Theoretical calculations on 24 proteins agree with experiment showing bands with similar morphology and maxima.

  2. Free-standing electronic character of monolayer MoS2 in van der Waals epitaxy

    Science.gov (United States)

    Kim, HoKwon; Dumcenco, Dumitru; Frégnaux, Mathieu; Benayad, Anass; Chen, Ming-Wei; Kung, Yen-Cheng; Kis, Andras; Renault, Olivier

    2016-08-01

    We have evaluated as-grown Mo S2 crystals, epitaxially grown on a monocrystalline sapphire by chemical vapor deposition (CVD), with direct electronic band-structure measurements by energy-filtered k -space photoelectron emission microscopy performed with a conventional laboratory vacuum ultraviolet He I light source under off-normal illumination. The valence states of the epitaxial Mo S2 were mapped in momentum space down to 7 eV below the Fermi level. Despite the high nucleation density within the imaged area, the CVD Mo S2 possesses an electronic structure similar to the free-standing monolayer Mo S2 single crystal, and it exhibits hole effective masses of 2.41 ±0.05 m0 , and 0.81 ±0.05 m0 , respectively, at Γ and K high-symmetry points that are consistent with the van der Waals epitaxial growth mechanism. This demonstrates the excellent ability of the Mo S2 CVD on sapphire to yield a highly aligned growth of well-stitched grains through epitaxial registry with a strongly preferred crystallographic orientation.

  3. Recent advances in MoS2 nanostructured materials for energy and environmental applications - A review

    Science.gov (United States)

    Theerthagiri, J.; Senthil, R. A.; Senthilkumar, B.; Reddy Polu, Anji; Madhavan, J.; Ashokkumar, Muthupandian

    2017-08-01

    Molybdenum disulfide (MoS2), a layered transition metal dichalcogenide with an analogous structure to graphene, has attracted enormous attention worldwide owing to its use in a variety of applications such as energy storage, energy conversion, environmental remediation and sensors. MoS2 and graphene have almost similar functional properties such as high charge carrier transport, high wear resistance and good mechanical strength and friction. However, MoS2 is advantageous over graphene due to its low-cost, abundancy, tailorable morphologies and tuneable band gap with good visible light absorption properties. In this review, we have focussed mainly on recent advances in MoS2 nanostructured materials for the applications in the broad area of energy and environment. Special attention has been paid to their applications in dye-sensitized solar cells, supercapacitor, Li-ion battery, hydrogen evolution reaction, photocatalysis for the degradation of organic pollutants, chemical/bio sensors and gas sensors. Finally, the challenges to design MoS2 nanostructures suitable for energy and environmental applications are also highlighted.

  4. Switching Properties and Phase Transition Mechanism of Mo6+-Doped Vanadium Dioxide Thin Films

    Institute of Scientific and Technical Information of China (English)

    XU Shi-Qing; MA Hong-Ping; DAI Shi-Xun; JIANG Zhong-Hong

    2003-01-01

    Using V2O5 and MOO3 powders as precursors, a novel preparation method, i.e., the so-called inorganic sol-gel, is developed to synthesize Mo6+-doped vanadium dioxide (VO?) thin films. The structure, valence state, phase transition temperature and magnitude of resistivity change are characterized by x-ray diffraction, x-ray photoelectron spectroscopy and the four-point equipment. The results show that the main chemical composition of doped thin 61ms was VO2, the structure ofMoOa in doped thin films did not change, and the phase transition temperature of doped thin Sims was obviously lowered with the increasing MoOs doped concentration, but the magnitude of resistivity change was also decreased. However, so long as MoOs doped concentration was not more than 5 wt. %, the magnitude of resistivity change of doped thin Glms still reached more 2 orders. The analysis show that MoOs dissolved in crystal structure of VO-z formed the donor defect MOJ and then reduced the forbidden-band width, which lowered the phase transition temperature. Consequently it was widened applications of the VO2 thin films.

  5. Introducing DInaMo: A Package for Calculating Protein Circular Dichroism Using Classical Electromagnetic Theory

    Directory of Open Access Journals (Sweden)

    Igor V. Uporov

    2015-09-01

    Full Text Available The dipole interaction model is a classical electromagnetic theory for calculating circular dichroism (CD resulting from the π-π* transitions of amides. The theoretical model, pioneered by J. Applequist, is assembled into a package, DInaMo, written in Fortran allowing for treatment of proteins. DInaMo reads Protein Data Bank formatted files of structures generated by molecular mechanics or reconstructed secondary structures. Crystal structures cannot be used directly with DInaMo; they either need to be rebuilt with idealized bond angles and lengths, or they need to be energy minimized to adjust bond lengths and bond angles because it is common for crystal structure geometries to have slightly short bond lengths, and DInaMo is sensitive to this. DInaMo reduces all the amide chromophores to points with anisotropic polarizability and all nonchromophoric aliphatic atoms including hydrogens to points with isotropic polarizability; all other atoms are ignored. By determining the interactions among the chromophoric and nonchromophoric parts of the molecule using empirically derived polarizabilities, the rotational and dipole strengths are determined leading to the calculation of CD. Furthermore, ignoring hydrogens bound to methyl groups is initially explored and proves to be a good approximation. Theoretical calculations on 24 proteins agree with experiment showing bands with similar morphology and maxima.

  6. Getting nanometric MoO{sub 3} through chemical synthesis and high energy milling

    Energy Technology Data Exchange (ETDEWEB)

    Santos-Beltrán, M. [Centro de Investigación en Materiales Avanzados (CIMAV), Laboratorio Nacional de Nanotecnología, Miguel de Cervantes No. 120, C.P. 31136 Chihuahua, Chih. (Mexico); Paraguay-Delgado, F., E-mail: francisco.paraguay@cimav.edu.mx [Centro de Investigación en Materiales Avanzados (CIMAV), Laboratorio Nacional de Nanotecnología, Miguel de Cervantes No. 120, C.P. 31136 Chihuahua, Chih. (Mexico); Santos-Beltrán, A. [Universidad Tecnológica de Chihuahua Sur, Km. 3 Carretera Chihuahua a Aldama s/n, C.P. 31050 Chihuahua, Chih. (Mexico); Fuentes, L. [Centro de Investigación en Materiales Avanzados (CIMAV), Laboratorio Nacional de Nanotecnología, Miguel de Cervantes No. 120, C.P. 31136 Chihuahua, Chih. (Mexico)

    2015-11-05

    The effects of high energy mechanical milling (HEMM) were studied on the microstructure and optical properties of MoO{sub 3} for hexagonal and orthorhombic phases. Employing HEMM was possible change particle size as a function of mechanical milling time, as well as the small quantity transformation percentage from hexagonal to orthorhombic phase. The relationship between microstrain and optical properties generated was studied. The electronic structures were calculated using the Density Functional Theory (DFT); to determinate partial density of state (PDOS). Band gap structure calculations show a good correlation between experimental and simulated data. The approximated values of microstrain, particle size, lattice parameters and oxygen vacancies were obtained employing the Rietveld refinement of X-ray diffraction patterns. Samples were characterized by electron microscopy techniques, surface area analysis (BET), thermal-gravimetric analysis (TGA), differential scanning calorimetry (DSC) and ultraviolet–visible spectroscopy (UV–Vis). It was possible, obtain particles with size below 40 nm by 30 min milling. - Graphical abstract: Orthorhombic phase, SEM image, SAED before milling, milling NPs, Particle size and band gap variation by milling time. - Highlights: • MoO{sub 3} with hexagonal and orthorhombic structures was synthesized selectively. • By milling short time (30 m), it was possible get 40 nm diameter particles. • The band gap decrease for nanoparticles, then corroborated by simulation. • MoO{sub 3} nanoparticles get high surface area for new technologic applications.

  7. Anomalous photoluminescence thermal quenching of sandwiched single layer MoS_2

    KAUST Repository

    Tangi, Malleswara

    2017-09-22

    We report an unusual thermal quenching of the micro-photoluminescence (µ-PL) intensity for a sandwiched single-layer (SL) MoS2. For this study, MoS2 layers were chemical vapor deposited on molecular beam epitaxial grown In0.15Al0.85N lattice matched templates. Later, to accomplish air-stable sandwiched SL-MoS2, a thin In0.15Al0.85N cap layer was deposited on the MoS2/In0.15Al0.85N heterostructure. We confirm that the sandwiched MoS2 is a single layer from optical and structural analyses using µ-Raman spectroscopy and scanning transmission electron microscopy, respectively. By using high-resolution X-ray photoelectron spectroscopy, no structural phase transition of MoS2 is noticed. The recombination processes of bound and free excitons were analyzed by the power-dependent µ-PL studies at 77 K and room temperature (RT). The temperature-dependent micro photoluminescence (TDPL) measurements were carried out in the temperature range of 77 – 400 K. As temperature increases, a significant red-shift is observed for the free-exciton PL peak, revealing the delocalization of carriers. Further, we observe unconventional negative thermal quenching behavior, the enhancement of the µ-PL intensity with increasing temperatures up to 300K, which is explained by carrier hopping transitions that take place between shallow localized states to the band-edges. Thus, this study renders a fundamental insight into understanding the anomalous thermal quenching of µ-PL intensity of sandwiched SL-MoS2.

  8. Development of fission Mo-99 production technology

    Energy Technology Data Exchange (ETDEWEB)

    Park, Jin Ho; Choung, W. M.; Lee, K. I. and others

    2001-05-01

    This R and D project is planed to supply domestic demands of Mo-99 through fission route, and consequently this project will be expected to rise up utilization of HANARO and KAERI's capability for marketing extension into domestic and oversea radiopharmaceutical market. HEU and LEU target types are decided and designed for fission Mo-99 production in domestic. Experimental study of target fabrication technology was performed and developed processing equipments. And conceptual design of target loading/unloading in/from HANARO device are performed. Tracer test of Mo-99 separation and purification process was performed, test results reach to Mo-99 recovery yield above 80% and decontamination factor above 1600. Combined Mo-99 separation and purification process was decided for hot test scheduled from next year, and performance test was performed. Conceptual design for modification of existing hot cell for fission Mo-99 production facility was performed and will be used for detail design. Assumption for the comparison of LEU and HEU target in fission Mo-99 production process were suggested and compared of merits and demerits in view of fabrication technology and economy feasibility.

  9. Synthesized MoSe2/TiO2 heterogeneous structure as the promising photocatalytic material: Studies from theory to experiment

    Science.gov (United States)

    Lei, Xiang; Yu, Ke; Tang, Zheng; Zhu, Ziqiang

    2017-01-01

    An excellent photocatalyst has been successfully achieved by synthesizing a MoSe2/TiO2 heterostructure. The density functional theory was employed to accurately describe the impact of composited MoSe2 by comparing the electronic structure, band position, and distribution of charge carriers between the MoSe2/TiO2 heterostructure and bare TiO2/MoSe2. The calculation results illustrate that the inhibitory effect of the electron-hole pair recombination can be promoted in the obtained heterostructure, which was experimentally verified by photoluminescence. The photodegradation of methylene blue demonstrated that the enhanced photocatalysis originates from the modulated carrier behavior due to MoSe2 composition. This work presents a good candidate for the application of the photocatalytic process and enriches our understanding of the electronic structure of TMDs-/TiO2-based heterojunction composites.

  10. Two-dimensional semiconductor HfSe{sub 2} and MoSe{sub 2}/HfSe{sub 2} van der Waals heterostructures by molecular beam epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Aretouli, K. E.; Tsipas, P.; Tsoutsou, D.; Marquez-Velasco, J.; Xenogiannopoulou, E.; Giamini, S. A.; Vassalou, E.; Kelaidis, N.; Dimoulas, A., E-mail: a.dimoulas@inn.demokritos.gr [Institute of Nanoscience and Nanotechnology, National Center for Scientific Research “Demokritos,” 15310, Aghia Paraskevi, Athens (Greece)

    2015-04-06

    Using molecular beam epitaxy, atomically thin 2D semiconductor HfSe{sub 2} and MoSe{sub 2}/HfSe{sub 2} van der Waals heterostructures are grown on AlN(0001)/Si(111) substrates. Details of the electronic band structure of HfSe{sub 2} are imaged by in-situ angle resolved photoelectron spectroscopy indicating a high quality epitaxial layer. High-resolution surface tunneling microscopy supported by first principles calculations provides evidence of an ordered Se adlayer, which may be responsible for a reduction of the measured workfunction of HfSe{sub 2} compared to theoretical predictions. The latter reduction minimizes the workfunction difference between the HfSe{sub 2} and MoSe{sub 2} layers resulting in a small valence band offset of only 0.13 eV at the MoSe{sub 2}/HfSe{sub 2} heterointerface and a weak type II band alignment.

  11. The Wulf bands of oxygen

    Science.gov (United States)

    Bernath, Peter; Carleer, Michel; Fally, Sophie; Jenouvrier, Alain; Vandaele, Ann Carine; Hermans, Christian; Mérienne, Marie-France; Colin, Reginald

    1998-11-01

    The Wulf bands of oxygen in the 240-290 nm spectral region are caused by collision-induced absorption of the Herzberg III ( A' 3Δu- X3Σ-g) system. These bands had been previously attributed to the oxygen dimer, (O 2) 2. Under atmospheric conditions the Wulf bands are thus the long-wavelength extension of the Herzberg continuum. Absorption of solar radiation by the Wulf bands may be an additional source of NO in the stratosphere.

  12. Semiconductors bonds and bands

    CERN Document Server

    Ferry, David K

    2013-01-01

    As we settle into this second decade of the twenty-first century, it is evident that the advances in micro-electronics have truly revolutionized our day-to-day lifestyle. The technology is built upon semiconductors, materials in which the band gap has been engineered for special values suitable to the particular application. This book, written specifically for a one semester course for graduate students, provides a thorough understanding of the key solid state physics of semiconductors. It describes how quantum mechanics gives semiconductors unique properties that enabled the micro-electronics revolution, and sustain the ever-growing importance of this revolution.

  13. Evidence for shape coexistence in $^{98}$Mo

    CERN Document Server

    Thomas, T; Werner, V; Ahn, T; Cooper, N; Duckwitz, H; Hinton, M; Ilie, G; Jolie, J; Petkov, P; Radeck, D

    2013-01-01

    A $\\gamma\\gamma$ angular correlation experiment has been performed to investigate the low-energy states of the nucleus $^{98}$Mo. The new data, including spin assignments, multipole mixing ratios and lifetimes reveal evidence for shape coexistence and mixing in $^{98}$Mo, arising from a proton intruder configuration. This result is reproduced by a theoretical calculation within the proton-neutron interacting boson model with configuration mixing, based on microscopic energy density functional theory. The microscopic calculation indicates the importance of the proton particle-hole excitation across the Z=40 sub-shell closure and the subsequent mixing between spherical vibrational and the $\\gamma$-soft equilibrium shapes in $^{98}$Mo.

  14. Dispersion-Corrected Density Functional Theory Investigations of Structural and Electronic Properties of Bulk MoS2: Effect of Uniaxial Strain.

    Science.gov (United States)

    Nguyen, Chuong V; Hieu, Nguyen N; Nguyen, Duong T

    2015-12-01

    Strain-dependent structural and electronic properties of MoS2 materials are investigated using first principles calculations. The structural and electronic band structures of the MoS2 with relaxed unit cells are optimized and calculated by the dispersion-corrected density functional theory (DFT-D2). Calculations within the local density approximation (LDA) and GGA using PAW potentials were also performed for specific cases for the purpose of comparison. The effect of strain on the band gap and the dependence of formation energy on strain of MoS2 are also studied and discussed using the DFT-D2 method. In bulk MoS2, the orbitals shift towards the higher/lower energy area when strain is applied along the z/x direction, respectively. The energy splitting of Mo4d states is in the range from 0 to 2 eV, which is due to the reduction of the electronic band gap of MoS2.

  15. Absorption enhancement in CH3NH3PbI3 solar cell using a TiO2/MoS2 nanocomposite electron selective contact

    Science.gov (United States)

    Imran Ahmed, Muhammad; Hussain, Zakir; Khalid, Amir; Noman Amin, Hafiz Muhammad; Habib, Amir

    2016-04-01

    In the present contribution, perovskite absorbers have been combined with few layer thick MoS2 semiconductor to put together a solar cell allowing broad spectrum harvesting of solar radiations. Such modification allows to achieve solar light harvesting at the band edges, addressing a drawback of CH3NH3PbI3 absorbers. We recorded an improved efficiency from 3.7% to 4.3% on the back of this methodology. We have also worked out a novel methodology to synthesize TiO2/MoS2 nanocomposite by in situ dispersion of liquid exfoliated MoS2 sheets in the sol gel reaction.

  16. Structural and photoluminescence properties of Tb-doped CaMoO{sub 4} nanoparticles with sequential surface coatings

    Energy Technology Data Exchange (ETDEWEB)

    Ansari, Anees A., E-mail: aneesaansari@gmail.com [King Abdullah Institute for Nanotechnology, King Saud University, P.O. Box 2455, Riyadh 11451 (Saudi Arabia); Parchur, A.K. [Department of Physics, Banaras Hindu University, Varanasi 221005 (India); Alam, M. [Research Center, College of Science, King Saud University, P.O. Box 2455, Riyadh (Saudi Arabia); Azzeer, Abdallah [King Abdullah Institute for Nanotechnology, King Saud University, P.O. Box 2455, Riyadh 11451 (Saudi Arabia)

    2014-10-15

    The crystal structure, surface chemistry and optical properties of Tb-doped CaMoO{sub 4} (CaMoO{sub 4}:Tb) nanoparticles and the sequentially coated CaMoO{sub 4}:Tb@CaMoO{sub 4} and CaMoO{sub 4}:Tb@CaMoO{sub 4}@SiO{sub 2} nanostructures have been characterized by X-ray diffraction (XRD), Thermo-gravimetric analysis (TGA), UV–vis absorption (UV–Vis), Fourier- transform infrared spectroscopy (FT-IR), Raman spectroscopy and Photoluminescence spectroscopy. The XRD results indicate that the obtained CaMoO{sub 4}:Tb is sheelite tetragonal structure and well crystallized at 150 °C. The particle size increases from 21 to 48 nm by sequential coating of CaMoO{sub 4} and silica formation around the surface of core nanoparticles. These nanocrystals were well-dispersed in aqueous and non-aqueous solvents to form clear colloidal solutions. The colloidal solutions of three samples show well characteristic optical absorption band in UV/Visible region. The surface coating on core particles will significantly influence the structural and photoluminescence properties. The as-prepared core nanoparticles showed high photoluminescence as compared to surface coated core–shell nanoparticles because Tb{sup 3+} ion located at the particle surface. Absorption and luminescence spectroscopic studies have been examined for future application in the development of optical devices as well as optical bioprobes. - Highlights: • Low temperature synthesis process for preparation of core and core–shell nanoparticles. • Chemically, thermally stable core and core–shell nanoparticles highly dispersed in aqueous media. • Effect of surface coating on structural, optical and luminescence properties of CaMoO{sub 4};Tb nanoparticles. • Silica surface modified core–shell nanoparticles could be consider as alternative luminescent bioprobes.

  17. Self-assembly and enhanced visible-light-driven photocatalytic activities of Bi2MoO6 by tungsten substitution

    Science.gov (United States)

    Yu, Hongguang; Zhu, Zhenfeng; Zhou, Jianhong; Wang, Jing; Li, Junqi; Zhang, Yanli

    2013-01-01

    The different compositions of Bi2MoO6 by tungsten substitution have been successfully synthesized via a facile hydrothermal process in the absence of a surfactant. All W-doped Bi2MoO6 samples were composed of nanosheets with similar orthorhombic Aurivillius layered structures. Bi2MoO6 samples show different phases varied with W content. For the Bi2MoO6 samples with the different nw values, their band gaps have changed obviously compared with Bi2MoO6 (2.69 eV) and Bi2WO6 (2.75 eV). The Bi2MoO6 by tungsten substitution exhibited good photocatalytic activity in degradation of Rhodamine-B under 500 W Xe lamp light irradiation. When nw value is 0.5, the sample has the highest photocatalytic activity for RhB photodecomposition under visible light irradiation. It shows that photocatalytic activities of Bi2MoO6 samples by W substitution are relevant to nanosheet morphology and size, the intrinsic layered structure, band gap and the W content.

  18. Strain-induced giant second-harmonic generation in monolayered 2H-MoX2 (X = S, Se, Te)

    Science.gov (United States)

    Rhim, S. H.; Kim, Yong Soo; Freeman, A. J.

    2015-12-01

    Dynamic second-order nonlinear susceptibilities, χ(2)(2 ω,ω,ω)≡χ(2)(ω) , are calculated here within a fully first-principles scheme for monolayered molybdenum dichalcogenides, 2H-MoX2 (X = S, Se, and Te). The absolute values of χ(2)(ω) across the three chalcogens critically depend on the band gap energies upon uniform strain, yielding the highest χ(2)(0 )˜140 pm/V for MoTe2 in the static limit. Under this uniform in-plane stress, 2H-MoX2 can undergo direct-to-indirect transition of band gaps, which in turn substantially affects χ(2)(ω) . The tunability of χ(2)(ω) by either compressive or tensile strain is demonstrated especially for two important experimental wavelengths, 1064 nm and 800 nm, where resonantly enhanced non-linear effects can be exploited: χ(2) of MoSe2 and MoTe2 approach ˜800 pm/V with -2% strain at 1064 nm.

  19. Doping induced grain size reduction and photocatalytic performance enhancement of SrMoO4:Bi3+

    Science.gov (United States)

    Wang, Yunjian; Xu, Hui; Shao, Congying; Cao, Jing

    2017-01-01

    Ion doping is one of the most effective ways to develop photocatalysts by creating impurity levels in the energy band structure. In this paper, novel Bi3+ doped SrMoO4 (SrMoO4:Bi3+) nanocrystals were prepared by a simple hydrothermal method. By systematic characterizations using x-ray diffraction, infrared spectra, UV-vis spectra, X-ray photoelectron spectroscopy and transmission electron microscopy, it is demonstrated that all the samples crystallized in a single phase of scheelite structure, and particle sizes of SrMoO4:Bi3+ gradually decreased. The Bi3+ doped nanoparticles showed lattice contraction, and band-gap narrowing. The photocatalytic activity of the samples was measured by monitoring the degradation of methylene blue dye in an aqueous solution under UV-radiation exposure. It is found that SrMoO4:Bi3+ showed excellent activity toward photodegradation of methylene blue solution under UV light irradiation compared to the pure SrMoO4. These observations are interpreted in terms of the Bi3+ doping effects and the increased the surface active sites, which results in the improved the ratio of surface charge carrier transfer rate and reduced the electron-hole recombination rate. These results illustrate the potential of particle size and surface defect regulation for the construction of novel semiconductor oxide photocatalysts by ion doping.

  20. Moiré-related in-gap states in a twisted MoS2/graphite heterojunction

    KAUST Repository

    Lu, Chun-I

    2017-07-21

    This report presents a series of low-temperature (4.5 K) scanning tunneling microscopy and spectroscopy experimental results on monolayer MoS2 deposited on highly oriented pyrolytic graphite using chemical vapor deposition. To reveal the detailed connection between atomic morphology and conductivity in twisted MoS2/graphite heterojunctions, we employ high-sensitivity tunneling spectroscopy measurements by choosing a reduced tip-sample distance. We discern previously unobserved conductance peaks within the band gap range of MoS2, and by comparing the tunneling spectra from MoS2 grains of varying rotation with respect to the substrate, show that these features have small but non-negligible dependence on the moiré superstructure. Furthermore, within a single moiré supercell, atomically resolved tunneling spectroscopy measurements show that the spectra between the moiré high and low areas are also distinct. These in-gap states are shown to have an energy shift attributed to their local lattice strain, matching corresponding behavior of the conduction band edge, and we therefore infer that these features are intrinsic to the density of states, rather than experimental artifacts, and attribute them to the twisted stacking and local strain energy of the MoS2/graphite heterointerface.

  1. Floodplain Mapping Submission for Oregon County, MO

    Data.gov (United States)

    Federal Emergency Management Agency, Department of Homeland Security — The Floodplain Mapping study deliverables depict and quantify the flood risks for Oregon County, MO. The City of Thayer and the Missouri State Emergency Management...

  2. 78 FR 45283 - Missouri Disaster #MO-00066

    Science.gov (United States)

    2013-07-26

    ... From the Federal Register Online via the Government Publishing Office SMALL BUSINESS ADMINISTRATION Missouri Disaster MO-00066 AGENCY: U.S. Small Business Administration. ACTION: Notice. SUMMARY... adversely affected by the disaster: Primary Counties: Barton; Callaway; Cape Girardeau; Chariton;...

  3. Phase transformations in Mo-doped FINEMETs

    Energy Technology Data Exchange (ETDEWEB)

    Silveyra, Josefina M., E-mail: jsilveyra@fi.uba.a [Lab. de Solidos Amorfos, INTECIN, FIUBA-CONICET, Paseo Colon 850, (C1063ACV) Buenos Aires (Argentina); Illekova, Emilia; Svec, Peter; Janickovic, Dusan [Institute of Physics SAS, Dubravska cesta 9, 845 11 Bratislava (Slovakia); Rosales-Rivera, Andres [Laboratorio de Magnetismo y Materiales Avanzados, Facultad de Ciencias Exactas y Naturales, Universidad Nacional de Colombia, Manizales (Colombia); Cremaschi, Victoria J. [Lab. de Solidos Amorfos, INTECIN, FIUBA-CONICET, Paseo Colon 850, (C1063ACV) Buenos Aires (Argentina)

    2010-06-15

    In this paper, the phase transformations occurring during the crystallization process of FINEMETs in which Nb has been gradually replaced by Mo have been studied by a variety of techniques including DSC, DTA, TGA, XRD and TEM. The thermal stability of the alloy was deteriorated as a consequence of Mo's smaller atomic size. The gradual replacement of Nb by Mo reduced the onset temperature of Fe-Si and of the borides. The Curie temperature of the amorphous phase slightly decreased from 594 K for x=0 to 587 K for x=3. The borides compounds Fe{sub 2}B and Fe{sub 23}B{sub 6} as well as the (Nb,Mo){sub 5}Si{sub 3} phase were found to precipitate in the second and third crystallization.

  4. Tl2Mo9Se11

    Directory of Open Access Journals (Sweden)

    Patrick Gougeon

    2010-08-01

    Full Text Available The structure of Tl2Mo9Se11, dithallium nonamolybdenum undecaselenide, is isotypic with Tl2Mo9S11 [Potel et al. (1980. Acta Cryst. B36, 1319–1322]. The structural set-up is characterized by a mixture of Mo6Sei8Sea6 and Mo12Sei14Sea6 cluster units in a 1:1 ratio. Both components are interconnected through interunit Mo—Se bonds. The cluster units are centered at Wyckoff positions 3a and 3b (point-group symmetry overline{3}.. The two TlI atoms are situated in the voids of the three-dimensional arrangement. Two of the five independent Se atoms and the Tl atoms lie on sites with 3. symmetry (Wyckoff site 6c.

  5. Morphologies of omega band auroras

    Science.gov (United States)

    Sato, Natsuo; Yukimatu, Akira Sessai; Tanaka, Yoshimasa; Hori, Tomoaki

    2017-08-01

    We examined the morphological signatures of 315 omega band aurora events observed using the Time History of Events and Macroscale Interactions during Substorm ground-based all-sky imager network over a period of 8 years. We find that omega bands can be classified into the following three subtypes: (1) classical (O-type) omega bands, (2) torch or tongue (T-type) omega bands, and (3) combinations of classical and torch or tongue (O/T-type) omega bands. The statistical results show that T-type bands occur the most frequently (45%), followed by O/T-type bands (35%) and O-type bands (18%). We also examined the morphologies of the omega bands during their formation, from the growth period to the declining period through the maximum period. Interestingly, the omega bands are not stable, but rather exhibit dynamic changes in shape, intensity, and motion. They grow from small-scale bumps (seeds) at the poleward boundary of preexisting east-west-aligned auroras, rather than via the rotation or shear motion of preexisting east-west-aligned auroras, and do not exhibit any shear motion during the periods of auroral activity growth. Furthermore, the auroral luminosity is observed to increase during the declining period, and the total time from the start of the growth period to the end of the declining period is found to be about 20 min. Such dynamical signatures may be important in determining the mechanism responsible for omega band formation.

  6. Reaction mechanism of core-shell MoO2/MoS2 nanoflakes via plasma-assisted sulfurization of MoO3

    Science.gov (United States)

    Kumar, Prabhat; Singh, Megha; Sharma, Rabindar K.; Reddy, G. B.

    2016-05-01

    The sulfurization of MoO3 in an H2S/Ar plasma atmosphere has been experimentally studied and a reaction mechanism has been proposed based on the results obtained. Nanostructured thin films (NTFs) of MoO3 were sulfurized at different temperatures varying from 150 °C to 550 °C. High-resolution transmission electron microscopy (TEM) images depict core-shell nanoflakes with varying shell thicknesses as the sulfurization temperature (T sn) is varied. The shells consist of MoS2 and the core is MoO2/MoO3. X-ray diffraction (XRD) and Raman analysis have been used to study the structural changes as MoO3 is sulfurized. The analyses showed two phases, MoO2 and MoS2, at low temperatures (≤350 °C), whereas the films sulfurized at higher temperatures show predominantly MoS2. The scanning electron microscopy (SEM) results show no noticeable changes in the surface morphology of the NTFs after sulfurization. X-ray photoelectron spectroscopy (XPS) was carried out to calculate the relative percentages of MoO3, MoO2 and MoS2. It is revealed that sulfurization of MoO3 in the plasma is affected by T sn. The sulfurization process occurs in two steps, involving the reduction of MoO3 to form MoO2 in the first step, followed by MoO2 being converted into MoS2. It is also evident that the reduction of MoO3 is more a result of the reactive species of hydrogen (H*) than the replacement of oxygen by sulfur in the second step.

  7. Mechanism for Curie temperature variation in La{sub x}Sr{sub 2-x}FeMoO{sub 6} and Ca{sub x}Sr{sub 2-x}FeMoO{sub 6}

    Energy Technology Data Exchange (ETDEWEB)

    Frontera, C.; Rubi, D.; Navarro, J.; Garcia-Munoz, J.L.; Ritter, C.; Fontcuberta, J

    2004-07-15

    By means of high-resolution neutron powder diffraction at 10 K, we have characterized the structural details of La{sub x}Sr{sub 2-x}FeMoO{sub 6} (0{<=}x{<=}0.5) and Ca{sub x}Sr{sub 2-x}FeMoO{sub 6} (0{<=}x{<=}0.6) series of compounds. The Curie temperature (T{sub C}) raises in the La series and slightly decreases in the Ca one. The enhancement of T{sub C} in the La series is attributed to the effect of the conduction band-filling when doping with La.

  8. Stable and Vibrational Octupole Modes in Mo, Xe, Ba, La, Ce and Nd

    Energy Technology Data Exchange (ETDEWEB)

    Gore, P.M.; Hamilton, J.H.; Hwang, J.K.; Jones, E.F.; Peker, L.K.; Ramayya, A.V.; Zhang, X.Q.; Zhu, S.J.

    1998-05-18

    Evidence is presented for stable octupole deformation in neutron-rich nuclei, bounded by Z = 54-58 and N = 85-92. To either side of this region negative parity bands built on more vibrational type octupole modes are observed in {sup 140}Ba and {sup 152,154}Nd. The largest stable octupole deformation ({beta}{sub s} {approximately} 0.1) is found in {sup 144}Ba{sub as}. The theoretically predicted quenching ({beta}{sub s} {approximately} 0) of stable octupole deformation at higher spins is found in {sup 140}Ba. There is good agreement between theory and experiment for the strongly varying electric dipole moments as a function of mass for {sup 142-141}Ba. In odd-A {sup 142}Ba and odd-Z {sup 140}La, we observe parity doublets, two pairs of positive and negative parity bands with opposite spins. In {sup 145}La a strong coupled ground band with symmetric shape coexists with the asymmetric octupole shape which stabilizes above about spin 19/2. In {sup 145,147}La a strong reduction in E2 strength around 25/2 from band crossing is observed. The isotope {sup 109}Mo was identified and a new region of stable uctpole deformation is identified in {sup 107,108}Mo centered around N = 64-66 as earlier predicted. This is the first case of stable uctpole deformation involving only one pair of orbitals.

  9. Wide Band Artificial Pulsar

    Science.gov (United States)

    Parsons, Zackary

    2017-01-01

    The Wide Band Artificial Pulsar (WBAP) is an instrument verification device designed and built by the National Radio Astronomy Observatory (NRAO) in Green Bank, West Virgina. The site currently operates the Green Bank Ultimate Pulsar Processing Instrument (GUPPI) and the Versatile Green Bank Astronomical Spectrometer (VEGAS) digital backends for their radio telescopes. The commissioning and continued support for these sophisticated backends has demonstrated a need for a device capable of producing an accurate artificial pulsar signal. The WBAP is designed to provide a very close approximation to an actual pulsar signal. This presentation is intended to provide an overview of the current hardware and software implementations and to also share the current results from testing using the WBAP.

  10. Mo100 to Mo99 Target Cooling Enhancements Report

    Energy Technology Data Exchange (ETDEWEB)

    Woloshun, Keith Albert [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Dale, Gregory E. [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Olivas, Eric Richard [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Mocko, Michal [Los Alamos National Lab. (LANL), Los Alamos, NM (United States)

    2016-02-16

    Target design requirements changed significantly over the past year to a much higher beam current on larger diameter disks, and with a beam impingement on both ends of the target. Scaling from the previous design, that required significantly more mass flow rate of helium coolant, and also thinner disks. A new Aerzen GM12.4 blower was selected that can deliver up to 400 g/s at 400 psi, compared to about 100 g/s possible with the Tuthill blower previously selected.Further, to accommodate the 42 MeV, 2.7 mA beam on each side of the target, the disk thickness and the coolant gaps were halved to create the current baseline design: 0.5 mm disk thickness (at 29 mm diameter) and 0.25 mm coolant gap. Thermal-hydraulic analysis of this target, presented below for reference, gave very good results, suggesting that the target could be improved with fewer, thicker disks and with disk thickness increasing toward the target center. The total thickness of Mo100 in the target remaining the same, that reduces the number of coolant gaps. This allows for the gap width to be increased, increasing the mass flow in each gap and consequently increasing heat transfer. A preliminary geometry was selected and analyzed with variable disk thickness and wider coolant gaps. The result of analysis of this target shows that disk thickness increase near the window was too aggressive and further resizing of the disks is necessary, but it does illustrate the potential improvements that are possible. Experimental and analytical study of diffusers on the target exit has been done. This shows modest improvement in requcing pressure drop, as will be summarized below. However, the benefit is not significant, and implementation becomes problematic when disk thickness is varying. A bull nose at the entrance does offer significant benefit and is relatively easy to incorporate. A bull nose on both ends is now a feature of the baseline design, and will be a feature of any redesign or enhanced designs that

  11. Deep absorption band in Cu(In,Ga)Se{sub 2} thin films and solar cells observed by transparent piezoelectric photothermal spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Shirakata, Sho; Atarashi, Akiko [Faculty of Engineering, Ehime University, Matsuyama 790-8577 (Japan); Yagi, Masakazu [Kagawa National College of Technology, Mitoyo-shi 769-1192 (Japan)

    2015-06-15

    The photo-acoustic spectroscopy (PAS) using a transparent piezoelectric photo-thermal (Tr-PPT) method was carried out on Cu(In,Ga)Se{sub 2} (CIGS) thin films (both CIGS/Mo/SLG and CdS/CIGS/Mo/SLG) and solar cells (ZnO/CdS/CIGS/Mo/SLG). Using the Tr-PPT method, the high background absorption in the below gap region observed in both a microphone and a conventional transducer PAS spectra was strongly reduced. This high background absorption came from the CIGS/Mo interface. This result proves that the Tr-PPT PAS is the surface sensitive method. In the below-band region, a bell-shape deep absorption band has been observed at 0.76 eV, in which a full-width at the half-maximum value was 70-120 meV. This deep absorption band was observed for both CdS/CIGS/Mo/SLG and ZnO/CdS/CIGS/Mo/SLG structures. The peak energy of the absorption band was independent of the alloy composition for 0.25≤Ga/III≤0.58. Intensity of the PA signal was negatively correlated to the Na concentration at the CIGS film surface. The origin of the 0.76 eV peak is discussed with relation to native defects such as a Cu-vacancy-related defect (copyright 2015 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  12. Acute nonlymphocytic leukemia in adults: correlations with Q-banded chromosomes

    Energy Technology Data Exchange (ETDEWEB)

    Golomb, H.M.; Vardiman, J.; Rowley, J.D.

    1976-07-01

    Chromosome banding patterns were obtained for 50 of 55 consecutive adult patients with acute nonlymphocytic leukemia during a 5-yr period. Twenty-two of the 50 cases were diagnosed as acute myelocytic leukemia (AML), 24 as acute myelomonocytic leukemia (AMMol), 2 as acute promyelocytic leukemia (APL), and 2 as erythroleukemia. Twenty-five patients had initial chromosome abnormalities, and five more patients developed abnormalities during the course of the disease. The median survival of patients with normal chromosomes initially (group 1) was 10 mo, whereas that of patients with abnormal chromosomes initially (group II) was 2 mo. Similar times were obtained for treated patients with AML and AMMol. However, when the AML patients were separated into those with and those without a chromosome abnormality, the median survival times were markedly different (2 mo versus 18 mo, respectively). Patients with AMMol demonstrated no difference in median survival times when subgrouped according to the presence or absence of chromosome abnormalities. The treated group II patients whose marrow samples had only abnormal metaphases had a poorer response (10 percent complete remission) and median survival (2 mo) than the group II patients who had at least one normal metaphase (42 percent complete remission with a median survival of 9 mo). The two cases of APL demonstrated a deletion of the long arm of No. 17 which occurred in the same region of the chromosome in each case. Both patients had similar clinical histories, with disseminated intravascular coagulation, and neither responded to therapy.

  13. Nd掺杂对δ-MoN电子结构和输运性质的影响%The Nd-doping effect on the electronic structure and the transport property of δ-MoN

    Institute of Scientific and Technical Information of China (English)

    尉靖; 王可答; 金凤友; 刘利军; 张桂玲; 曾涛

    2012-01-01

    To investigate the mechanism of the rare earth element doping effect on the conductivity of materials, the electronic structures and the transport properties of the Nd-doped δ-MoN were theoretically studied by the combination of non-equilibrium Green's function technique with density functional theory. The Mo atoms at 2a and 6c in the Wyckoff positions were substituted, respectively, by the Nd atom for investigating the doping effect on the conductivity of δ-MoN. The band structures, the density of states and the current-voltage curves of the Nd-doped δ-MoN were calculated and analyzed. The calculated electronic structures indicate that the Nd-doping results in the enhancement of the density of states near the Fermi level, which is beneficial to the increase of the carrier density. The current-voltage curves show that the Nd-doped systems possess higher conductivity than the undoped system, implying that the conductivity of δ-MoN is improved upon the Nd-doping. The Nd-doped δ-MoN exhibits higher conductivity when the dopant Nd sits in the 6c position.%为了探讨稀土掺杂对材料导电性影响的机理,采用密度泛函理论并结合非平衡格林函数方法,从理论角度研究了Nd掺杂δ-MoN的电子结构与输运性质,分别讨论了Nd取代Wyckoff坐标系中2a位置和6c位置的Mo原子时对δ-MoN导电性的影响.计算并分析了Nd掺杂δ-MoN的能带结构、态密度和伏安特性曲线.电子结构的计算结果表明,Nd掺杂使δ-MoN在费米能级附近的态密度增大,导致费米面电子出现的几率增加;伏安特性曲线显示Nd掺杂体系的电流大于未掺杂体系,说明Nd掺杂增强了δ-MoN的导电性,其中当Nd取代6c位置的Mo原子时δ-MoN的导电性增强较大.

  14. Surface, optical characteristics and photocatalytic ability of Scheelite-type monoclinic Bi3FeMo2O12 nanoparticles

    Science.gov (United States)

    Nie, Xinming; Wulayin, Wumitijiang; Song, Tingting; Wu, Minxiao; Qiao, Xuebin

    2016-11-01

    Bi3FeMo2O12 nanoparticles with the Scheelite-type monoclinic structure were prepared by the Pechini synthesis. The Bi3FeMo2O12 nanoparticle has a size of about 50 nm. The phase formation and structural characteristic were studied by X-ray diffraction (XRD) patterns and Rietveld refinements. The Scheelite framework is characterized by a superstructure constructed by the ordered arrangement of Fe/Mo tetrahedral on the B sites. The surface characteristics of Bi3FeMo2O12 nanoparticles were studied by the measurements such as the scanning electron microscope (SEM), the transmission electron microscopy (TEM), and the N2-adsorption-desorption isotherm. Bi3FeMo2O12 nanoparticles present an efficient optical absorption in a wide wavelength region from UV to 540 nm. The band gap energy was decided to be 2.3 eV and characterized by a direct allowed electronic optical transition. The photocatalytic activity of Bi3FeMo2O12 nanoparticles was confirmed by the photodegradation of the rhodamine B (RhB) dye solution. The experiments indicate that the Scheelite-type molybdate could be a potential candidate of a visible-light-driven photocatalyst.

  15. Structure and Electronic Properties of In Situ Synthesized Single-Layer MoS2 on a Gold Surface

    DEFF Research Database (Denmark)

    Sørensen, Signe Grønborg; Füchtbauer, Henrik Gøbel; Tuxen, Anders Kyrme

    2014-01-01

    with scanning tunneling microscopy and X-ray photoelectron spectroscopy characterization of two-dimensional single-layer islands of MoS2 synthesized directly on a gold single crystal substrate. Thanks to a periodic modulation of the atom stacking induced by the lattice mismatch, we observe a structural buckling...... of the MoS2 layer resulting in a characteristic moiré pattern. X-ray photoelectron spectroscopy indicates that the system develops the characteristics of n-doped MoS2 due to electron donation. Scanning tunneling spectroscopy furthermore reflects a convolution of MoS2 and Au donor states where the MoS2 band......When transition metal sulfides such as MoS2 are present in the single-layer form, the electronic properties change in fundamental ways, enabling them to be used, e.g., in two-dimensional semiconductor electronics, optoelectronics, and light harvesting. The change is related to a subtle modification...

  16. Monolayer MoS2-Graphene Hybrid Aerogels with Controllable Porosity for Lithium-Ion Batteries with High Reversible Capacity.

    Science.gov (United States)

    Jiang, Lianfu; Lin, Binghui; Li, Xiaoming; Song, Xiufeng; Xia, Hui; Li, Liang; Zeng, Haibo

    2016-02-03

    Monolayer MoS2 nanosheets (NSs) are promising anode materials for lithium-ion batteries because all redox reactions take place at the surface without lithium-ion diffusion limit. However, the expanded band gap of monolayer MoS2 NSs (∼1.8 eV) compared to their bulk counterparts (∼1.2 eV) and restacking tendency due to the van der Waals forces result in poor electron transfer and loss of the structure advantage. Here, a facile approach is developed to fabricate the MoS2-graphene aerogels comprising controlled three-dimensional (3D) porous architectures constructed by interconnected monolayer MoS2-graphene hybrid NSs. The robust 3D architectures combining with the monolayer feature of the hybrid NSs not only prevent the MoS2 and graphene NSs from restacking, but also enable fast electrode kinetics due to the surface reaction mechanism and highly conductive graphene matrix. As a consequence, the 3D porous monolayer MoS2-graphene composite aerogels exhibit a large reversible capacity up to 1200 mAh g(-1) as well as outstanding cycling stability and rate performance, making them promising as advanced anode materials for lithium-ion batteries.

  17. Synthesis of MoSi2 by Mechanical Alloying

    Institute of Scientific and Technical Information of China (English)

    2001-01-01

    The microstructure evolution of mechanical alloyed Mo-66.7%Si powder using the high-energy ball mill has been studied by X-ray diffraction and scanning electron microscopy. The results showed that MoSi2 can be synthesized by MA of Mo-66.7%Si powder mixtures. Cold welding behavior between Mo and Si powders plays an important role in the preparation of MoSi2 by the MA.

  18. Stability of defects in monolayer MoS2 and their interaction with O2 molecule: A first-principles study

    Science.gov (United States)

    Zhao, B.; Shang, C.; Qi, N.; Chen, Z. Y.; Chen, Z. Q.

    2017-08-01

    The stability of various defects in monolayer MoS2, as well as their interactions with free O2 molecules were investigated by density functional theory (DFT) calculations coupled with the nudged elastic band (NEB) method. The defects including S vacancy (monosulfur and disulfue vacancies), antisite defect (MoS) and external Mo atom can exist steadily in monolayer MoS2, and introduce defect levels in these defective systems, which breaks the surface chemical inertness and significantly enhances the adsorption capacity for free O2. The adsorption energy calculations and electronic properties analysis suggest that there is a strong interaction between O2 molecule and defective system. The adsorbed O2 on the defective surface can dissociate with a lower activation energy barrier, which produce two active oxygen atoms. Especially, two Mo atoms can occupy one Mo lattice site, and adsorbed O2 on the top of the Mo atom can then dissociate directly with the lowest activation energy barrier. Hence, our work may provide useful information to design MoS2-based gas sensor or catalysts.

  19. Visible-light-induced blue MoO{sub 3}–C{sub 3}N{sub 4} composite with enhanced photocatalytic activity

    Energy Technology Data Exchange (ETDEWEB)

    Li, Yeping, E-mail: ypli@ujs.edu.cn [School of Pharmacy, Jiangsu University, Zhenjiang 212013 (China); Huang, Liying [School of Chemistry and Chemical Engineering, Jiangsu University, Zhenjiang 212013 (China); Xu, Jingbo [School of Pharmacy, Jiangsu University, Zhenjiang 212013 (China); Xu, Hui [Institute for Energy Research, Jiangsu University, Zhenjiang 212013 (China); Xu, Yuanguo; Xia, Jixiang [School of Chemistry and Chemical Engineering, Jiangsu University, Zhenjiang 212013 (China); Li, Huaming, E-mail: lihm@ujs.edu.cn [Institute for Energy Research, Jiangsu University, Zhenjiang 212013 (China)

    2015-10-15

    Highlights: • Novel MoO{sub 3}–C{sub 3}N{sub 4} composite was prepared by a mixing-calcination method. • The MoO{sub 3}–C{sub 3}N{sub 4} composite shows remarkably enhanced absorption of visible light. • The MoO{sub 3}–C{sub 3}N{sub 4} composite shows superior visible-light photocatalytic activity. - Abstract: Composite photocatalyst of blue MoO{sub 3}/g-C{sub 3}N{sub 4} (denoted as MoO{sub 3}–C{sub 3}N{sub 4}) was prepared by a simple mixing-calcination method. The obtained MoO{sub 3}–C{sub 3}N{sub 4} composite contains a low amount of molybdenum blue and shows remarkably enhanced absorption of visible light and high efficiency for the degradation of methylene blue dye (MB) under visible light. The enhancement of visible light photocatalytic activity in MoO{sub 3}–C{sub 3}N{sub 4} is attributed to the synergetic effect: (i) the strong and wide absorption of visible light, (ii) the high separation and easy transfer of photogenerated electron–hole pairs at the heterojunction interfaces derived from the match of band position between the g-C{sub 3}N{sub 4} and MoO{sub 3}.

  20. Endoscopic band ligation for bleeding lesions in the small bowel

    Institute of Scientific and Technical Information of China (English)

    Takashi; Ikeya; Naoki; Ishii; Yuto; Shimamura; Kaoru; Nakano; Mai; Ego; Kenji; Nakamura; Koichi; Takagi; Katsuyuki; Fukuda; Yoshiyuki; Fujita

    2014-01-01

    AIM: To investigate the safety and efficacy of endo-scopic band ligation(EBL) for bleeding lesions in the small bowel.METHODS: This is a retrospective study evaluating EBL in six consecutive patients(three males, three fe-males, 46-86 years of age) treated between May 2009 and February 2014: duodenal vascular ectasia; 1, je-junal bleeding diverticulum; 1, ileal Dieulafoy’s lesion; 1 and ileal bleeding diverticula; 3. The success of the initial hemostasis was evaluated, and patients were observed for early rebleeding(within 30 d after EBL), and complications such as perforation and abscess for-mation. Follow-up endoscopies were performed in four patients.RESULTS: Initial hemostasis was successfully achieved with EBL in all six patients. Eversion was not sufficient in four diverticular lesions. Early rebleeding occurred three days after EBL in one ileal diverticulum, and arepeat endoscopy revealed dislodgement of the O-band and ulcer formation at the banded site. This rebleeding was managed conservatively. Late rebleeding occurred in this case(13 and 21 mo after initial EBL), and re-EBL was performed. Follow-up endoscopies revealed scar formation and the disappearance of vascular lesions at the banded site in the case with a duodenal bleeding lesion, and unresolved ileal diverticula in three cases. Surgery or transarterial embolization was not required without any complications during the median follow-up period of 45(range, 2-83) mo.CONCLUSION: EBL is a safe and effective endoscopic treatment for hemostasis of bleeding lesions in the small bowel.

  1. Impact of reduced graphene oxide on MoS{sub 2} grown by sulfurization of sputtered MoO{sub 3} and Mo precursor films

    Energy Technology Data Exchange (ETDEWEB)

    Pacley, Shanee, E-mail: shanee.pacley@us.af.mil; Brausch, Jacob; Beck-Millerton, Emory [U.S. Air Force Research Laboratory (AFRL)/Wright Patterson Air Force Base, Wright Patterson, Ohio 45433-7707 (United States); Hu, Jianjun; Jespersen, Michael [University of Dayton Research Institute, 300 College Park, Dayton, Ohio 45469 (United States); Hilton, Al [Wyle Laboratories, 4200 Colonel Glenn Hwy, Beavercreek, Ohio 45431 (United States); Waite, Adam [University Technology Corporation, 1270 N Fairfield Rd., Beavercreek, Ohio 45432 (United States); Voevodin, Andrey A. [Department of Materials Science and Engineering, University of North Texas, 1155 Union Circle, Denton, Texas 76203 (United States)

    2016-07-15

    Monolayer molybdenum disulfide (MoS{sub 2}), a two dimensional semiconducting dichalcogenide material with a bandgap of 1.8–1.9 eV, has demonstrated promise for future use in field effect transistors and optoelectronics. Various approaches have been used for MoS{sub 2} processing, the most common being chemical vapor deposition. During chemical vapor deposition, precursors such as Mo, MoO{sub 3}, and MoCl{sub 5} have been used to form a vapor reaction with sulfur, resulting in thin films of MoS{sub 2}. Currently, MoO{sub 3} ribbons and powder, and MoCl{sub 5} powder have been used. However, the use of ribbons and powder makes it difficult to grow large area-continuous films. Sputtering of Mo is an approach that has demonstrated continuous MoS{sub 2} film growth. In this paper, the authors compare the structural properties of MoS{sub 2} grown by sulfurization of pulse vapor deposited MoO{sub 3} and Mo precursor films. In addition, they have studied the effects that reduced graphene oxide (rGO) has on MoS{sub 2} structure. Reports show that rGO increases MoS{sub 2} grain growth during powder vaporization. Herein, the authors report a grain size increase for MoS{sub 2} when rGO was used during sulfurization of both sputtered Mo and MoO{sub 3} precursors. In addition, our transmission electron microscopy results show a more uniform and continuous film growth for the MoS{sub 2} films produced from Mo when compared to the films produced from MoO{sub 3}. Atomic force microscopy images further confirm this uniform and continuous film growth when Mo precursor was used. Finally, x-ray photoelectron spectroscopy results show that the MoS{sub 2} films produced using both precursors were stoichiometric and had about 7–8 layers in thickness, and that there was a slight improvement in stoichiometry when rGO was used.

  2. MoTe2 : A Type-II Weyl Topological Metal

    Science.gov (United States)

    Wang, Zhijun; Gresch, Dominik; Soluyanov, Alexey A.; Xie, Weiwei; Kushwaha, S.; Dai, Xi; Troyer, Matthias; Cava, Robert J.; Bernevig, B. Andrei

    2016-07-01

    Based on the ab initio calculations, we show that MoTe2 , in its low-temperature orthorhombic structure characterized by an x-ray diffraction study at 100 K, realizes 4 type-II Weyl points between the N th and (N +1 )th bands, where N is the total number of valence electrons per unit cell. Other WPs and nodal lines between different other bands also appear close to the Fermi level due to a complex topological band structure. We predict a series of strain-driven topological phase transitions in this compound, opening a wide range of possible experimental realizations of different topological semimetal phases. Crucially, with no strain, the number of observable surface Fermi arcs in this material is 2—the smallest number of arcs consistent with time-reversal symmetry.

  3. Band gap modulation of transition-metal dichalcogenide MX2 nanosheets by in-plane strain

    Science.gov (United States)

    Su, Xiangying; Ju, Weiwei; Zhang, Ruizhi; Guo, Chongfeng; Yong, Yongliang; Cui, Hongling; Li, Xiaohong

    2016-10-01

    The electronic properties of quasi-two-dimensional honeycomb structures of MX2 nanosheets (M=Mo, W and X=S, Se) subjected to in-plane biaxial strain have been investigated using first-principles calculations. We demonstrate that the band gap of MX2 nanosheets can be widely tuned by applying tensile or compressive strain, and these ultrathin materials undergo a universal reversible semiconductor-metal transition at a critical strain. Compared to WX2, MoX2 need a smaller critical tensile strain for the band gap close, and MSe2 need a smaller critical compressive strain than MS2. Taking bilayer MoS2 as an example, the variation of the band structures was studied and the semiconductor-metal transition involves a slightly different physical mechanism between tensile and compressive strain. The ability to tune the band gap of MX2 nanosheets in a controlled fashion over a wide range of energy opens up the possibility for its usage in a range of application.

  4. Pulsed cathodoluminescence and Raman spectra of MoS{sub 2} and WS{sub 2} nanocrystals and their combination MoS{sub 2}/WS{sub 2} produced by self-propagating high-temperature synthesis

    Energy Technology Data Exchange (ETDEWEB)

    Bozheyev, Farabi, E-mail: farabi.bozheyev@gmail.com [Institute of High Technology Physics, National Research Tomsk Polytechnic University, 30 Lenin Ave., 634050 Tomsk (Russian Federation); National Nanolaboratory, al-Farabi Kazakh National University, 71 al-Farabi Ave., 050000 Almaty (Kazakhstan); Nazarbayev University Research and Innovation System, 53 Kabanbay Batyr St., 010000 Astana (Kazakhstan); Valiev, Damir [Institute of High Technology Physics, National Research Tomsk Polytechnic University, 30 Lenin Ave., 634050 Tomsk (Russian Federation); Nemkayeva, Renata [National Nanolaboratory, al-Farabi Kazakh National University, 71 al-Farabi Ave., 050000 Almaty (Kazakhstan)

    2016-02-29

    Molybdenum and tungsten disulfide nanoplates were produced by self-propagating high-temperature synthesis in argon atmosphere. This method provides an easy way to produce MoS{sub 2} and WS{sub 2} from nanoplates up to single- and several layers. The Raman peak intensities corresponding to in-plane E{sup 1}{sub 2g} and out-of-plane A{sub 1g} vibration modes and their shifts strongly depend on the thicknesses of the MoS{sub 2} and WS{sub 2} platelets indicating size-dependent scaling laws and properties. An electron beam irradiation of MoS{sub 2} and WS{sub 2} powders leads to an occurrence of pulsed cathodoluminescence (PCL) spectra at 575 nm (2.15 eV) and 550 nm (2.25 eV) characteristic to their intrinsic band gaps. For the combination of MoS{sub 2} and WS{sub 2} nanopowders, a PCL shoulder at 430 nm (2.88 eV) was observed, which is explained by the radiative electron-hole recombination at the MoS{sub 2}/WS{sub 2} grain boundaries. The luminescence decay kinetics of the MoS{sub 2}/WS{sub 2} nanoplates appears to be slower than for individual MoS{sub 2} and WS{sub 2} platelets due to a spatial separation of electrons and holes at MoS{sub 2}/WS{sub 2} junction resulting in extension of recombination time.

  5. Growth of centimeter-scale atomically thin MoS2 films by pulsed laser deposition

    Directory of Open Access Journals (Sweden)

    Gene Siegel

    2015-05-01

    Full Text Available We are reporting the growth of single layer and few-layer MoS2 films on single crystal sapphire substrates using a pulsed-laser deposition technique. A pulsed KrF excimer laser (wavelength: 248 nm; pulse width: 25 ns was used to ablate a polycrystalline MoS2 target. The material thus ablated was deposited on a single crystal sapphire (0001 substrate kept at 700 °C in an ambient vacuum of 10−6 Torr. Detailed characterization of the films was performed using atomic force microscopy (AFM, Raman spectroscopy, UV-Vis spectroscopy, and photoluminescence (PL measurements. The ablation of the MoS2 target by 50 laser pulses (energy density: 1.5 J/cm2 was found to result in the formation of a monolayer of MoS2 as shown by AFM results. In the Raman spectrum, A1g and E12g peaks were observed at 404.6 cm−1 and 384.5 cm−1 with a spacing of 20.1 cm−1, confirming the monolayer thickness of the film. The UV-Vis absorption spectrum exhibited two exciton absorption bands at 672 nm (1.85 eV and 615 nm (2.02 eV, with an energy split of 0.17 eV, which is in excellent agreement with the theoretically predicted value of 0.15 eV. The monolayer MoS2 exhibited a PL peak at 1.85 eV confirming the direct nature of the band-gap. By varying the number of laser pulses, bi-layer, tri-layer, and few-layer MoS2 films were prepared. It was found that as the number of monolayers (n in the MoS2 films increases, the spacing between the A1g and E12g Raman peaks (Δf increases following an empirical relation, Δ f = 26 . 45 − 15 . 42 1 + 1 . 44 n 0 . 9 cm − 1 .

  6. Production of 99Mo Using 33 MeV Electron and 100Mo Target

    Institute of Scientific and Technical Information of China (English)

    LIU; Bao-jie; LI; Jin-hai; ZENG; Zi-qiang

    2015-01-01

    The(γ,n)reaction on a 100Mo target is considered to produce the radioactive isotope 100Mo.The advantages of this reaction are the relatively high reaction cross section and the elimination of the expensive fission products chemistry steam associated with irradiation of uranium.The rela-

  7. EFFECT OF CONCENTRATION METAL PRECURSOR Co AND Mo ON CHARACTER OF CoMo / USY CATALYST

    Directory of Open Access Journals (Sweden)

    Khoirina Dwi Nugrahaningtyas

    2016-08-01

    Full Text Available The preparation and characterization of bimetallic catalysts using impregnation method with a variation of concentration of precursor sequence Co and Mo metal obtained catalyst K 1 [Co (0.018 M - Mo (0.037 M/USY]. K 2 [Co (0.026 M - Mo (0.055 M/USY], K 3 [Co (0.035 M - Mo (0.074 M/USY], K 4 [Co (0.05 M - Mo (0.11 M /USY] and K 5 [Co (0.107 M - Mo (0.22 M/USY]. Character of the catalyst in terms of crystallinity was analyzed by XRD. The result shows that there is no cristalinity damage of USY after impregnation but the amorphous cristalin structure was obtained. Amount of metal content was analyzed by XRF and the catalyst morphology by SEM-EDS. The result shows that the higher the concentration of Co and Mo so that find the higher content of metal in catalyst of the prepared catalyst increase. K 4 shows the best characteristic of catalysts prepared in this research. Analysis of K 4 is proving that Co and Mo are presented in catalyst.

  8. Cluster banding heat source model

    Institute of Scientific and Technical Information of China (English)

    Zhang Liguo; Ji Shude; Yang Jianguo; Fang Hongyuan; Li Yafan

    2006-01-01

    Concept of cluster banding heat source model is put forward for the problem of overmany increment steps in the process of numerical simulation of large welding structures, and expression of cluster banding heat source model is deduced based on energy conservation law.Because the expression of cluster banding heat source model deduced is suitable for random weld width, quantitative analysis of welding stress field for large welding structures which have regular welds can be made quickly.

  9. Theoretical Simulation for Identical Bands

    Institute of Scientific and Technical Information of China (English)

    CHEN Yong-Jing; CHEN Yong-Shou; GAO Zao-Chun

    2004-01-01

    @@ The frequency of occurrence of identical bands is studied by analysing a large number of rotational bands calculated with the reflection asymmetric shell model, and the statistical properties of identical bands indicated in all the experimental observations are reproduced within the mean field approximation and beyond mean field treatment, such as angular momentum projection. The distributions of the calculated J(2), Eγ and the fractional change of J(2) are discussed.

  10. Photovoltaic heterojunctions of fullerenes with MoS2 and WS 2 monolayers

    KAUST Repository

    Gan, Liyong

    2014-04-17

    First-principles calculations are performed to explore the geometry, bonding, and electronic structures of six ultrathin photovoltaic heterostructures consisting of pristine and B- or N-doped fullerenes and MoS2 or WS2 monolayers. The fullerenes prefer to be attached with a hexagon parallel to the monolayer, where B and N favor proximity to the monolayer. The main electronic properties of the subsystems stay intact, suggesting weak interfacial interaction. Both the C60/MoS 2 and C60/WS2 systems show type-II band alignments. However, the built-in potential in the former case is too small to effectively drive electron-hole separation across the interface, whereas the latter system is predicted to show good photovoltaic performance. Unfortunately, B and N doping destroys the type-II band alignment on MoS2 and preserves it only in one spin channel on WS2, which is unsuitable for excitonic solar cells. Our results suggest that the C60/WS 2 system is highly promising for excitonic solar cells. © 2014 American Chemical Society.

  11. A new approach to increase the Curie temperature of Fe-Mo double perovskites

    Energy Technology Data Exchange (ETDEWEB)

    Rubi, D. [Institut de Ciencia de Materials de Barcelona, Campus UAB, E-08193, Bellaterra (Spain); Frontera, C. [Institut de Ciencia de Materials de Barcelona, Campus UAB, E-08193, Bellaterra (Spain); Roig, A. [Institut de Ciencia de Materials de Barcelona, Campus UAB, E-08193, Bellaterra (Spain); Nogues, J. [Departament de Fisica, Universitat Autonoma de Barcelona, 08193 Bellaterra, Catalunya (Spain); Institut Catala de Recerca i Estudis Avancats (ICREA), 08193 Bellaterra, Catalunya (Spain); Munoz, J.S. [Departament de Fisica, Universitat Autonoma de Barcelona, 08193 Bellaterra, Catalunya (Spain); Fontcuberta, J. [Institut de Ciencia de Materials de Barcelona, Campus UAB, E-08193, Bellaterra (Spain)]. E-mail: fontcuberta@icmab.es

    2006-01-25

    Sr{sub 2}FeMoO{sub 6} and related double perovskites are nowadays intensely investigated due to their potential in the field of spintronics. It has been previously shown that the Curie temperature (T {sub C}) of double perovskites can be increased by injecting carriers in the conduction band. We report here on an alternative approach to reinforce the magnetic interaction, and thus raise T {sub C}. It can be suspected that the introduction of Fe excess in the Fe-Mo sub-lattice, which would lead into the appearance of nearest neighbour Fe-O-Fe antiferromagnetic spin coupling, could reinforce the next-near neighbour Fe-O-Fe-O-Fe ferromagnetic ordering and thus raise the Curie temperature. The plausibility of this mechanism was checked, in the first place, by means of Monte Carlo simulations. Afterwards, Nd{sub 2x}Ca{sub 2-2x}Fe{sub 1+x}Mo{sub 1-x}O{sub 6} series was prepared and fully characterized, being found that the Curie temperature rises as much as {delta}T {sub C} {approx} 75 K when the Fe content is increased. We argue that this is a genuine magnetic exchange effect, not related neither to steric distortions nor band filling.

  12. Peculiar half-metallic state in zigzag nanoribbons of MoS2: Spin filtering

    Science.gov (United States)

    Khoeini, F.; Shakouri, Kh.; Peeters, F. M.

    2016-09-01

    Layered structures of molybdenum disulfide (MoS2) belong to a new class of two-dimensional (2D) semiconductor materials in which monolayers exhibit a direct band gap in their electronic spectrum. This band gap has recently been shown to vanish due to the presence of metallic edge modes when MoS2 monolayers are terminated by zigzag edges on both sides. Here, we demonstrate that a zigzag nanoribbon of MoS2, when exposed to an external exchange field in combination with a transverse electric field, has the potential to exhibit a peculiar half-metallic nature and thereby allows electrons of only one spin direction to move. The peculiarity of such spin-selective conductors originates from a spin switch near the gap-closing region, so the allowed spin orientation can be controlled by means of an external gate voltage. It is shown that the induced half-metallic phase is resistant to random fluctuations of the exchange field as well as the presence of edge vacancies.

  13. Structural, electronic and adsorption properties of Rh(111)/Mo(110) bimetallic catalyst: A DFT study

    Science.gov (United States)

    Palotás, K.; Bakó, I.; Bugyi, L.

    2016-12-01

    Geometric and electronic characterizations of one monolayer rhodium with Nishiyama-Wassermann (NW) structure on Mo(110) substrate have been performed by density functional theory (DFT) calculations. In the NW structure the Rh atoms form a wavy structure propagating along the [001] direction, characterized by an amplitude of 0.26 Å in the [110] direction and by 0.10 Å in the [110] direction of the Mo(110) substrate. Strain and ligand effects operating in the rhodium film are distinguished and found to be manifested in the downward shift of the d-band center of the electron density of states (DOS) by 0.11 eV and 0.18 eV, respectively. The shift in the d-band center of Rh DOS predicts a decrease in the surface reactivity toward CO adsorption, which has been verified by detailed calculations of bond energies of CO located at on-top, bridge and hollow adsorption sites. The CO adsorption energies are decreased by about 35% compared to those reported for pure Rh(111), offering novel catalytic pathways for the molecule. An in-depth analysis of the charge transfer and the partial DOS characters upon CO adsorption on the NW-structured Rh(111)/Mo(110) bimetallic catalyst and on the pure Rh(111) surface sheds light on the bonding mechanism of CO and on the governing factors determining its lowered bond energy on the bimetallic surface.

  14. Photovoltaic Heterojunctions of Fullerenes with MoS2 and WS2 Monolayers.

    Science.gov (United States)

    Gan, Li-Yong; Zhang, Qingyun; Cheng, Yingchun; Schwingenschlögl, Udo

    2014-04-17

    First-principles calculations are performed to explore the geometry, bonding, and electronic structures of six ultrathin photovoltaic heterostructures consisting of pristine and B- or N-doped fullerenes and MoS2 or WS2 monolayers. The fullerenes prefer to be attached with a hexagon parallel to the monolayer, where B and N favor proximity to the monolayer. The main electronic properties of the subsystems stay intact, suggesting weak interfacial interaction. Both the C60/MoS2 and C60/WS2 systems show type-II band alignments. However, the built-in potential in the former case is too small to effectively drive electron-hole separation across the interface, whereas the latter system is predicted to show good photovoltaic performance. Unfortunately, B and N doping destroys the type-II band alignment on MoS2 and preserves it only in one spin channel on WS2, which is unsuitable for excitonic solar cells. Our results suggest that the C60/WS2 system is highly promising for excitonic solar cells.

  15. Study of tribological behavior of Cu–MoS2 and Ag–MoS2 nanocomposite lubricants

    OpenAIRE

    An, V.; Anisimov, E.; Druzyanova, V.; Burtsev, N.; Shulepov, I.; Khaskelberg, M.

    2016-01-01

    Tribological behavior of Cu–MoS2 and Ag–MoS2 nanocomposite lubricant was studied. Cu nanoparticles produced by electrical explosion of copper wires and Ag nanoparticles prepared by electrospark erosion were employed as metal cladding modifiers of MoS2 nanolamellar particles. The tribological tests showed Cu–MoS2 and Ag–MoS2 nanocomposite lubricants changed the friction coefficient of the initial grease and essentially improved its wear resistance.

  16. States of carbon nanotube supported Mo-based HDS catalysts

    Energy Technology Data Exchange (ETDEWEB)

    Shang, Hongyan; Liu, Chenguang; Xu, Yongqiang [Key Laboratory of Catalysis, CNPC, College of Chemistry and Chemical Engineering, University of Petroleum, Dongying 257061 (China); Qiu, Jieshan [Carbon Research Laboratory, Center for Nano Materials and Science, Dalian University of Technology, 158 Zhongshan Road, P. O. Box 49, Dalian 116012 (China); Wei, Fei [Department of Chemical Engineering, Tsinghua University, Being, 100084 (China)

    2007-02-15

    As HDS catalysts, the supported catalysts including oxide state Mo, Co-Mo and sulfide state Mo on carbon nanotube (CNT) were prepared, while the corresponding supported catalysts on {gamma}-Al{sub 2}O{sub 3} were prepared as comparison. Firstly, the dispersion of the active phase and loading capacity of Mo species on CNT was studied by XRD and the reducibility properties of Co-Mo catalysts in oxide state over CNTs were investigated by TPR while the sulfide Co-Mo/CNT catalysts were characterized by XRD and LRS techniques. Secondly, the activity and selectivity of hydrodesulfurization (HDS) of dibenzothiophene with Co-Mo/CNT and Co-Mo/{gamma}-Al{sub 2}O{sub 3} were studied. It has been found that the main active molybdenum species in the oxide state MoO{sub 3}/CNT catalysts were MoO{sub 2}, rather than MoO{sub 3} as generally expected. The maximum loading before formation of the bulk phase was lower than 6%m (calculated in MoO{sub 3}). The TPR studies revealed that that active species in oxide state Co-Mo/CNT catalysts were more easily reduced at relatively lower temperatures in comparison to those in Co-Mo/{gamma}-Al{sub 2}O{sub 3}, indicating that the CNT support promoted the reduction of active species. Among 0-1.0 Co/Mo atomic ratio on Co-Mo/CNT, 0.7 has the highest reducibility. It shows that the Co/Mo atomic ratio has a great effect on the reducibility of active species on CNT and their HDS activities and that the incorporation of cobalt improved the dispersion of molybdenum species on CNT and mobilization. It was also found that re-dispersion could occur during the sulfiding process, resulting in low valence state Mo{sub 3}S{sub 4} and Co-MoS{sub 2.17} active phases. The HDS of DBT showed that Co-Mo/CNT catalysts were more active than Co-Mo/{gamma}-Al{sub 2}O{sub 3} and the hydrogenolysis/hydrogenation selectivity of Co-Mo/CNT catalyst was also much higher than Co-Mo/{gamma}-Al{sub 2}O{sub 3}. For the Co-Mo/CNT catalysis system, the catalyst with Co/Mo atomic

  17. Iliotibial band Z-lengthening.

    Science.gov (United States)

    Richards, David P; Alan Barber, F; Troop, Randal L

    2003-03-01

    Iliotibial band friction syndrome (ITBFS) is a common overuse injury reported to afflict 1.6% to 12% of runners. It results from an inflammatory response secondary to excessive friction that occurs between the lateral femoral epicondyle and the iliotibial band. Initial treatments include rest, anti-inflammatory medication, modalities (ice or heat), stretching, physical therapy, and possibly a cortisone injection. In recalcitrant cases of ITBFS, surgery has been advocated. This report describes a surgical technique of Z-lengthening of the iliotibial band in patients presenting with lateral knee pain localized to the iliotibial band at the lateral femoral epicondyle and Gerdy's tubercle who failed all nonoperative efforts.

  18. Scarless platysmaplasty for platysmal bands

    Directory of Open Access Journals (Sweden)

    Shiffman Melvin

    2004-01-01

    Full Text Available Transection of plastysmal bands has required a surgical approach that leaves scars and limits patient activities for a period of time. The author has developed a simple method to transect the platysmal bands under local anesthesia without resorting to skin incisions. The transection is performed with the use of a Vicryl ® suture that is inserted through the skin, around the platysmal band, and then out through the original entry point. A back and forth motion of the suture cuts through the band.

  19. Band calculation of lonsdaleite Ge

    Science.gov (United States)

    Chen, Pin-Shiang; Fan, Sheng-Ting; Lan, Huang-Siang; Liu, Chee Wee

    2017-01-01

    The band structure of Ge in the lonsdaleite phase is calculated using first principles. Lonsdaleite Ge has a direct band gap at the Γ point. For the conduction band, the Γ valley is anisotropic with the low transverse effective mass on the hexagonal plane and the large longitudinal effective mass along the c axis. For the valence band, both heavy-hole and light-hole effective masses are anisotropic at the Γ point. The in-plane electron effective mass also becomes anisotropic under uniaxial tensile strain. The strain response of the heavy-hole mass is opposite to the light hole.

  20. Mo isotopes in OAE 2 black shales

    Science.gov (United States)

    Westermann, Stephane; Vance, Derek; Cameron, Vyllinniskii; Archer, Corey; Robinson, Stuart A.

    2014-05-01

    Sedimentary rocks, especially organic-rich deposits, have the potential to track change in the oxygenation state of the ocean over geological time. Oceanic anoxic events (OAEs) correspond to periods of profound and rapid environmental change, which have led to both the widespread deposition of black shales and the development of widespread anoxia in the ocean. Understanding the variations in redox conditions during these events is of primary importance, since recent observations and modelling have shown that processes invoked to explain the origin of OAEs are being observed today as a consequence of anthropogenic change. Here, we compare redox-sensitive trace metal (RSTM) distributions and molybdenum (Mo) isotope variations during a major Cretaceous OAE (OAE 2, Bonarelli event). Whereas RSTM have the potential to provide insights regarding local depositional conditions and processes in palaeoceanographic systems, Mo-isotope data can, under certain circumstances, provide quantitative estimates of how the global extent of seawater anoxia may have fluctuated in the past. We selected for study a series sections within the western Tethys (La Contessa and Furlo, Italy) and in the northern Atlantic (DSDP site 367, Cape Verde Basin and ODP site 1276, Newfoundland Basin. RSTM contents show similar trends through all the studied sections, characterized by low concentration below and above the OAE interval and higher concentrations within the Bonarelli interval. This suggests rapid variations in the redox conditions, from suboxic to euxinic conditions during OAE 2. The RSTM enrichment factors (EFs) indicate different depositional conditions and palaeoceanographic processes between the Tethys and the North Atlantic. Whereas the North Atlantic sites show evidence of weak watermass restriction associated with the action of a particulate shuttle within the water column, the EFs of the Tethyan sections are characteristic of unrestricted marine systems. Despite local differences in

  1. Synthesis and novel luminescence properties of one-dimension BaMoO{sub 4}:Ln{sup 3+} nanostructures

    Energy Technology Data Exchange (ETDEWEB)

    Wang, Yuping; Li, Mingxia; Pan, Kai; Wang, Guofeng, E-mail: wanggf_w@163.com

    2015-12-15

    Highlights: • String BaMoO{sub 4}:Ln{sup 3+} nanobeans were prepared by a hydrothermal method. • The Decay dynamics were performed to study the photoluminescence of the BaMoO{sub 4}:Eu{sup 3+} nanobeans. • For BaMoO{sub 4}:Er{sup 3+}/Eu{sup 3+}, the {sup 2}P{sub 3/2} → {sup 4}I{sub 11/2} and {sup 2}H{sub 11/2}/{sup 4}S{sub 3/2} → {sup 4}I{sub 15/2} transitions were observed. - Abstract: String BaMoO{sub 4}:Ln{sup 3+} (Ln = Eu, Tb, Er, and Gd) nanobeans were prepared by a hydrothermal method. The samples were characterized by transmission electron microscope, scanning electron microscope, X-ray diffraction, X-ray photoelectron spectroscope, and Raman spectrometer. Under direct excitation in the charge transfer absorption band, concentration quenching phenomenon occurs and decay dynamics were performed to study the photoluminescence of the string BaMoO{sub 4}:Eu{sup 3+} nanobeans. In the emission spectra of BaMoO{sub 4}:Er{sup 3+}/Eu{sup 3+} under 274 nm excitation, the {sup 2}P{sub 3/2} → {sup 4}I{sub 11/2}, {sup 2}H{sub 11/2} → {sup 4}I{sub 15/2}, and {sup 4}S{sub 3/2} → {sup 4}I{sub 15/2} transitions from Er{sup 3+} ions were observed for the first time. In addition, the photoluminescence properties of BaMoO{sub 4}:Tb{sup 3+}/Eu{sup 3+} and BaMoO{sub 4}:Gd{sup 3+}/Eu{sup 3+} were also investigated.

  2. Schottky barrier engineering via adsorbing gases at the sulfur vacancies in the metal-MoS2 interface.

    Science.gov (United States)

    Su, Jie; Feng, Liping; Zhang, Yan; Liu, Zhengtang

    2017-03-10

    Sulfur vacancies (S-vacancies) are common in monolayer MoS2 (mMoS2). Finding an effective way to control rather than abolish the effect of S-vacancies on contact properties is vital for the application of mMoS2. Here, we propose the adsorption of gases to passivate the S-vacancies in Pt-mMoS2 interfaces. Results demonstrate that gases are stably and preferentially adsorbed at S-vacancies. The n-type Schottky barriers of Pt-mMoS2 interfaces are reduced significantly upon the adsorption electron-donor gases, especially Cl2. The n-type transport character of the Pt-mMoS2 interface can be changed to p-type by the adsorption of electron-acceptor gases. As the adsorption concentration increases, both n- and p-type Schottky barriers are further reduced, and the lowest n- and p-type Schottky barriers are 0.36 and 0 eV, respectively. Note that the variations in Schottky barriers are independent of the oxidizing ability of gases but relative to the average number of valence electrons per gas atom. Analysis demonstrates that although gases at S-vacancies cannot cause gap states to vanish, and can even enhance Fermi level pinning, they modulate charge redistribution and the potential step at the interface region. Moreover, with increasing adsorption concentration, the valence band maximum of mMoS2 shows the opposite variation tendency to that of the potential step. Our results suggest that adsorption of gases is an effective way to passivate S-vacancies to modulate the transport properties of Pt-mMoS2 interfaces.

  3. Fabrication of MgFe2O4/MoS2 Heterostructure Nanowires for Photoelectrochemical Catalysis.

    Science.gov (United States)

    Fan, Weiqiang; Li, Meng; Bai, Hongye; Xu, Dongbo; Chen, Chao; Li, Chunfa; Ge, Yilin; Shi, Weidong

    2016-02-16

    A novel one-dimensional MgFe2O4/MoS2 heterostructure has been successfully designed and fabricated. The bare MgFe2O4 was obtained as uniform nanowires through electrospinning, and MoS2 thin film appeared on the surface of MgFe2O4 after further chemical vapor deposition. The structure of the MgFe2O4/MoS2 heterostructure was systematic investigated by X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectrometry (XPS), and Raman spectra. According to electrochemical impedance spectroscopy (EIS) results, the MgFe2O4/MoS2 heterostructure showed a lower charge-transfer resistance compared with bare MgFe2O4, which indicated that the MoS2 played an important role in the enhancement of electron/hole mobility. MgFe2O4/MoS2 heterostructure can efficiently degrade tetracycline (TC), since the superoxide free-radical can be produced by sample under illumination due to the active species trapping and electron spin resonance (ESR) measurement, and the optimal photoelectrochemical degradation rate of TC can be achieved up to 92% (radiation intensity: 47 mW/cm(2), 2 h). Taking account of its unique semiconductor band gap structure, MgFe2O4/MoS2 can also be used as an photoelectrochemical anode for hydrogen production by water splitting, and the hydrogen production rate of MgFe2O4/MoS2 was 5.8 mmol/h·m(2) (radiation intensity: 47 mW/cm(2)), which is about 1.7 times that of MgFe2O4.

  4. Prospects of zero Schottky barrier height in a graphene-inserted MoS{sub 2}-metal interface

    Energy Technology Data Exchange (ETDEWEB)

    Chanana, Anuja; Mahapatra, Santanu [Nano-Scale Device Research Laboratory, Department of Electronic Systems Engineering, Indian Institute of Science (IISc) Bangalore, Bangalore 560012 (India)

    2016-01-07

    A low Schottky barrier height (SBH) at source/drain contact is essential for achieving high drive current in atomic layer MoS{sub 2}-channel-based field effect transistors. Approaches such as choosing metals with appropriate work functions and chemical doping are employed previously to improve the carrier injection from the contact electrodes to the channel and to mitigate the SBH between the MoS{sub 2} and metal. Recent experiments demonstrate significant SBH reduction when graphene layer is inserted between metal slab (Ti and Ni) and MoS{sub 2}. However, the physical or chemical origin of this phenomenon is not yet clearly understood. In this work, density functional theory simulations are performed, employing pseudopotentials with very high basis sets to get insights of the charge transfer between metal and monolayer MoS{sub 2} through the inserted graphene layer. Our atomistic simulations on 16 different interfaces involving five different metals (Ti, Ag, Ru, Au, and Pt) reveal that (i) such a decrease in SBH is not consistent among various metals, rather an increase in SBH is observed in case of Au and Pt; (ii) unlike MoS{sub 2}-metal interface, the projected dispersion of MoS{sub 2} remains preserved in any MoS{sub 2}-graphene-metal system with shift in the bands on the energy axis. (iii) A proper choice of metal (e.g., Ru) may exhibit ohmic nature in a graphene-inserted MoS{sub 2}-metal contact. These understandings would provide a direction in developing high-performance transistors involving heteroatomic layers as contact electrodes.

  5. Schottky barrier engineering via adsorbing gases at the sulfur vacancies in the metal–MoS2 interface

    Science.gov (United States)

    Su, Jie; Feng, Liping; Zhang, Yan; Liu, Zhengtang

    2017-03-01

    Sulfur vacancies (S-vacancies) are common in monolayer MoS2 (mMoS2). Finding an effective way to control rather than abolish the effect of S-vacancies on contact properties is vital for the application of mMoS2. Here, we propose the adsorption of gases to passivate the S-vacancies in Pt–mMoS2 interfaces. Results demonstrate that gases are stably and preferentially adsorbed at S-vacancies. The n-type Schottky barriers of Pt–mMoS2 interfaces are reduced significantly upon the adsorption electron-donor gases, especially Cl2. The n-type transport character of the Pt–mMoS2 interface can be changed to p-type by the adsorption of electron-acceptor gases. As the adsorption concentration increases, both n- and p-type Schottky barriers are further reduced, and the lowest n- and p-type Schottky barriers are 0.36 and 0 eV, respectively. Note that the variations in Schottky barriers are independent of the oxidizing ability of gases but relative to the average number of valence electrons per gas atom. Analysis demonstrates that although gases at S-vacancies cannot cause gap states to vanish, and can even enhance Fermi level pinning, they modulate charge redistribution and the potential step at the interface region. Moreover, with increasing adsorption concentration, the valence band maximum of mMoS2 shows the opposite variation tendency to that of the potential step. Our results suggest that adsorption of gases is an effective way to passivate S-vacancies to modulate the transport properties of Pt–mMoS2 interfaces.

  6. Superconductivity in Potassium-Doped Metallic Polymorphs of MoS2.

    Science.gov (United States)

    Zhang, Renyan; Tsai, I-Ling; Chapman, James; Khestanova, Ekaterina; Waters, John; Grigorieva, Irina V

    2016-01-13

    Superconducting layered transition metal dichalcogenides (TMDs) stand out among other superconductors due to the tunable nature of the superconducting transition, coexistence with other collective electronic excitations (charge density waves), and strong intrinsic spin-orbit coupling. Molybdenum disulfide (MoS2) is the most studied representative of this family of materials, especially since the recent demonstration of the possibility to tune its critical temperature, Tc, by electric-field doping. However, just one of its polymorphs, band-insulator 2H-MoS2, has so far been explored for its potential to host superconductivity. We have investigated the possibility to induce superconductivity in metallic polytypes, 1T- and 1T'-MoS2, by potassium (K) intercalation. We demonstrate that at doping levels significantly higher than that required to induce superconductivity in 2H-MoS2, both 1T and 1T' phases become superconducting with Tc = 2.8 and 4.6 K, respectively. Unusually, K intercalation in this case is responsible both for the structural and superconducting phase transitions. By adding new members to the family of superconducting TMDs, our findings open the way to further manipulate and enhance the electronic properties of these technologically important materials.

  7. Weak Fermi Level Pinning Effect in Schottky Junction of α-MoTe2

    Science.gov (United States)

    Nakaharai, Shu; Yamamoto, Mahito; Ueno, Keiji; Tsukagoshi, Kazuhito

    Difficulty in hole injection from metal contacts to transition metal dichalcogenide (TMDC) semiconductors has been one of the most serious issues in the application of these 2D materials to future nanoelectronics, which is caused by the strong Fermi level pinning effect in the metal/TMDC Schottky junction. In this work, we found that the holes can be injected efficiently from a large work function metal of Pt to α-molybdenum ditelluride (α-MoTe2; 2H-type), a TMDC semiconductor. The Schottky barrier height for holes at the Pt/ α-MoTe2 interface was extracted to be 40 meV by the temperature dependence of back-gate modulated currents under the flat band condition at the junction, while the Schottky barrier for electrons in the junction with a small work function metal of Ti was found to be 50 meV. Considering the difference in the work functions of Pt and Ti, the Fermi level pinning effect in α-MoTe2 was found to be much weaker than that in other TMDC semiconductors such as MoS2. These results open a way to the realization of complementary type circuits in the 2D materials for future low-power consumption electronics. This work was supported by JSPS KAKENHI Grant Numbers 15K06006, 25107004.

  8. Polarimetry of the Superluminous Supernova LSQ14mo: No Evidence for Significant Deviations from Spherical Symmetry

    Science.gov (United States)

    Leloudas, Giorgos; Patat, Ferdinando; Maund, Justyn R.; Hsiao, Eric; Malesani, Daniele; Schulze, Steve; Contreras, Carlos; de Ugarte Postigo, Antonio; Sollerman, Jesper; Stritzinger, Maximilian D.; Taddia, Francesco; Wheeler, J. Craig; Gorosabel, Javier

    2015-12-01

    We present the first polarimetric observations of a Type I superluminous supernova (SLSN). LSQ14mo was observed with VLT/FORS2 at five different epochs in the V band, with the observations starting before maximum light and spanning 26 days in the rest frame (z = 0.256). During this period, we do not detect any statistically significant evolution (\\lt 2σ ) in the Stokes parameters. The average values we obtain, corrected for interstellar polarization in the Galaxy, are Q = -0.01% (±0.15%) and U = -0.50% (±0.14%). This low polarization can be entirely due to interstellar polarization in the SN host galaxy. We conclude that, at least during the period of observations and at the optical depths probed, the photosphere of LSQ14mo does not present significant asymmetries, unlike most lower-luminosity hydrogen-poor SNe Ib/c. Alternatively, it is possible that we may have observed LSQ14mo from a special viewing angle. Supporting spectroscopy and photometry confirm that LSQ14mo is a typical SLSN I. Further studies of the polarization of Type I SLSNe are required to determine whether the low levels of polarization are a characteristic of the entire class and to also study the implications for the proposed explosion models.

  9. Surface defect passivation of MoS2 by sulfur, selenium, and tellurium

    Science.gov (United States)

    Wang, Ying; Qi, Long; Shen, Lei; Wu, Yihong

    2016-04-01

    Few-layer MoS2 field-effect transistors often show an n-type conduction behavior due to the presence of high-density sulfur vacancies. Here, we investigated the possibility of surface defect passivation of MoS2 by sulfur treatment in (NH4)2S solution or coating with an ultrathin layer of selenium or tellurium. It was found that all three elements investigated are able to induce a p-doping effect through suppressing the residual electron concentration by an amount exceeding 0.5 × 1012 cm-2 in few-layer MoS2. Among them, the sulfur-treatment exhibits the most superior thermal stability that survives thermal annealing at temperatures ≥120 °C for at least 10 h. Tellurium exhibits the strongest p-doping effect due to electron trapping by physisorption-induced gap states near the valence band edge. On the other hand, selenium is highly volatile on MoS2; it evaporates and desorbs easily due to Joule heating during electrical measurements in vacuum. The results of first-principles calculations support the experimental observations.

  10. Polarimetry of the superluminous supernova LSQ14mo: no evidence for significant deviations from spherical symmetry

    CERN Document Server

    Leloudas, Giorgos; Maund, Justyn R; Hsiao, Eric; Malesani, Daniele; Schulze, Steve; Contreras, Carlos; Postigo, Antonio de Ugarte; Sollerman, Jesper; Stritzinger, Maximilian D; Taddia, Francesco; Wheeler, J Craig; Gorosabel, Javier

    2015-01-01

    We present the first polarimetric observations of a Type I superluminous supernova (SLSN). LSQ14mo was observed with VLT/FORS2 at 5 different epochs in the V band, observations starting before maximum light and spanning 26 days in the rest-frame (z=0.256). During this period, we do not detect any statistically significant evolution (< 2$\\sigma$) in the Stokes parameters. The average values we obtain, corrected for interstellar polarisation in the Galaxy, are Q = -0.01% ($\\pm$ 0.15%) and U = - 0.50% ($\\pm$ 0.14%). This low polarisation can be entirely due to interstellar polarisation in the SN host galaxy. We conclude that, at least during the period of observations and at the optical depths probed, the photosphere of LSQ14mo does not present significant asymmetries, unlike most lower-luminosity hydrogen-poor SNe Ib/c. Alternatively, it is possible that we may have observed LSQ14mo from a special viewing angle. Supporting spectroscopy and photometry confirm that LSQ14mo is a typical SLSN I. Further studies ...

  11. Temperature dependence of scintillation properties of SrMoO4

    CERN Document Server

    Mikhailik, V B; Kraus, H; Kim, H J; Kapustianyk, V; Panasyuk, M

    2015-01-01

    Studies of the X-ray luminescence and scintillation properties of a SrMoO4 crystal as function of temperature down to T=10 K have been carried out. The luminescence in SrMoO4 is quenched at room temperature, but below T<200 K the crystal exhibits a broad emission band with a maximum at a wavelength of 520 nm. The emission is attributed to the radiative decay of self-trapped excitons and defects acting as traps for the exactions at low temperatures. Such complex character of radiative decay is reflected in the kinetics which contains several components plus a contribution from delayed recombination at low temperatures. The temperature dependence of scintillation light output of SrMoO4 was studied. Comparing with a reference ZnWO4 crystal measured under the same experimental conditions it was found that the light output of SrMoO4 is 15+-5%. It is suggested, therefore, that there is scope for optimisation of strontium molybdate for application as scintillator in cryogenic rare event searches

  12. Tuning the optoelectronic properties of amorphous MoOx films by reactive sputtering

    DEFF Research Database (Denmark)

    Fernandes Cauduro, André Luis; Fabrim, Zacarias Eduardo; Ahmadpour, Mehrad;

    2015-01-01

    In this letter, we report on the effect of oxygen partial pressure and sputtering power on amorphous DC-sputtered MoOx films. We observe abrupt changes in the optoelectronic properties of the reported films by increasing the oxygen partial pressure from 1.00 ? 10?3 mbar to 1.37 ? 10?3 mbar during...... the sputtering process. A strong impact on the electrical conductivity, varying from 1.6 ? 10?5 S/cm to 3.22 S/cm, and on the absorption coefficient in the range of 0.6–3.0 eV is observed for the nearly stoichiometric MoO3.00 and for the sub-stoichiometric MoO2.57 films, respectively, without modifying...... significantly the microstructure of the studied films. The presence of states within the band gap due to the lack of oxygen is the most probable mechanism for generat- ing a change in electrical conductivity as well as optical absorption in DC-sputtered MoOx. The large tuning range of the optoelectronic...

  13. Temperature dependence of scintillation properties of SrMoO{sub 4}

    Energy Technology Data Exchange (ETDEWEB)

    Mikhailik, V.B., E-mail: vmikhai@hotmail.com [Diamond Light Source, Harwell Science Campus, Didcot OX11 0DE (United Kingdom); Elyashevskyi, Yu. [Department of Physics, University of Oxford, Keble Rd., Oxford OX1 3RH (United Kingdom); Scientific-technical and Educational Centre of Low Temperature Studies, I. Franko National University of Lviv, 50 Dragomanova Str., 79005 Lviv (Ukraine); Kraus, H. [Department of Physics, University of Oxford, Keble Rd., Oxford OX1 3RH (United Kingdom); Kim, H.J. [Department of Physics of Kyungpook National University, 1370 Sangyeok-dong, Buk-gu, Daegu 702-701 (Korea, Republic of); Kapustianyk, V.; Panasyuk, M. [Scientific-technical and Educational Centre of Low Temperature Studies, I. Franko National University of Lviv, 50 Dragomanova Str., 79005 Lviv (Ukraine)

    2015-08-21

    Studies of the X-ray luminescence and scintillation properties of a SrMoO{sub 4} crystal as function of temperature down to T=10 K have been carried out. The luminescence in SrMoO{sub 4} is quenched at room temperature, but below T<200 K the crystal exhibits a broad emission band with a maximum at a wavelength of 520 nm. The emission is attributed to the radiative decay of self-trapped excitons and defects acting as traps for the exactions at low temperatures. Such complex character of radiative decay is reflected in the kinetics which contains several components plus a contribution from delayed recombination at low temperatures. The temperature dependence of scintillation light output of SrMoO{sub 4} was studied. Comparing with a reference ZnWO{sub 4} crystal measured under the same experimental conditions it was found that the light output of SrMoO{sub 4} is 15±5%. It is suggested, therefore, that there is scope for optimisation of strontium molybdate for application as scintillator in cryogenic rare event searches.

  14. Enhancement of photovoltaic response in multilayer MoS2 induced by plasma doping.

    Science.gov (United States)

    Wi, Sungjin; Kim, Hyunsoo; Chen, Mikai; Nam, Hongsuk; Guo, L Jay; Meyhofer, Edgar; Liang, Xiaogan

    2014-05-27

    Layered transition-metal dichalcogenides hold promise for making ultrathin-film photovoltaic devices with a combination of excellent photovoltaic performance, superior flexibility, long lifetime, and low manufacturing cost. Engineering the proper band structures of such layered materials is essential to realize such potential. Here, we present a plasma-assisted doping approach for significantly improving the photovoltaic response in multilayer MoS2. In this work, we fabricated and characterized photovoltaic devices with a vertically stacked indium tin oxide electrode/multilayer MoS2/metal electrode structure. Utilizing a plasma-induced p-doping approach, we are able to form p-n junctions in MoS2 layers that facilitate the collection of photogenerated carriers, enhance the photovoltages, and decrease reverse dark currents. Using plasma-assisted doping processes, we have demonstrated MoS2-based photovoltaic devices exhibiting very high short-circuit photocurrent density values up to 20.9 mA/cm(2) and reasonably good power-conversion efficiencies up to 2.8% under AM1.5G illumination, as well as high external quantum efficiencies. We believe that this work provides important scientific insights for leveraging the optoelectronic properties of emerging atomically layered two-dimensional materials for photovoltaic and other optoelectronic applications.

  15. Biodistribution of 99Mo in rats

    Directory of Open Access Journals (Sweden)

    Raphael Sancho Sisley de Souza

    2008-12-01

    Full Text Available The modification of 99Mo standard metabolism in the presence of MDP would alter the dosimetry of this radionuclide in nuclear medicine patients. Therefore, the objective of this work is to evaluate the influence of MDP in the biodistribution of 99Mo. Wistar rats were divided in two groups of six animals, being inoculated respectively 99Molibdate and 99Mo+MDP via plex ocular. The biodistribution study was carried out after 10 and 120 minutes respectively. The organs were counted with a NaI(Tl detector. The uptake values did not present significant differences among the groups. An in vitro study through planar chromatography was carried out to determine the affinity between molybdenum and MDP. The results show that 99Mo has low affinity both to propanone and NaCl-0.9% solution. However, 99Mo in the presence of MDP presented affinity to NaCl-0.9% solution and low affinity to propanone suggesting that 99Mo was bound to MDP under the conditions of the experiment.A modificação do metabolismo padrão do 99Mo em presença de MDP levaria a alterações na dosimetria deste radionuclídeo em pacientes de medicina nuclear. Assim, o objetivo deste trabalho é avaliar a influência do MDP na biodistribuição de 99Mo. Ratos Wistar foram divididos em dois grupos de seis animais, sendo inoculados respectivamente com 99Molibdato e 99Molibdato+MDP via plexo ocular. O estudo de biodistribuição foi realizado após 10 e 120 minutos respectivamente. Os órgãos foram contados com detector NaI(Tl. Os valores de uptake não apresentaram diferenças significativas entre os grupos. Foi realizado um estudo in vitro através de cromatografia planar para determinar a afinidade entre o molibdênio e o MDP. Os resultados mostraram que o molibdênio tem baixa afinidade tanto pela propanona quanto pela solução 0.9% de NaCl. Entretanto, o molibdênio em presença de MDP apresentou afinidade pela solução 0.9% de NaCl e baixa afinidade pela propanona, sugering ter ocorrido

  16. An investigation of the optical properties and water splitting potential of the coloured metallic perovskites Sr{sub 1−x}Ba{sub x}MoO{sub 3}

    Energy Technology Data Exchange (ETDEWEB)

    Hopper, H.A.; Le, J.; Cheng, J. [Chemistry Department, University of Aberdeen, Meston Walk, Aberdeen AB24 3UE (United Kingdom); Weller, T.; Marschall, R. [Institute of Physical Chemistry, Justus-Liebig-University Giessen, 35392 Giessen (Germany); Bloh, J.Z. [DECHEMA Research Institute, Theodor-Heuss-Allee 25, 60486 Frankfurt am Main (Germany); Macphee, D.E.; Folli, A. [Chemistry Department, University of Aberdeen, Meston Walk, Aberdeen AB24 3UE (United Kingdom); Mclaughlin, A.C., E-mail: a.c.mclaughlin@abdn.ac.uk [Chemistry Department, University of Aberdeen, Meston Walk, Aberdeen AB24 3UE (United Kingdom)

    2016-02-15

    The solid solution Sr{sub 1−x}Ba{sub x}MoO{sub 3} (x=0.00, 0.025, 0.050, 0.075, 0.100 and 1.00) has been synthesised. Rietveld refinement of X-ray diffraction data shows that all materials crystallise with cubic (Pm-3m) symmetry and that a miscibility gap exists from x=0.1–1.0. The optical properties of the metallic perovskites Sr{sub 1−x}Ba{sub x}MoO{sub 3} have been investigated by a combination of UV–vis spectroscopy and density functional theory (DFT). Upon increasing x from 0 to 1 in Sr{sub 1−x}Ba{sub x}MoO{sub 3} there is a reduction in the measured band gap from 2.20 eV to 2.07 eV. The measured band gap is attributed to the electronic transition from the Mo 4d t{sub 2g} band to the e{sub g} band. The potential of SrMoO{sub 3} and BaMoO{sub 3} as water-splitting photocatalysts was explored but there was no evidence of hydrogen or oxygen evolution, even with the presence of a Pt co-catalyst. - Graphical abstract: Ultraviolet–visible absorbance spectra (converted from diffuse reflectance spectra) for SrMoO{sub 3} and BaMoO{sub 3}. - Highlights: • The solid solution Sr{sub 1-x}Ba{sub x}MoO{sub 3} has been synthesised. • A miscibility gap exists from x=0.1–1.0 in Sr{sub 1−x}Ba{sub x}MoO{sub 3.} • Upon increasing x from 0 to 1 in Sr{sub 1−x}Ba{sub x}MoO{sub 3} there is a reduction in the measured band gap from 2.20 eV to 2.07 eV. • The potential of SrMoO{sub 3} and BaMoO{sub 3} as water-splitting photocatalysts was explored but there was no evidence of hydrogen or oxygen evolution, even with the presence of a Pt co-catalyst.

  17. Garage Band or GarageBand[R]? Remixing Musical Futures

    Science.gov (United States)

    Vakeva, Lauri

    2010-01-01

    In this paper, I suggest that it is perhaps time to consider the pedagogy of popular music in more extensive terms than conventional rock band practices have to offer. One direction in which this might lead is the expansion of the informal pedagogy based on a "garage band" model to encompass various modes of digital artistry wherever this artistry…

  18. Tunable thermoelectricity in monolayers of MoS2 and other group-VI dichalcogenides 2 and other group-VI dichalcogenides

    KAUST Repository

    Tahir, M

    2014-10-31

    We study the thermoelectric properties of monolayers of MoS2 and other group-VI dichalcogenides under circularly polarized off-resonant light. Analytical expressions are derived for the Berry phase mediated magnetic moment, orbital magnetization, as well as thermal and Nernst conductivities. Tuning of the band gap by off-resonant light enhances the spin splitting in both the valence and conduction bands and, thus, leads to a dramatic improvement of the spin and valley thermoelectric properties.

  19. From 1D chain to 3D network: a new family of inorganic-organic hybrid semiconductors MO3(L)(x) (M = Mo, W; L = organic linker) built on perovskite-like structure modules.

    Science.gov (United States)

    Zhang, Xiao; Hejazi, Mehdi; Thiagarajan, Suraj J; Woerner, William R; Banerjee, Debasis; Emge, Thomas J; Xu, Wenqian; Teat, Simon J; Gong, Qihan; Safari, Ahmad; Yang, Ronggui; Parise, John B; Li, Jing

    2013-11-20

    MO3 (M = Mo, W) or VI-VI binary compounds are important semiconducting oxides that show great promise for a variety of applications. In an effort to tune and enhance their properties in a systematic manner we have applied a designing strategy to deliberately introduce organic linker molecules in these perovskite-like crystal lattices. This approach has led to a wealth of new hybrid structures built on one-dimensional (1D) and two-dimensional (2D) VI-VI modules. The hybrid semiconductors exhibit a number of greatly improved properties and new functionality, including broad band gap tunability, negative thermal expansion, largely reduced thermal conductivity, and significantly enhanced dielectric constant compared to their MO3 parent phases.

  20. Physico-chemical Characterization of Mo-Hβ Zeolite Catalysts

    Institute of Scientific and Technical Information of China (English)

    LIU Sheng-lin; HUANG Sheng-jun; XIN Wen-jie; QIN xin-hua; XIE Su-juan; XU Long-ya

    2004-01-01

    A series of Mo-impregnated Hβ samples, with MoO3 loading in Hβ zeolite in the mass fraction range of 0. 5%-6.0%, were studied by means of XRD and IR in order to characterize their structures. Mo/Hβ samples' crystallinity almost linearly decreases with increasing the amount of MoO3 loaded. The IR spectra and XRD patterns suggest that the progressive destabilization of the Hβ zeolite structure is caused by increasing Mo loading in (MoO3+Hβ zeolite). During the calcination, Al2(MoO4)3 formed from the dealumination of Hβ zeolite, causes the substantially partial breakdown of the zeolite framework when the Mo loading in MoO3 +Hβ is relatively high.

  1. Phase diagrams of Li2MoO4-Na2MoO4 and Na2MoO4-K2MoO4 systems

    Institute of Scientific and Technical Information of China (English)

    DING Yimin; HOU Na; CHEN Nianyi; XIA Yiben

    2006-01-01

    The phase diagrams of the Li2MoO4-Na2MoO4 and Na2MoO4-K2MoO4 systems have been reassessed using differential thermal analysis together with high-temperature and room-temperature X-ray diffraction analysis. The results showed that the compound Li2MoO4·6Na2MoO4 did not exist; however, it confirmed the existence of the compound Li2MoO4·3Na2MoO4 in the Li2MoO4-Na2MoO4 systems. With regard to the system of Na2MoO4-K2MoO4, we could not confirm the results reported by Bukhanova who claimed that the system was eutectic type with 1∶1 and 1∶2 intermediate compounds, refuting the statement of Amadori who thought there was an apparent phase boundary at high temperature in α-solid solution region of the Na2MoO4-K2MoO4 binary system. The revised phase diagrams of these systems are illustrated in this article. These experimental results are in agreement with the computerized prediction using the support vector machine-atomic parameter method for the assessment of phase diagrams.

  2. Recent results from MoNA-LISA

    Science.gov (United States)

    Spyrou, Artemisia

    2012-03-01

    Studies of the nuclear properties of nuclei close and even beyond the limits of stability have revealed exotic modes of decay and new structural characteristics. The MoNA-LISA array is used at the National Superconducting Cyclotron Laboratory at Michigan State University to study nuclei along the neutron dripline. In a typical experiment, a radioactive beam is employed to produce the neutron-unbound state of interest. This state/resonance immediately decay into a neutron, which is detected by MoNA-LISA and a remaining charged nucleus detected by the sweeper magnet detector suite. In this talk, new exciting findings from recent MoNA-LISA experiments will be presented. These include the first observation of a dineutron decay from ^16Be, the exploration of the ``south shore'' of the Island of Inversion and the first evidence of the decay of the troubling nucleus ^26O.

  3. Long Lake banding project, 1965

    Data.gov (United States)

    US Fish and Wildlife Service, Department of the Interior — This report summarizes the results of a banding project on Long Lake in 1965. The dates at the banding site were July 27th through August 8th. As in the past, the...

  4. Enhanced photovoltaic performances of graphene/Si solar cells by insertion of a MoS₂ thin film.

    Science.gov (United States)

    Tsuboi, Yuka; Wang, Feijiu; Kozawa, Daichi; Funahashi, Kazuma; Mouri, Shinichiro; Miyauchi, Yuhei; Takenobu, Taishi; Matsuda, Kazunari

    2015-09-14

    Transition-metal dichalcogenides exhibit great potential as active materials in optoelectronic devices because of their characteristic band structure. Here, we demonstrated that the photovoltaic performances of graphene/Si Schottky junction solar cells were significantly improved by inserting a chemical vapor deposition (CVD)-grown, large MoS2 thin-film layer. This layer functions as an effective electron-blocking/hole-transporting layer. We also demonstrated that the photovoltaic properties are enhanced with the increasing number of graphene layers and the decreasing thickness of the MoS2 layer. A high photovoltaic conversion efficiency of 11.1% was achieved with the optimized trilayer-graphene/MoS2/n-Si solar cell.

  5. Thin film growth and Zn doping of h-MoO3 hexagonal rods by hydrothermal technique

    Science.gov (United States)

    Mousavi-Zadeh, Seyyed Hamid; Rahmani, Mohammad Bagher

    2016-12-01

    In this research, rod-like undoped and Zn doped h-MoO3 thin films were grown on top of MoO3 seed layers, using hydrothermal technique without adding any surfactant. Seed layers of MoO3 were coated on top of glass substrates using spray pyrolysis technique. Structural, morphological and optical properties of thin films were examined. XRD pattern analysis showed that the seed layer has orthorhombic crystal structure. Also, it confirms the formation of hexagonal structure for thin films grown by hydrothermal. FESEM images show the formation of long, well-shaped hexagonal rod-likes. UV-Vis spectroscopy reveals band gap increasing from 3.2 eV to 3.54 eV, by increasing Zn.

  6. Properties and metathesis activity of monomeric and dimeric Mo centres variously located on γ-alumina A DFT study

    Science.gov (United States)

    Handzlik, Jarosław

    2007-05-01

    Ethene metathesis proceeding on monomeric and dimeric Mo species on the (1 0 0) and (1 1 0) γ-alumina is investigated by density functional theory, applying the cluster approach. The calculated vibrational frequencies of the surface OH groups are assigned to the experimental IR bands. It is shown that both monomeric and dimeric Mo forms can be the active sites of olefin metathesis. Metathesis activity and stability of the Mo-methylidene centres depend on their location on alumina. The differences in the sites reactivity are explained on the basis of their geometrical and electronic structure parameters. For the monomeric centres, isomerisation of the trigonal bipyramidal intermediate to the stable square pyramidal molybdacyclobutane is kinetically favoured over the cycloreversal step. The situation is opposite in the case of the dimeric species.

  7. Insulator-Metal Transition due to La Doping in Double Perovskite Sr2MnMoO6

    Institute of Scientific and Technical Information of China (English)

    刘晓峻; 黄巧建; 徐胜; 张淑仪; 罗爱华

    2004-01-01

    Resistivity, thermal diffusivity, lattice and magnetic properties of double perovskite Sr2-xLaxMnMoO6 are investigated with systematic change of La doping concentration x from 0.0 to 0.4. The insulator to metal phase transition is observed with increasing x above 0.3, suggesting that the extra electrons via substitution of La3+for Sr2+ ions occupy mainly the conduction Mo-4d band. According to the insulator to metal phase transition,the thermal diffusivity of Sr2-xLaxMnMoO6 enhances from 0.33cm2/s at x = 0.0 to 0.49cm2/s at x = 0.4. We further investigate the La doping effects on the lattice and magnetic properties.

  8. Anticorrelation between polar lattice instability and superconductivity in the Weyl semimetal candidate MoTe2

    Science.gov (United States)

    Takahashi, H.; Akiba, T.; Imura, K.; Shiino, T.; Deguchi, K.; Sato, N. K.; Sakai, H.; Bahramy, M. S.; Ishiwata, S.

    2017-03-01

    The relation between the polar structural instability and superconductivity in a Weyl semimetal candidate MoTe2 has been clarified by finely controlled physical and chemical pressure. The physical pressure as well as the chemical pressure, i.e., the Se substitution for Te, enhances the superconducting transition temperature Tc at around the critical pressure where the polar structure transition disappears. From the heat capacity and thermopower measurements, we ascribe the significant enhancement of Tc at the critical pressure to a subtle modification of the phonon dispersion or the semimetallic band structure upon the polar-to-nonpolar transition. On the other hand, the physical pressure, which strongly reduces the interlayer distance, is more effective on the suppression of the polar structural transition and the enhancement of Tc as compared with the chemical pressure, which emphasizes the importance of the interlayer coupling on the structural and superconducting instability in MoTe2.

  9. Oxygen Passivation Mediated Tunability of Trion and Excitons in MoS2

    KAUST Repository

    Gogoi, Pranjal Kumar

    2017-08-17

    Using wide spectral range in situ spectroscopic ellipsometry with systematic ultrahigh vacuum annealing and in situ exposure to oxygen, we report the complex dielectric function of MoS2 isolating the environmental effects and revealing the crucial role of unpassivated and passivated sulphur vacancies. The spectral weights of the A (1.92 eV) and B (2.02 eV) exciton peaks in the dielectric function reduce significantly upon annealing, accompanied by spectral weight transfer in a broad energy range. Interestingly, the original spectral weights are recovered upon controlled oxygen exposure. This tunability of the excitonic effects is likely due to passivation and reemergence of the gap states in the band structure during oxygen adsorption and desorption, respectively, as indicated by ab initio density functional theory calculation results. This Letter unravels and emphasizes the important role of adsorbed oxygen in the optical spectra and many-body interactions of MoS2.

  10. Phase transition and spin-resolved transport in MoS2 nanoribbons

    Science.gov (United States)

    Heshmati-Moulai, A.; Simchi, H.; Esmaeilzadeh, M.; Peeters, F. M.

    2016-12-01

    The electronic structure and transport properties of monolayer MoS2 are studied using a tight-binding approach coupled with the nonequilibrium Green's function method. A zigzag nanoribbon of MoS2 is conducting due to the intersection of the edge states with the Fermi level that is located within the bulk gap. We show that applying a transverse electric field results in the disappearance of this intersection and turns the material into a semiconductor. By increasing the electric field the band gap undergoes a two stage linear increase after which it decreases and ultimately closes. It is shown that in the presence of a uniform exchange field, this electric field tuning of the gap can be exploited to open low energy domains where only one of the spin states contributes to the electronic conductance. This introduces possibilities in designing spin filters for spintronic applications.

  11. Anomalous lattice vibrations of monolayer MoS 2 probed by ultraviolet Raman scattering

    KAUST Repository

    Liu, Hsiang Lin

    2015-01-01

    We present a comprehensive Raman scattering study of monolayer MoS2 with increasing laser excitation energies ranging from the near-infrared to the deep-ultraviolet. The Raman scattering intensities from the second-order phonon modes are revealed to be enhanced anomalously by only the ultraviolet excitation wavelength 354 nm. We demonstrate theoretically that such resonant behavior arises from a strong optical absorption that forms near the Γ point and of the band structure and an inter-valley resonant electronic scattering by the M-point phonons. These results advance our understanding of the double resonance Raman scattering process in low-dimensional semiconducting nanomaterials and provide a foundation for the technological development of monolayer MoS2 in the ultraviolet frequency range. © the Owner Societies 2015.

  12. Impact of N-plasma and Ga-irradiation on MoS2 layer in molecular beam epitaxy

    KAUST Repository

    Mishra, Pawan

    2017-01-03

    Recent interest in two-dimensional materials has resulted in ultra-thin devices based on the transfer of transition metal dichalcogenides (TMDs) onto other TMDs or III-nitride materials. In this investigation, we realized p-type monolayer (ML) MoS2, and intrinsic GaN/p-type MoS2 heterojunction by the GaN overgrowth on ML-MoS2/c-sapphire using the plasma-assisted molecular beam epitaxy. A systematic nitrogen plasma (N∗2N2*) and gallium (Ga) irradiation studies are employed to understand the individual effect on the doping levels of ML-MoS2, which is evaluated by micro-Raman and high-resolution X-Ray photoelectron spectroscopy (HRXPS) measurements. With both methods, p-type doping was attained and was verified by softening and strengthening of characteristics phonon modes E12gE2g1 and A1gA1g from Raman spectroscopy. With adequate N∗2N2*-irradiation (3 min), respective shift of 1.79 cm−1 for A1gA1g and 1.11 cm−1 for E12gE2g1 are obtained while short term Ga-irradiated (30 s) exhibits the shift of 1.51 cm−1 for A1gA1g and 0.93 cm−1 for E12gE2g1. Moreover, in HRXPS valence band spectra analysis, the position of valence band maximum measured with respect to the Fermi level is determined to evaluate the type of doping levels in ML-MoS2. The observed values of valance band maximum are reduced to 0.5, and 0.2 eV from the intrinsic value of ≈1.0 eV for N∗2N2*- and Ga-irradiated MoS2 layers, which confirms the p-type doping of ML-MoS2. Further p-type doping is verified by Hall effect measurements. Thus, by GaN overgrowth, we attained the building block of intrinsic GaN/p-type MoS2 heterojunction. Through this work, we have provided the platform for the realization of dissimilar heterostructure via monolithic approach.

  13. A first-principles study on polar hexagonal Cs2TeM3O12 (M = W, Mo): New visible-light responsive photocatalyst

    Science.gov (United States)

    Zahedi, Ehsan; Hojamberdiev, Mirabbos

    2017-08-01

    The crystal structures, electro-optical properties, and charge carrier effective masses of Cs2TeW3O12 and Cs2TeMo3O12 with hexagonal, polar and non-centrosymmetric crystal structure were investigated based on density functional theory. Cs2TeW3O12 and Cs2TeMo3O12 are found to be indirect K (1/3, 1/3, 0) → G (0, 0, 0) band gap semiconductors (Eg > 3 eV) with small effective masses of photogenerated charge carriers. The mixing of octahedrally coordinated d° transition metal cations (W6+ and Mo6+) with the filled p orbitals of the oxygen ligands leads to the formation of some W5+/Mo5+ sites and splitting of d orbitals into the partially filled t2g (dxy, dyz, and dzx) orbitals and empty eg (dz2 and dx2-y2) orbitals. The top of the valence bond is mainly contributed by O 2p orbital of the oxygen ligands mixed with the partially filled t2g orbitals of W 5d/Mo 4d, while the conduction band mainly consists of empty eg orbitals of W 5d/Mo 4d with a little contribution of O 2p orbitals. The dielectric function exhibits a slight anisotropic behavior and optical absorption peak for Cs2TeW3O12 and Cs2TeMo3O12 belonging to the strong electronic transition O 2p → W 5d/Mo 4d within the octahedral units. According to the estimated valence band and conduction band edges, Cs2TeW3O12 and Cs2TeMo3O12 can be applied as visible-light-responsive photocatalysts for the decomposition of organic pollutants and dye molecules. Also, Cs2TeMo3O12 can be used in water splitting for hydrogen generation but Cs2TeW3O12 requires further experimental studies to confirm its ability for water splitting.

  14. Elevated Temperature Tensile Tests on DU–10Mo Rolled Foils

    Energy Technology Data Exchange (ETDEWEB)

    Schulthess, Jason [Idaho National Lab. (INL), Idaho Falls, ID (United States)

    2014-09-01

    Tensile mechanical properties for uranium-10 wt.% molybdenum (U–10Mo) foils are required to support modeling and qualification of new monolithic fuel plate designs. It is expected that depleted uranium-10 wt% Mo (DU–10Mo) mechanical behavior is representative of the low enriched U–10Mo to be used in the actual fuel plates, therefore DU-10Mo was studied to simplify material processing, handling, and testing requirements. In this report, tensile testing of DU-10Mo fuel foils prepared using four different thermomechanical processing treatments were conducted to assess the impact of foil fabrication history on resultant tensile properties.

  15. Effect of Sintering Temperature of Mo Skeleton on the Contiguity and Compressive Properties of Mo-Cu IPCs

    Science.gov (United States)

    Liu, Longfei; Cao, Fuhua; Lu, Liwei; Yan, Jianhui

    2017-02-01

    Interpenetrating phase composites (IPCs) are interesting materials, in which each phase can contribute its most desirable attributes to the composite as a whole by its contiguous morphology. In the present study, molybdenum-copper (Mo-Cu) composites with interpenetrating microstructure were fabricated by open-celled porous Mo skeleton with infiltration of Cu. Effects of sintering temperature on the Mo-Mo contiguity and compressive properties of the Mo-Cu IPCs were examined. The contiguity of Mo-Mo and compressive strength increase with the sintering temperature increasing from 1473 to 1873 K, and decrease at 2073 K. Volume fraction of Cu infiltrated in Mo skeleton and failure strain of composites decrease with the sintering temperature increasing from 1473 to 1873 K and increase at 2073 K. Mutual dependency of compressive properties and contiguity of Mo-Cu IPCs are illustrated.

  16. Oxidation, Reduction, and Condensation of Alcohols over (MO3)3 (M=Mo, W) Nanoclusters

    Energy Technology Data Exchange (ETDEWEB)

    Fang, Zongtang; Li, Zhenjun; Kelley, Matthew S.; Kay, Bruce D.; Li, Shenggang; Hennigan, Jamie M.; Rousseau, Roger J.; Dohnalek, Zdenek; Dixon, David A.

    2014-10-02

    The reactions of deuterated methanol, ethanol, 1-propanol, 1-butanol, 2-propanol, 2-butanol and t-butanol over cyclic (MO3)3 (M = Mo, W) clusters were studied experimentally with temperature programmed desorption (TPD) and theoretically with coupled cluster CCSD(T) theory and density functional theory. The reactions of two alcohols per M3O9 cluster are required to provide agreement with experiment for D2O release, dehydrogenation and dehydration. The reaction begins with the elimination of water by proton transfers and forms an intermediate dialkoxy species which can undergo further reaction. Dehydration proceeds by a β hydrogen transfer to a terminal M=O. Dehydrogenation takes place via an α hydrogen transfer to an adjacent MoVI = O atom or a WVI metal center with redox involved for M = Mo and no redox for M = W. The two channels have comparable activation energies. H/D exchange to produce alcohols can take place after olefin is released or via the dialkoxy species depending on the alcohol and the cluster. The Lewis acidity of the metal center with WVI being larger than MoVI results in the increased reactivity of W3O9 over Mo3O9 for dehydrogenation and dehydration.

  17. Organic-Inorganic Hybrid Materials Based on Basket-like {Ca⊂P6Mo18O73} Cages.

    Science.gov (United States)

    Zhang, He; Yu, Kai; Lv, Jing-hua; Gong, Li-hong; Wang, Chun-mei; Wang, Chun-xiao; Sun, Di; Zhou, Bai-Bin

    2015-07-20

    Four basket-like organic-inorganic hybrids, formulated as [{Cu(II)(H2O)2}{Ca4(H2O)4(HO0.5)3(en)2}{Ca⊂P6Mo4(V)Mo14(VI)O73}]·7H2O (1), (H4bth)[{Fe(II)(H2O)}{Ca⊂P6Mo18(VI)O73}]·4H2O (2), (H2bih)3[{Cu(II)(H2O)2}{Ca⊂P6Mo2(V)Mo16(VI)O73}]·2H2O (3), (H2bib)3[{Fe(II)(H2O)2}{Ca⊂P6Mo2(V) Mo16(VI)O73}]·4H2O (4), (bth = 1,6-bis(triazole)hexane; bih = 1,6-bis(imidazol)hexane; bib = 1,4-bis(imidazole)butane) have been hydrothermally synthesized and fully characterized. Compounds 1-4 contain polyoxoanion [Ca⊂P6Mon(V)Mo18-n(VI)O73]((6+n)-) (n = 0, 2, or 4) (abbreviated as {P6Mo18O73}) as a basic building block, which is composed of a "basket body" {P2Mo14} unit and a "handle"-liked {P4Mo4} fragment encasing an alkaline-earth metal Ca(2+) cation in the cage. Compound 1 exhibits an infrequent 2D layer structure linked by the Cu(H2O)2 linker and an uncommon tetranuclear calcium complex, while compound 2 is 8-connected 2-D layers connected by binuclear {Fe2(H2O)3} segaments, which are observed for the first time as 2-D basket-like assemblies. Compounds 3 and 4 are similar 1D Z-typed chains bonded by M(H2O)2 units (M = Cu for 3 and Fe for 4). The optical band gaps of 1-4 reveal their semiconductive natures. They exhibit universal highly efficient degradation ability for typical dyes such as methylene blue, methyl orange, and rhodamine B under UV light. The lifetime and catalysis mechanism of the catalysts have been investigated. The compounds also show good bifunctional electrocatalytic behavior for oxidation of amino acids and reduction of NO2(-).

  18. Origin of the c-axis ultraincompressibility of Mo2GaC above about 15 GPa from first principles

    Science.gov (United States)

    Qing-He, Gao; Zhi-Jun, Xu; Ling, Tang; Jin, Li; An, Du; Yun-Dong, Guo; Ze-Jin, Yang

    2016-01-01

    The mechanical properties and structural evolution of Mo2GaC are calculated by first-principles under pressure. Our results unexpectedly found that the c axis is always stiffer than a axis within 0-100 GPa. An ultraincompressibility of c axis within 15-60 GPa is observed, with a contraction of about 0.2 Å, slightly larger than that of a axis (0.14 Å). The abnormal expansion of c axis and the fast decrease in a axis above about 15 GPa and 70 GPa failed to induce the structural instability, whereas such behavior caused the elastic softening in many mechanical quantities. The shrinkage anomaly of c axis is closely reflected by the internal coordinate (u) shift of Mo atom as it shows three different slopes within 0-15 GPa, 20-60 GPa, and 70-100 GPa, respectively. The longest Mo-Mo bond is responsible for the unusual shrinkage of c-axis under pressure as they experience nearly identical pressure dependences, whereas the a axis presents certain response with the variation of C-Mo bond particularly at 70 GPa. The electronic properties are investigated, including the energy band and density of states, and so on. At G point of K-M line, the energy decreases at 10 GPa first and increases at 30 GPa subsequently, the critical point is at about 15 GPa, with respective values of -0.17 of 0 GPa, -0.18 of 10 GPa, -0.16 of 15 GPa, and -0.13 of 30 GPa, respectively. This alternative energy change of G point, which is the symmetry center of the rhombic parallelogram of Ga atoms and the midpoint of the two bonded Mo atoms, convincingly reveal the origin of the anomalous ultraincompressibility of c axis as the Mo-Mo bond length shrinkage has to overcome the increasing energy barrier height. The Mo-Mo bond population and the electronegativity investigations of the Mo atom further reveal the most likely origin of the ultraincompressibility of c axis. This interesting result expects further experimental confirmation as this is the first nanolaminate ceramics compound presenting quite

  19. Bifunctional MoO3-WO3/Ag/MoO3-WO3 Films for Efficient ITO-Free Electrochromic Devices.

    Science.gov (United States)

    Dong, Wenjie; Lv, Ying; Xiao, Lili; Fan, Yi; Zhang, Nan; Liu, Xingyuan

    2016-12-14

    Dielectric-metal-dielectric (DMD) trilayer films, served as both electrochromic (EC) film and transparent conductor (TC), have exhibited great potential application in low-cost, ITO-free electrochromic devices (ECDs). However, recent reports on the DMD-based ECDs revealed that the response time and the optical modulation properties were not very satisfactory. Here, the mixed MoO3-WO3 materials were first introduced as the dielectric layer to construct an EC-TC bifunctional MoO3-WO3/Ag/MoO3-WO3 (MWAMW) film, which demonstrates strong and broad-band optical modulation in the visible light region, fast color-switching time (2.7 s for coloration and 4.1 s for bleaching), along with high coloration efficiency (70 cm(2) C(-1)). The electrical structure and electrochemical reaction kinetics analysis revealed that the improved EC performances are associated with the increased electron intervalence transition together with the fast charge-transfer and ion-diffusion dynamics.

  20. Assessment of the Tao-Mo nonempirical semilocal density functional in applications to solids and surfaces

    Science.gov (United States)

    Mo, Yuxiang; Car, Roberto; Staroverov, Viktor N.; Scuseria, Gustavo E.; Tao, Jianmin

    2017-01-01

    Recently, Tao and Mo developed a semilocal exchange-correlation density functional. The exchange part of this functional is derived from a density-matrix expansion corrected to reproduce the fourth-order gradient expansion of the exchange energy in the slowly-varying-density limit, while the correlation part is based on the Tao-Perdew-Staroverov-Scuseria (TPSS) correlation functional, with a modification for the low-density limit. In the present paper, the Tao-Mo (TM) functional is assessed by computing various properties of solids and jellium surfaces. This includes 22 lattice constants and bulk moduli, 30 band gaps, seven cohesive energies, and jellium surface exchange and correlation energies for the density parameter rs in the range from 2 to 3 bohr. Our calculations show that the TM approximation can yield consistently high accuracy for most properties considered here, with mean absolute errors (MAEs) of 0.025 Å for lattice constants, 7.0 GPa for bulk moduli, 0.08 eV/atom for cohesive energies, and 35 erg /c m2 for surface exchange-correlation energies. The MAE in band gaps is larger than that of TPSS, but slightly smaller than the errors of the local spin-density approximation, Perdew-Burke-Ernzerhof generalized gradient approximation, and revised TPSS. However, band gaps are still underestimated, particularly for large-gap semiconductors, compared to the Heyd-Scuseria-Ernzerhof nonlocal screened hybrid functional.

  1. The modulation of Schottky barriers of metal-MoS2 contacts via BN-MoS2 heterostructures.

    Science.gov (United States)

    Su, Jie; Feng, Liping; Zhang, Yan; Liu, Zhengtang

    2016-06-22

    Using first-principles calculations within density functional theory, we systematically studied the effect of BN-MoS2 heterostructure on the Schottky barriers of metal-MoS2 contacts. Two types of FETs are designed according to the area of the BN-MoS2 heterostructure. Results show that the vertical and lateral Schottky barriers in all the studied contacts, irrespective of the work function of the metal, are significantly reduced or even vanish when the BN-MoS2 heterostructure substitutes the monolayer MoS2. Only the n-type lateral Schottky barrier of Au/BN-MoS2 contact relates to the area of the BN-MoS2 heterostructure. Notably, the Pt-MoS2 contact with n-type character is transformed into a p-type contact upon substituting the monolayer MoS2 by a BN-MoS2 heterostructure. These changes of the contact natures are ascribed to the variation of Fermi level pinning, work function and charge distribution. Analysis demonstrates that the Fermi level pinning effects are significantly weakened for metal/BN-MoS2 contacts because no gap states dominated by MoS2 are formed, in contrast to those of metal-MoS2 contacts. Although additional BN layers reduce the interlayer interaction and the work function of the metal, the Schottky barriers of metal/BN-MoS2 contacts still do not obey the Schottky-Mott rule. Moreover, different from metal-MoS2 contacts, the charges transfer from electrodes to the monolayer MoS2, resulting in an increment of the work function of these metals in metal/BN-MoS2 contacts. These findings may prove to be instrumental in the future design of new MoS2-based FETs with ohmic contact or p-type character.

  2. Simulation of channel orientation dependent transport in ultra-scaled monolayer MoX2 (X = S, Se, Te) n-MOSFETs

    Science.gov (United States)

    Chang, Jiwon

    2015-04-01

    Transport properties of about 3 nm channel length monolayer MoX2 (X = S, Se, Te) n-channel metal-oxide-semiconductor field effect transistors (MOSFETs) are examined through ballistic full-band quantum transport simulations with atomistic tight-binding Hamiltonians. Our simulations reveal that single gate (SG) monolayer MoX2 MOSFETs with an approximately 2 nm gate underlap exhibit reasonable subthreshold characteristics. From these full-band simulations, we observe channel orientation dependent negative differential resistance (NDR) in the out characteristics in the ballistic transport regime. We discuss and compare NDR properties of monolayer MoX2 n-channel MOSFETs in different transport directions.

  3. A Raman spectroscopic study of a hydrated molybdate mineral ferrimolybdite, Fe2(MoO4)3·7-8H2O.

    Science.gov (United States)

    Sejkora, Jiří; Cejka, Jiří; Malíková, Radana; López, Andrés; Xi, Yunfei; Frost, Ray L

    2014-09-15

    Raman spectra of two well-defined ferrimolybdite samples, Fe2(3+)(Mo6+O4)3·7-8H2O, from the Krupka deposit (northern Bohemia, Czech Republic) and Hůrky near Rakovník occurrence (central Bohemia, Czech Republic) were studied and tentatively interpreted. Observed bands were assigned to the stretching and bending vibrations of molybdate anions, Fe-O units and water molecules. Number of Raman and infrared bands assigned to (MoO4)(2-) units and water molecules proved that symmetrically (structurally) nonequivalent (MoO4)(2-) and H2O are present in the crystal structure of ferrimolybdite. Approximate O-H⋯O hydrogen bond lengths (2.80-2.73 Å) were inferred from the published infrared spectra.

  4. First-principles study of electronic structures and stability of body-centered cubic Ti-Mo alloys by special quasirandom structures.

    Science.gov (United States)

    Sahara, Ryoji; Emura, Satoshi; Ii, Seiichiro; Ueda, Shigenori; Tsuchiya, Koichi

    2014-06-01

    The electronic structures and structural properties of body-centered cubic Ti-Mo alloys were studied by first-principles calculations. The special quasirandom structures (SQS) model was adopted to emulate the solid solution state of the alloys. The valence band electronic structures of Ti-Mo and Ti-Mo-Fe alloys were measured by hard x-ray photoelectron spectroscopy. The structural parameters and valence band photoelectron spectra were calculated using first-principles calculations. The results obtained with the SQS models showed better agreement with the experimental results than those obtained using the conventional ordered structure models. This indicates that the SQS model is effective for predicting the various properties of solid solution alloys by means of first-principles calculations.

  5. Tuning interlayer coupling in large-area heterostructures with CVD-grown MoS2 and WS2 monolayers.

    Science.gov (United States)

    Tongay, Sefaattin; Fan, Wen; Kang, Jun; Park, Joonsuk; Koldemir, Unsal; Suh, Joonki; Narang, Deepa S; Liu, Kai; Ji, Jie; Li, Jingbo; Sinclair, Robert; Wu, Junqiao

    2014-06-11

    Band offsets between different monolayer transition metal dichalcogenides are expected to efficiently separate charge carriers or rectify charge flow, offering a mechanism for designing atomically thin devices and probing exotic two-dimensional physics. However, developing such large-area heterostructures has been hampered by challenges in synthesis of monolayers and effectively coupling neighboring layers. Here, we demonstrate large-area (>tens of micrometers) heterostructures of CVD-grown WS2 and MoS2 monolayers, where the interlayer interaction is externally tuned from noncoupling to strong coupling. Following this trend, the luminescence spectrum of the heterostructures evolves from an additive line profile where each layer contributes independently to a new profile that is dictated by charge transfer and band normalization between the WS2 and MoS2 layers. These results and findings open up venues to creating new material systems with rich functionalities and novel physical effects.

  6. Synergetic effect of TeMo5O16 and MoO3 phases in MoTeOx catalysts used for the partial oxidation of propylene

    Institute of Scientific and Technical Information of China (English)

    Yiming He; Ying Wu; Weizheng Weng; Huilin Wan

    2011-01-01

    A detailed study on the synergetic effect of TeMo5O16 and MoO3 phases in the MoTeOx catalysts for the partial oxidation of propylene to acrolein has been reported in this work. It was found that both propylene conversion and acrolein selectivity increased with the addition of MoO3 to TeMo5O16. Based on the results of N2 adsorption-desorption, XRD, XPS, in-situ XRD, O2-TPO, and 2-propanol decomposition reaction, the higher catalytic performance and synergetic effect could be attributed to the enhancement of acidity and the oxygen transfer from TeMo5O16 to MoO3 phase.

  7. Elastic modulus of phases in Ti–Mo alloys

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, Wei-dong [State Key Laboratory of Powder Metallurgy, Central South University, Changsha, Hunan 410083 (China); Liu, Yong, E-mail: yonliu11@aliyun.com [State Key Laboratory of Powder Metallurgy, Central South University, Changsha, Hunan 410083 (China); Wu, Hong; Song, Min [State Key Laboratory of Powder Metallurgy, Central South University, Changsha, Hunan 410083 (China); Zhang, Tuo-yang [Metallurgical Engineering, University of Utah, Salt Lake City, UT 84112 (United States); Lan, Xiao-dong; Yao, Tian-hang [State Key Laboratory of Powder Metallurgy, Central South University, Changsha, Hunan 410083 (China)

    2015-08-15

    In this work, a series of binary Ti–Mo alloys with the Mo contents ranging from 3.2 to 12 at.% were prepared using non-consumable arc melting. The microstructures were investigated by X-ray diffraction and transmission electron microscope, and the elastic modulus was evaluated by nanoindentation testing technique. The evolution of the volume fractions of ω phase was investigated using X-ray photoelectron spectroscopy. The results indicated that the phase constitution and elastic modulus of the Ti–Mo alloys are sensitive to the Mo content. Ti–3.2Mo and Ti–8Mo alloys containing only α and β phases, respectively, have a low elastic modulus. In contrast, Ti–4.5Mo, Ti–6Mo, Ti–7Mo alloys, with different contents of ω phase, have a high elastic modulus. A simple micromechanical model was used to calculate the elastic modulus of ω phase (E{sub ω}), which was determined to be 174.354 GPa. - Highlights: • Ti–Mo alloys with the Mo contents ranging from 3.2 to 12 at.% were investigated. • XPS was used to investigate the volume fractions of ω phase. • The elastic modulus of Ti–Mo alloys is sensitive to the Mo content. • The elastic modulus of ω phase was determined to be 174.354 GPa.

  8. States of Carbon Nanotube Supported Mo-Based HDS Catalysts

    Institute of Scientific and Technical Information of China (English)

    Hongyan Shang; Chenguang Liu; Yongqiang Xu; Jieshan Qiu; Fei Wei

    2006-01-01

    The dispersion of the active phase and loading capacity of the Mo species on carbon nanotube (CNT) was studied by the XRD technique. The reducibility properties of Co-Mo catalysts in the oxide state over CNTs were investigated by TPR, while the sulfided Co-Mo/CNT catalysts were characterized by means of the XRD and LRS techniques. The activity and selectivity with respect to the hydrodesulfurization (HDS) performances on carbon nanotube supported Co-Mo catalysts were evaluated. It was found that the main active molybdenum species in the oxide state MoO3/CNT catalysts were MoO2, but not MoO3, as generally expected. The maximum loading before the formation of the bulk phase was lower than 6% (percent by mass, based on MoO3). TPR studies revealed that the active species in the oxide state Co-Mo/CNT catalysts were reduced more easily at relatively lower temperatures in comparison to those of the Co-Mo/γ-Al2O3 catalysts, indicating that the CNT support promoted or favored the reduction of the active species. The active species of a Co-Mo-0.7/CNT catalyst were more easily reduced than those of the Co-Mo/CNT catalysts with Co/Mo atomic ratios of 0.2, 0.35, and 0.5, respectively, suggesting that the Co/Mo atomic ratio has a great effect on the reducibility of the active species. It was found that the incorporation of cobalt improved the dispersion of the molybdenum species on the support, and a phenomenon of mobilization and re-dispersion had occurred during the sulfurization process, resulting in low valence state Mo3S4 and Co-MoS2.17 active phases. HDS measurements showed that the Co-Mo/CNT catalysts were more active than the Co-Mo/γ-Al2O3 ones for the desulfurization of DBT, and the hydrogenolysis/hydrogenation selectivity of the Co-Mo/CNT catalysts was also much higher than those of the Co-Mo/γ-Al2O3. The Co-Mo/CNT catalyst with a Co/Mo atomic ratio of 0.7 showed the highest activity, whereas the catalyst with a Co/Mo atomic ratio of 0.35 had the highest selectivity.

  9. Morphology and phase modifications of MoO{sub 3} obtained by metallo-organic decomposition processes

    Energy Technology Data Exchange (ETDEWEB)

    Barros Santos, Elias de; Martins de Souza e Silva, Juliana [Instituto de Quimica, Universidade Estadual de Campinas - UNICAMP, Campinas, SP (Brazil); Odone Mazali, Italo, E-mail: mazali@iqm.unicamp.br [Instituto de Quimica, Universidade Estadual de Campinas - UNICAMP, Campinas, SP (Brazil)

    2010-11-15

    Molybdenum oxide samples were prepared using different temperatures and atmospheric conditions by metallo-organic decomposition processes and were characterized by XRD, SEM and DRS UV/Vis and Raman spectroscopies. Variation in the synthesis conditions resulted in solids with different morphologies and oxygen vacancy concentrations. Intense characteristic Raman bands of crystalline orthorhombic {alpha}-MoO{sub 3}, occurring at 992 cm{sup -1} and 820 cm{sup -1}, are observed and their shifts can be related to the differences in the structure of the solids obtained. The sample obtained under nitrogen flow at 1073 K is a phase mixture of orthorhombic {alpha}-MoO{sub 3} and monoclinic {beta}-MoO{sub 3}. The characterization results suggest that the molybdenum oxide samples are non-stoichiometric and are described as MoO{sub x} with x < 2.94. Variations in the reaction conditions make it possible to tune the number of oxygen defects and the band gap of the final material.

  10. Effect of MoO3 constituents on the growth of MoS2 nanosheets by chemical vapor deposition

    Science.gov (United States)

    Wang, Xuan; Zhang, Yong Ping; Qian Chen, Zhi

    2016-06-01

    The highly crystalline and uniform MoS2 film was grown on Si substrate by a low-pressure chemical vapor deposition method using S and MoO3 as precursors at an elevated temperature. The structures and properties of MoS2 nanosheets vary greatly with the content of MoO3 constituents in the films. The nanostructured MoS2 film exhibits strong photoluminescence in the visible range. This work may provide a pathway to synthesizing MoS2 nanosheets and facilitate the development of applicable devices.

  11. MoS2 PARTICLES MODIFIED WITH POLYSTYRENE FOR PRODUCING Ni–PS/MoS2 COATINGS

    OpenAIRE

    ZHONGJIA HUANG; DANGSHENG XIONG

    2008-01-01

    The MoS2 particles were coated with polystyrene and can be written as PS/MoS2 hereinafter. Ni–PS/MoS2 coatings and Ni–MoS2 coatings were produced by PC electrodeposition technique. The surface morphology of Ni–PS/MoS2 coating was examined and compared with those of Ni–MoS2 coating. The effect of particle concentrations on the volume percent of particles incorporated in the coatings was investigated. And the microhardness of coatings was also investigated. Results show that the surface morphol...

  12. Variational Mote Carlo Study of Flat Band Ferromagnetism -- Application to CeRh_3 B_2

    OpenAIRE

    2006-01-01

    A new mechanism for ferromagnetism in CeRh_3B_2 is proposed on the basis of variational Monte Carlo results. In a one-dimensional Anderson lattice where each 4f electron hybridizes with a ligand orbital between neighboring Ce sites, ferromagnetism is stabilized due to a nearly flat band which is a mixture of conduction and 4f electron states. Because of the strong spin-orbit interaction in 4f electron states, and of considerable amount of hybridization in the nearly flat band, the magnetic mo...

  13. Effect of Surface Defect States on Valence Band and Charge Separation and Transfer Efficiency

    Science.gov (United States)

    Xu, Juan; Teng, Yiran; Teng, Fei

    2016-09-01

    Both energy band and charge separation and transfer are the crucial affecting factor for a photochemical reaction. Herein, the BiOCl nanosheets without and with surface bismuth vacancy (BOC, V-BOC) are prepared by a simple hydrothermal method. It is found that the new surface defect states caused by bismuth vacancy have greatly up-shifted the valence band and efficiently enhanced the separation and transfer rates of photogenerated electron and hole. It is amazing that the photocatalytic activity of V-BOC is 13.6 times higher than that of BOC for the degradation methyl orange (MO). We can develop an efficient photocatalyst by the introduction of defects.

  14. Electronic level alignment at the deeply buried absorber/Mo interface in chalcopyrite-based thin film solar cells

    Science.gov (United States)

    Bär, M.; Nishiwaki, S.; Weinhardt, L.; Pookpanratana, S.; Shafarman, W. N.; Heske, C.

    2008-07-01

    We have investigated the electronic structure of the absorber/back contact interface for S-free [Cu(In ,Ga)Se2 ("CIGSe")] and S-containing [Cu(In ,Ga)(S,Se)2 ("CIGSSe")] chalcopyrites with direct and inverse photoemission. Comparison of the electronic levels of the cleavage planes reveals a pronounced cliff in the conduction band at the CIG(S )Se/Mo interface. For the valence band, we find a flat alignment and a small spike for the CIGSe- and CIGSSe-based structures, respectively.

  15. Teens join the MoEDAL collaboration

    CERN Multimedia

    Stephanie Hills

    2013-01-01

    The principal investigator for any institute joining an experimental collaboration is generally a self-assured researcher with evident leadership skills and an in-depth knowledge of their subject gained over many years. Katherine Evans fits the brief in every respect, except that she is 17 years old and her research institute is the Langton Star Centre, based at the Simon Langton Grammar School for Boys. The school has just joined the MoEDAL experiment.   Teacher Becky Parker (left) with two students from the Simon Langton Grammar School for Boys in the MoEDAL experimental area. MoEDAL, the latest LHC experiment has detectors located close to the interaction point of the LHCb experiment. This new experiment is designed to search for the highly ionizing avatars of new physics at the LHC, specifically the magnetic monopole or dyon and other highly ionizing stable massive particles from a number of beyond-the-Standard-Model scenarios. MoEDAL was approved in 2010 and is due to start taking data i...

  16. MoSe2 / Polyaniline Solar Cells

    Directory of Open Access Journals (Sweden)

    H.S. Patel

    2011-01-01

    Full Text Available Solar cells have been investigated since long for harnessing the solar energy. During this decade, a new direction has come up where in the polymers have been used in the fabrication of solar cells. Polyaniline is one of the polymers which has shown potential for its applications in heterostructure solar cells. This material is being used along with the semiconductors like InSe, TiO2, Si etc. to form the photosensitive interface. In this direction, we report our investigations on the use of Molybdenum diselenide (MoSe2 as photosensitive semiconducting material in MoSe2 / polyaniline solar cells. In this paper, the preparation of MoSe2 / polyaniline solar cells has been reported. Also, the photovoltage → photocurrent characteristics of this structure have been discussed in detail in this paper. The variation of different parameters of MoSe2 / polyaniline solar cells (like open circuit voltage, short circuit current, photoconversion efficiency and fill factor with the intensity of incident illuminations has been reported in this paper. In present case, the photocurrent density was found to be around 250 µA/cm2 with the photovoltage around 8.5 mV (which is low the photoconversion efficiency was found to be around 0.7 % along with the fill factor around 0.33. The efforts have been made to explain the low values of the photoconversion efficiency.

  17. Accelerator Production Options for 99MO

    Energy Technology Data Exchange (ETDEWEB)

    Bertsche, Kirk; /SLAC

    2010-08-25

    Shortages of {sup 99}Mo, the most commonly used diagnostic medical isotope, have caused great concern and have prompted numerous suggestions for alternate production methods. A wide variety of accelerator-based approaches have been suggested. In this paper we survey and compare the various accelerator-based approaches.

  18. 78 FR 48762 - Missouri Disaster #MO-00065

    Science.gov (United States)

    2013-08-09

    ... ADMINISTRATION Missouri Disaster MO-00065 AGENCY: U.S. Small Business Administration. ACTION: Notice. SUMMARY.... ADDRESSES: Submit completed loan applications to: U.S. Small Business Administration, Processing and..., Office of Disaster Assistance, U.S. Small Business Administration, 409 3rd Street SW., Suite...

  19. Hydrogen intercalation in MoS2

    Science.gov (United States)

    Zhu, Zhen; Peelaers, Hartwin; Van de Walle, Chris G.

    2016-08-01

    We investigate the structure and energetics of interstitial hydrogen and hydrogen molecules in layered 2 H -MoS2, an issue of interest both for hydrogen storage applications and for the use of MoS2 as an (opto)electronic material. Using first-principles density functional theory we find that hydrogen interstitials are deep donors. H2 molecules are electrically inactive and energetically more stable than hydrogen interstitials. Their equilibrium position is the hollow site of the MoS2 layers. The migration barrier of a hydrogen molecule is calculated to be smaller than 0.6 eV. We have also explored the insertion energies of hydrogen molecules as a function of hydrogen concentration in MoS2. For low concentrations, additional inserted H2 molecules prefer to be located in hollow sites (on top of the center of a hexagon) in the vicinity of an occupied site. Once two molecules have been inserted, the energy cost for inserting additional H2 molecules becomes much lower. Once all hollow sites are filled, the energy cost increases, but only by a modest amount. We find that up to 13 H2 molecules can be accommodated within the same interlayer spacing of an areal 3 ×3 supercell.

  20. MoEDAL AND MAGNETIC MONOPOLES

    CERN Multimedia

    Paola Catapano

    2016-01-01

    The LHC MoEDAL experiment publishes its first paper on its search for magnetic monopoles Geneva XXXX. In a paper published by the journal JHEP today, the MoEDAL experiment at CERN narrows the window of where to search for a hypothetical particle, the magnetic monopole. Over the last decades, experiments have been trying to find evidence for magnetic monopoles at accelerators, including at CERN’s Large Hadron Collider. Such particles were first predicted by physicist Paul Dirac in the 1930s but have never been observed so far. “Today MoEDAL celebrates the release of its first physics result and joins the other LHC experiments at the discovery frontier," says Spokesperson of the MoEDAL experiment, James Pinfold. Just as electricity comes with two charges, positive and negative, so magnetism comes with two poles, North and South. The difference is that while it’s easy to isolate a positive or negative electric charge, nobody has ever seen a solitary magnetic charge, or monopole. If you

  1. Measurement of the direct CP -violating parameter ACP in the decay D<mo>+ stretchy='false'>→mo>K<mo>-mo>π<mo>+mo>π+>

    Energy Technology Data Exchange (ETDEWEB)

    Abazov, V. M.; Abbott, B.; Acharya, B. S.; Adams, M.; Adams, T.; Agnew, J. P.; Alexeev, G. D.; Alkhazov, G.; Alton, A.; Askew, A.; Atkins, S.; Augsten, K.; Avila, C.; Badaud, F.; Bagby, L.; Baldin, B.; Bandurin, D. V.; Banerjee, S.; Barberis, E.; Baringer, P.; Bartlett, J. F.; Bassler, U.; Bazterra, V.; Bean, A.; Begalli, M.; Bellantoni, L.; Beri, S. B.; Bernardi, G.; Bernhard, R.; Bertram, I.; Besançon, M.; Beuselinck, R.; Bhat, P. C.; Bhatia, S.; Bhatnagar, V.; Blazey, G.; Blessing, S.; Bloom, K.; Boehnlein, A.; Boline, D.; Boos, E. E.; Borissov, G.; Borysova, M.; Brandt, A.; Brandt, O.; Brock, R.; Bross, A.; Brown, D.; Bu, X. B.; Buehler, M.; Buescher, V.; Bunichev, V.; Burdin, S.; Buszello, C. P.; Camacho-Pérez, E.; Casey, B. C. K.; Castilla-Valdez, H.; Caughron, S.; Chakrabarti, S.; Chan, K. M.; Chandra, A.; Chapon, E.; Chen, G.; Cho, S. W.; Choi, S.; Choudhary, B.; Cihangir, S.; Claes, D.; Clutter, J.; Cooke, M.; Cooper, W. E.; Corcoran, M.; Couderc, F.; Cousinou, M. -C.; Cutts, D.; Das, A.; Davies, G.; de Jong, S. J.; De La Cruz-Burelo, E.; Déliot, F.; Demina, R.; Denisov, D.; Denisov, S. P.; Desai, S.; Deterre, C.; DeVaughan, K.; Diehl, H. T.; Diesburg, M.; Ding, P. F.; Dominguez, A.; Dubey, A.; Dudko, L. V.; Duperrin, A.; Dutt, S.; Eads, M.; Edmunds, D.; Ellison, J.; Elvira, V. D.; Enari, Y.; Evans, H.; Evdokimov, V. N.; Fauré, A.; Feng, L.; Ferbel, T.; Fiedler, F.; Filthaut, F.; Fisher, W.; Fisk, H. E.; Fortner, M.; Fox, H.; Fuess, S.; Garbincius, P. H.; Garcia-Bellido, A.; García-González, J. A.; Gavrilov, V.; Geng, W.; Gerber, C. E.; Gershtein, Y.; Ginther, G.; Gogota, O.; Golovanov, G.; Grannis, P. D.; Greder, S.; Greenlee, H.; Grenier, G.; Gris, Ph.; Grivaz, J. -F.; Grohsjean, A.; Grünendahl, S.; Grünewald, M. W.; Guillemin, T.; Gutierrez, G.; Gutierrez, P.; Haley, J.; Han, L.; Harder, K.; Harel, A.; Hauptman, J. M.; Hays, J.; Head, T.; Hebbeker, T.; Hedin, D.; Hegab, H.; Heinson, A. P.; Heintz, U.; Hensel, C.; Heredia-De La Cruz, I.; Herner, K.; Hesketh, G.; Hildreth, M. D.; Hirosky, R.; Hoang, T.; Hobbs, J. D.; Hoeneisen, B.; Hogan, J.; Hohlfeld, M.; Holzbauer, J. L.; Howley, I.; Hubacek, Z.; Hynek, V.; Iashvili, I.; Ilchenko, Y.; Illingworth, R.; Ito, A. S.; Jabeen, S.; Jaffré, M.; Jayasinghe, A.; Jeong, M. S.; Jesik, R.; Jiang, P.; Johns, K.; Johnson, E.; Johnson, M.; Jonckheere, A.; Jonsson, P.; Joshi, J.; Jung, A. W.; Juste, A.; Kajfasz, E.; Karmanov, D.; Katsanos, I.; Kaur, M.; Kehoe, R.; Kermiche, S.; Khalatyan, N.; Khanov, A.; Kharchilava, A.; Kharzheev, Y. N.; Kiselevich, I.; Kohli, J. M.; Kozelov, A. V.; Kraus, J.; Kumar, A.; Kupco, A.; Kurča, T.; Kuzmin, V. A.; Lammers, S.; Lebrun, P.; Lee, H. S.; Lee, S. W.; Lee, W. M.; Lei, X.; Lellouch, J.; Li, D.; Li, H.; Li, L.; Li, Q. Z.; Lim, J. K.; Lincoln, D.; Linnemann, J.; Lipaev, V. V.; Lipton, R.; Liu, H.; Liu, Y.; Lobodenko, A.; Lokajicek, M.; Lopes de Sa, R.; Luna-Garcia, R.; Lyon, A. L.; Maciel, A. K. A.; Madar, R.; Magaña-Villalba, R.; Malik, S.; Malyshev, V. L.; Mansour, J.; Martínez-Ortega, J.; McCarthy, R.; McGivern, C. L.; Meijer, M. M.; Melnitchouk, A.; Menezes, D.; Mercadante, P. G.; Merkin, M.; Meyer, A.; Meyer, J.; Miconi, F.; Mondal, N. K.; Mulhearn, M.; Nagy, E.; Narain, M.; Nayyar, R.; Neal, H. A.; Negret, J. P.; Neustroev, P.; Nguyen, H. T.; Nunnemann, T.; Orduna, J.; Osman, N.; Osta, J.; Pal, A.; Parashar, N.; Parihar, V.; Park, S. K.; Partridge, R.; Parua, N.; Patwa, A.; Penning, B.; Perfilov, M.; Peters, Y.; Petridis, K.; Petrillo, G.; Pétroff, P.; Pleier, M. -A.; Podstavkov, V. M.; Popov, A. V.; Prewitt, M.; Price, D.; Prokopenko, N.; Qian, J.; Quadt, A.; Quinn, B.; Ratoff, P. N.; Razumov, I.; Ripp-Baudot, I.; Rizatdinova, F.; Rominsky, M.; Ross, A.; Royon, C.; Rubinov, P.; Ruchti, R.; Sajot, G.; Sánchez-Hernández, A.; Sanders, M. P.; Santos, A. S.; Savage, G.; Savitskyi, M.; Sawyer, L.; Scanlon, T.; Schamberger, R. D.; Scheglov, Y.; Schellman, H.; Schwanenberger, C.; Schwienhorst, R.; Sekaric, J.; Severini, H.; Shabalina, E.; Shary, V.; Shaw, S.; Shchukin, A. A.; Simak, V.; Skubic, P.; Slattery, P.; Smirnov, D.; Snow, G. R.; Snow, J.; Snyder, S.; Söldner-Rembold, S.; Sonnenschein, L.; Soustruznik, K.; Stark, J.; Stoyanova, D. A.; Strauss, M.; Suter, L.; Svoisky, P.; Titov, M.; Tokmenin, V. V.; Tsai, Y. -T.; Tsybychev, D.; Tuchming, B.; Tully, C.; Uvarov, L.; Uvarov, S.; Uzunyan, S.; Van Kooten, R.; van Leeuwen, W. M.; Varelas, N.; Varnes, E. W.; Vasilyev, I. A.; Verkheev, A. Y.; Vertogradov, L. S.; Verzocchi, M.; Vesterinen, M.; Vilanova, D.; Vokac, P.; Wahl, H. D.; Wang, M. H. L. S.; Warchol, J.; Watts, G.; Wayne, M.; Weichert, J.; Welty-Rieger, L.; Williams, M. R. J.; Wilson, G. W.; Wobisch, M.; Wood, D. R.; Wyatt, T. R.; Xie, Y.; Yamada, R.; Yang, S.; Yasuda, T.; Yatsunenko, Y. A.; Ye, W.; Ye, Z.; Yin, H.; Yip, K.; Youn, S. W.; Yu, J. M.; Zennamo, J.; Zhao, T. G.; Zhou, B.; Zhu, J.; Zielinski, M.; Zieminska, D.; Zivkovic, L.

    2014-12-01

    We measure the direct CP-violating parameter ACP for the decay of the charged charm meson, Dmo>+ stretchy="false">→mo>Kmo>-mo>πmo>+mo>πmo>+> (and charge conjugate), using the full 10.4 fbmo>->1 sample of ppmo accent="true" stretchy="false">¯mo> collisions at smo>=>1.96 TeV collected by the D0 detector at the Fermilab Tevatron collider. We extract the raw reconstructed charge asymmetry by fitting the invariant mass distributions for the sum and difference of charge-specific samples. This quantity is then corrected for detector-related asymmetries using data-driven methods and for possible physics asymmetries (from Bmo stretchy="false">→mo

  2. Measurement of the direct CP -violating parameter ACP in the decay D<mo>+ stretchy='false'>→mo>K<mo>-mo>π<mo>+mo>π+>

    Energy Technology Data Exchange (ETDEWEB)

    Abazov, V. M.; Abbott, B.; Acharya, B. S.; Adams, M.; Adams, T.; Agnew, J. P.; Alexeev, G. D.; Alkhazov, G.; Alton, A.; Askew, A.; Atkins, S.; Augsten, K.; Avila, C.; Badaud, F.; Bagby, L.; Baldin, B.; Bandurin, D. V.; Banerjee, S.; Barberis, E.; Baringer, P.; Bartlett, J. F.; Bassler, U.; Bazterra, V.; Bean, A.; Begalli, M.; Bellantoni, L.; Beri, S. B.; Bernardi, G.; Bernhard, R.; Bertram, I.; Besançon, M.; Beuselinck, R.; Bhat, P. C.; Bhatia, S.; Bhatnagar, V.; Blazey, G.; Blessing, S.; Bloom, K.; Boehnlein, A.; Boline, D.; Boos, E. E.; Borissov, G.; Borysova, M.; Brandt, A.; Brandt, O.; Brock, R.; Bross, A.; Brown, D.; Bu, X. B.; Buehler, M.; Buescher, V.; Bunichev, V.; Burdin, S.; Buszello, C. P.; Camacho-Pérez, E.; Casey, B. C. K.; Castilla-Valdez, H.; Caughron, S.; Chakrabarti, S.; Chan, K. M.; Chandra, A.; Chapon, E.; Chen, G.; Cho, S. W.; Choi, S.; Choudhary, B.; Cihangir, S.; Claes, D.; Clutter, J.; Cooke, M.; Cooper, W. E.; Corcoran, M.; Couderc, F.; Cousinou, M. -C.; Cutts, D.; Das, A.; Davies, G.; de Jong, S. J.; De La Cruz-Burelo, E.; Déliot, F.; Demina, R.; Denisov, D.; Denisov, S. P.; Desai, S.; Deterre, C.; DeVaughan, K.; Diehl, H. T.; Diesburg, M.; Ding, P. F.; Dominguez, A.; Dubey, A.; Dudko, L. V.; Duperrin, A.; Dutt, S.; Eads, M.; Edmunds, D.; Ellison, J.; Elvira, V. D.; Enari, Y.; Evans, H.; Evdokimov, V. N.; Fauré, A.; Feng, L.; Ferbel, T.; Fiedler, F.; Filthaut, F.; Fisher, W.; Fisk, H. E.; Fortner, M.; Fox, H.; Fuess, S.; Garbincius, P. H.; Garcia-Bellido, A.; García-González, J. A.; Gavrilov, V.; Geng, W.; Gerber, C. E.; Gershtein, Y.; Ginther, G.; Gogota, O.; Golovanov, G.; Grannis, P. D.; Greder, S.; Greenlee, H.; Grenier, G.; Gris, Ph.; Grivaz, J. -F.; Grohsjean, A.; Grünendahl, S.; Grünewald, M. W.; Guillemin, T.; Gutierrez, G.; Gutierrez, P.; Haley, J.; Han, L.; Harder, K.; Harel, A.; Hauptman, J. M.; Hays, J.; Head, T.; Hebbeker, T.; Hedin, D.; Hegab, H.; Heinson, A. P.; Heintz, U.; Hensel, C.; Heredia-De La Cruz, I.; Herner, K.; Hesketh, G.; Hildreth, M. D.; Hirosky, R.; Hoang, T.; Hobbs, J. D.; Hoeneisen, B.; Hogan, J.; Hohlfeld, M.; Holzbauer, J. L.; Howley, I.; Hubacek, Z.; Hynek, V.; Iashvili, I.; Ilchenko, Y.; Illingworth, R.; Ito, A. S.; Jabeen, S.; Jaffré, M.; Jayasinghe, A.; Jeong, M. S.; Jesik, R.; Jiang, P.; Johns, K.; Johnson, E.; Johnson, M.; Jonckheere, A.; Jonsson, P.; Joshi, J.; Jung, A. W.; Juste, A.; Kajfasz, E.; Karmanov, D.; Katsanos, I.; Kaur, M.; Kehoe, R.; Kermiche, S.; Khalatyan, N.; Khanov, A.; Kharchilava, A.; Kharzheev, Y. N.; Kiselevich, I.; Kohli, J. M.; Kozelov, A. V.; Kraus, J.; Kumar, A.; Kupco, A.; Kurča, T.; Kuzmin, V. A.; Lammers, S.; Lebrun, P.; Lee, H. S.; Lee, S. W.; Lee, W. M.; Lei, X.; Lellouch, J.; Li, D.; Li, H.; Li, L.; Li, Q. Z.; Lim, J. K.; Lincoln, D.; Linnemann, J.; Lipaev, V. V.; Lipton, R.; Liu, H.; Liu, Y.; Lobodenko, A.; Lokajicek, M.; Lopes de Sa, R.; Luna-Garcia, R.; Lyon, A. L.; Maciel, A. K. A.; Madar, R.; Magaña-Villalba, R.; Malik, S.; Malyshev, V. L.; Mansour, J.; Martínez-Ortega, J.; McCarthy, R.; McGivern, C. L.; Meijer, M. M.; Melnitchouk, A.; Menezes, D.; Mercadante, P. G.; Merkin, M.; Meyer, A.; Meyer, J.; Miconi, F.; Mondal, N. K.; Mulhearn, M.; Nagy, E.; Narain, M.; Nayyar, R.; Neal, H. A.; Negret, J. P.; Neustroev, P.; Nguyen, H. T.; Nunnemann, T.; Orduna, J.; Osman, N.; Osta, J.; Pal, A.; Parashar, N.; Parihar, V.; Park, S. K.; Partridge, R.; Parua, N.; Patwa, A.; Penning, B.; Perfilov, M.; Peters, Y.; Petridis, K.; Petrillo, G.; Pétroff, P.; Pleier, M. -A.; Podstavkov, V. M.; Popov, A. V.; Prewitt, M.; Price, D.; Prokopenko, N.; Qian, J.; Quadt, A.; Quinn, B.; Ratoff, P. N.; Razumov, I.; Ripp-Baudot, I.; Rizatdinova, F.; Rominsky, M.; Ross, A.; Royon, C.; Rubinov, P.; Ruchti, R.; Sajot, G.; Sánchez-Hernández, A.; Sanders, M. P.; Santos, A. S.; Savage, G.; Savitskyi, M.; Sawyer, L.; Scanlon, T.; Schamberger, R. D.; Scheglov, Y.; Schellman, H.; Schwanenberger, C.; Schwienhorst, R.; Sekaric, J.; Severini, H.; Shabalina, E.; Shary, V.; Shaw, S.; Shchukin, A. A.; Simak, V.; Skubic, P.; Slattery, P.; Smirnov, D.; Snow, G. R.; Snow, J.; Snyder, S.; Söldner-Rembold, S.; Sonnenschein, L.; Soustruznik, K.; Stark, J.; Stoyanova, D. A.; Strauss, M.; Suter, L.; Svoisky, P.; Titov, M.; Tokmenin, V. V.; Tsai, Y. -T.; Tsybychev, D.; Tuchming, B.; Tully, C.; Uvarov, L.; Uvarov, S.; Uzunyan, S.; Van Kooten, R.; van Leeuwen, W. M.; Varelas, N.; Varnes, E. W.; Vasilyev, I. A.; Verkheev, A. Y.; Vertogradov, L. S.; Verzocchi, M.; Vesterinen, M.; Vilanova, D.; Vokac, P.; Wahl, H. D.; Wang, M. H. L. S.; Warchol, J.; Watts, G.; Wayne, M.; Weichert, J.; Welty-Rieger, L.; Williams, M. R. J.; Wilson, G. W.; Wobisch, M.; Wood, D. R.; Wyatt, T. R.; Xie, Y.; Yamada, R.; Yang, S.; Yasuda, T.; Yatsunenko, Y. A.; Ye, W.; Ye, Z.

    2014-12-01

    We measure the direct CP-violating parameter ACP for the decay of the charged charm meson, Dmo>+ stretchy="false">→mo>Kmo>-mo>πmo>+mo>πmo>+> (and charge conjugate), using the full 10.4 fbmo>->1 sample of ppmo accent="true" stretchy="false">¯mo> collisions at smo>=>1.96 TeV collected by the D0 detector at the Fermilab Tevatron collider. We extract the raw reconstructed charge asymmetry by fitting the invariant mass distributions for the sum and difference of charge-specific samples. This quantity is then corrected for detector-related asymmetries using data-driven methods and for possible physics asymmetries (from Bmo stretchy="false">→mo

  3. Resonant Raman spectroscopy study of swift heavy ion irradiated MoS2

    Science.gov (United States)

    Guo, Hang; Sun, Youmei; Zhai, Pengfei; Zeng, Jian; Zhang, Shengxia; Hu, Peipei; Yao, Huijun; Duan, Jinglai; Hou, Mingdong; Liu, Jie

    2016-08-01

    Molybdenum disulphide (MoS2) crystal samples were irradiated by swift heavy ions (209Bi and 56Fe). Hillock-like latent tracks were observed on the surface of irradiated MoS2 by atomic force microscopy. The modifications of properties of irradiated MoS2 were investigated by resonant Raman spectroscopy and ultraviolet-visible spectroscopy (UV-Vis). A new peak (E1u2, ∼385.7 cm-1) occurs near the in-plane E2g1 peak (∼383.7 cm-1) after irradiation. The two peaks shift towards lower frequency and broaden due to structural defects and stress with increasing fluence. When irradiated with high fluence, two other new peaks appear at ∼ 190 and ∼ 230 cm-1. The peak at ∼230 cm-1 is disorder-induced LA(M) mode. The presence of this mode indicates defects induced by irradiation. The feature at ∼460 cm-1 is composed of 2LA(M) (∼458 cm-1) and A2u (∼466 cm-1) mode. With increasing fluence, the integrated intensity ratio between 2LA(M) and A2u increases. The relative enhancement of 2LA(M) mode is in agreement with the appearance of LA(M) mode, which both demonstrate structural disorder in irradiated MoS2. The ∼423-cm-1 peak shifts toward lower frequency due to the decrease in exciton energy of MoS2, and this was demonstrated by the results of UV-Vis spectra. The decrease in exciton energy could be due to introduction of defect levels into band gap.

  4. Microstrip microwave band gap structures

    Indian Academy of Sciences (India)

    V Subramanian

    2008-04-01

    Microwave band gap structures exhibit certain stop band characteristics based on the periodicity, impedance contrast and effective refractive index contrast. These structures though formed in one-, two- and three-dimensional periodicity, are huge in size. In this paper, microstrip-based microwave band gap structures are formed by removing the substrate material in a periodic manner. This paper also demonstrates that these structures can serve as a non-destructive characterization tool for materials, a duplexor and frequency selective coupler. The paper presents both experimental results and theoretical simulation based on a commercially available finite element methodology for comparison.

  5. Fe-Mo double perovskite: From small clusters to bulk material

    Energy Technology Data Exchange (ETDEWEB)

    Carvajal, E., E-mail: ecarvajalq@ipn.mx [Instituto Politecnico Nacional, ESIME-Culhuacan, Av. Santa Ana 1000, C.P. 04430 Mexico, D.F. (Mexico); Oviedo-Roa, R. [Programa de Investigacion en Ingenieria Molecular, Instituto Mexicano del Petroleo, Eje Central Lazaro Cardenas Norte 152, 07730 Mexico, D.F. (Mexico); Cruz-Irisson, M. [Instituto Politecnico Nacional, ESIME-Culhuacan, Av. Santa Ana 1000, C.P. 04430 Mexico, D.F. (Mexico); Navarro, O. [Instituto de Investigaciones en Materiales, Universidad Nacional Autonoma de Mexico, A.P. 70-360, 04510 Mexico, D.F. (Mexico)

    2012-09-20

    To understand the differences in behaviour between up- and down-spin electrons observed in the half-metallic Sr{sub 2}FeMoO{sub 6} double perovskite, the density of states (DOS) was studied for the (FeO{sub 6}){sup -4} and (MoO{sub 6}){sup -6} octahedral clusters using first-principles density functional theory within the generalised gradient approximation (GGA) scheme and the Perdew-Burke-Ernzerhof (PBE) functional. Our results reveal that half-metallic character is present, even starting from an isolated (FeO{sub 6}){sup -4} cluster, and is a consequence of spin decoupling of antibonding hybridisations between iron t{sub 2g} states and oxygen p states (t{sub 2g}{sup a} states), i.e., t{sub 2g}{sup a} states lie below the Highest Occupied Molecular Orbital (HOMO) in the up-spin channel, whereas they lie above the HOMO level in the down-spin channel. The spin-induced shifting between up-spin and down-spin DOS situates the HOMO in such a way that the molecular orbitals oxygen p states (p bands) are fully spin-paired by octet electrons. Thus, the down-spin channel has metallic character because the HOMO lies just at the p bands, and the up-spin channel is semiconducting because the HOMO falls within the energy gap between the t{sub 2g}{sup a} and e{sub g}{sup a} bands. Finally, the (MoO{sub 6}){sup -6} octahedron does not inhibit the perovskite half-metallic character since this cluster has a zero total spin.

  6. Band head spin assignment of superdeformed bands in 86Zr

    Science.gov (United States)

    Dadwal, Anshul; Mittal, H. M.

    2016-11-01

    Two parameter expressions for rotational spectra viz. variable moment of inertia (VMI), ab formula and three parameter Harris ω 2 expansion are used to assign the band head spins (I 0) of four rotational superdeformed bands in 86Zr. The least-squares fitting method is employed to obtain the band head spins of these four bands in the A ∼ 80 mass region. Model parameters are extracted by fitting of intraband γ-ray energies, so as to obtain a minimum root-mean-square (rms) deviation between the calculated and the observed transition energies. The calculated transition energies are found to depend sensitively on the assigned spins. Whenever an accurate band head spin is assigned, the calculated transition energies are in agreement with the experimental transition energies. The dynamic moment of inertia is also extracted and its variation with rotational frequency is investigated. Since a better agreement of band head spin with experimental results is found using the VMI model, it is a more powerful tool than the ab formula and Harris ω 2 expansion.

  7. Enhanced photocatalytic activity of ZnS nanoparticles loaded with MoS{sub 2} nanoflakes by self-assembly approach

    Energy Technology Data Exchange (ETDEWEB)

    Vattikuti, S.V. Prabhakar, E-mail: vsvprabu@gmail.com; Byon, Chan, E-mail: cbyon@ynu.ac.kr; Jeon, Sora

    2016-12-01

    A hybrid consisting of ZnS nanoparticles supported on layered MoS{sub 2}−ZnS was synthesized by a hydrothermal method based on self-assembly technique without using a template. XRD, SEM-EDX, TEM, HR-TEM, TG-DTA, XPS, N{sub 2} adsorption-desorption, and UV–Vis spectroscopies were used to characterize the structural features, morphology, and composition of the MoS{sub 2}–ZnS hybrid. The results show that the MoS{sub 2}–ZnS hybrid is mainly ZnS nanoparticles on layered MoS{sub 2} with a thickness of ca. 5–20 nm. The combination of the MoS{sub 2} and ZnS hybrid structure is beneficial for enhancing the photocatalytic degradation of rhodamine B (RhB) under visible light irradiation. A possible photoreaction mechanism of the MoS{sub 2}–ZnS hybrid in the degradation is proposed. The photoexcited electrons from the ZnS could easily transfer to the conduction band of MoS{sub 2}, thus decreasing the recombination of photoinduced carriers and enabling the degradation of RhB under visible light irradiation.

  8. Study of structure of the TiO{sub 2}–MoO{sub 3} bilayer films by Raman spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Santos, Elias de Barros; Sigoli, Fernando Aparecido; Mazali, Italo Odone, E-mail: mazali@iqm.unicamp.br

    2014-12-15

    Highlights: • TiO{sub 2}–MoO{sub 3} bilayer thin films were easily prepared by dip-coating technique. • Ti and Mo metallo-organic compounds were used as source of its respective oxide. • TiO{sub 2} in anatase phase and orthorhombic phase of α-MoO{sub 3} were identified. • The bilayer structure was investigated by Raman spectroscopy. - Abstract: In this work, TiO{sub 2}–MoO{sub 3} films were easily prepared by dip-coating technique and metallo-organic decomposition process (MOD). Raman analyses indicate the formation of TiO{sub 2} in anatase phase and orthorhombic phase of α-MoO{sub 3}. It was observed that the Raman bands intensities attributed to TiO{sub 2} and MoO{sub 3} oxides were dependent on the number of decomposition–deposition cycles (DDC). The different number of DDC generates films with different thicknesses and the Raman signal was sensitive to this variation. Raman analyses provided qualitative information about the bilayer structure of the bi-component TiO{sub 2}–MoO{sub 3} films, which was confirmed by scanning electron microscopy. In this direction, the dip-coating technique and MOD process can be an efficient strategy to facile preparation of many samples to be used in applications.

  9. Construction of a 2D Graphene-Like MoS2/C3N4 Heterojunction with Enhanced Visible-Light Photocatalytic Activity and Photoelectrochemical Activity.

    Science.gov (United States)

    Yan, Jia; Chen, Zhigang; Ji, Haiyan; Liu, Zheng; Wang, Xin; Xu, Yuanguo; She, Xiaojie; Huang, Liying; Xu, Li; Xu, Hui; Li, Huaming

    2016-03-24

    A novel graphene-like MoS2 /C3N4 (GL-MoS2/C3N4) composite photocatalyst has been synthesized by a facile ethylene glycol (EG)-assisted solvothermal method. The structure and morphology of this GL-MoS2/C3N4 photocatalyst have been investigated by a wide range of characterization methods. The results showed that GL-MoS2 was uniformly distributed on the surface of GL-C3N4 forming a heterostructure. The obtained composite exhibited strong absorbing ability in the ultraviolet (UV) and visible regions. When irradiated with visible light, the composite photocatalyst showed high activity superior to those of the respective individual components GL-MoS2 and GL-C3N4 in the degradation of methyl orange. The enhanced photocatalytic activity of the composite may be attributed to the efficient separation of electron-hole pairs as a result of the matching band potentials between GL-MoS2 and GL-C3N4. Furthermore, a photocatalytic mechanism for the composite material has been proposed, and the photocatalytic reaction kinetics has been measured. Moreover, GL-MoS2/C3N4 could serve as a novel sensor for trace amounts of Cu(2+) since it exhibited good selectivity for Cu(2+) detection in water.

  10. X-ray diffraction and photoelectron spectroscopy studies of MoO 2 as catalyst for the partial oxidation of isooctane

    Science.gov (United States)

    Marin-Flores, Oscar; Scudiero, L.; Ha, Su

    2009-08-01

    X-ray diffraction (XRD), X-ray photoemission (XPS) as well as ultraviolet photoemission (UPS) spectroscopy experiments on MoO 2 powders were carried out to examine the bulk, the core level energies, and the electronic structure of MoO 2 samples that were employed as catalysts for the partial oxidation of isooctane. Five fresh 0.5-g MoO 2 samples were exposed for 0, 0.5, 9, 20, and 43 h to identical reforming environments and their spent samples were analyzed using the techniques mentioned above. Our results indicate the rapid appearance of an intermediate Mo phase with a binding energy of 228.5 eV and whose concentration progressively increases with time. The oxidation state for this new phase was graphically estimated to approximately +2.6 and assigned to the compound Mo 2O 3, which forms on the catalyst surface as a result of its exposure to the reforming environment. The electronic structure probed by UPS reveals two bands, one at 1.62 eV and another at 0.55 eV below the Fermi level, that decrease with the increasing time on stream. These results correlate very well with the drop in the catalytic performance of MoO 2 for the partial oxidation of isooctane and with the decline in the concentration of dioxide (Mo 4+) detected not only on the catalyst surface, but also in the bulk structure, as confirmed by our XRD analysis.

  11. Al{sub 2}O{sub 3} as a suitable substrate and a dielectric layer for n-layer MoS{sub 2}

    Energy Technology Data Exchange (ETDEWEB)

    Singh, Arunima K., E-mail: arunima.singh@nist.gov; Davydov, Albert V.; Tavazza, Francesca [Materials Science and Engineering Division, National Institute of Standards and Technology, Gaithersburg, Maryland 20899 (United States); Hennig, Richard G. [Materials Science and Engineering, University of Florida, Gainesville, Florida 32611 (United States)

    2015-08-03

    Sapphire (α-Al{sub 2}O{sub 3}) is a common substrate for the growth of single- to few-layer MoS{sub 2} films, and amorphous aluminium oxide serves as a high-κ dielectric gate oxide for MoS{sub 2} based transistors. Using density-functional theory calculations with a van der Waals functional, we investigate the structural, energetic, and electronic properties of n-layer MoS{sub 2} (n = 1and 3) on the α-Al{sub 2}O{sub 3} (0001) surface. Our results show that the sapphire stabilizes single-layer and tri-layer MoS{sub 2}, while having a negligible effect on the structure, band gap, and electron effective masses of MoS{sub 2}. This combination of a strong energetic stabilization and weak perturbation of the electronic properties shows that α-Al{sub 2}O{sub 3} can serve as an ideal substrate for depositing ultra-thin MoS{sub 2} layers and can also serve as a passivation or gate-oxide layer for MoS{sub 2} based devices.

  12. Electronic and optical properties of β'-Tb2(MoO4)3: DFT+U approach

    Science.gov (United States)

    Reshak, A. H.

    2016-11-01

    The ground state properties of β'-Tb2(MoO4)3 are investigated using the density functional theory plus U-Hubbard Hamiltonian. To ascertain the influence of the spin-polarization on the ground state properties of orthorhombic β'-Tb2(MoO4)3, we have performed spin-polarization calculations and the spin-polarized electronic band structure for spin-up (↑) and spin-down (↓) are calculated. It has been found that for spin-up (↑) and spin-down (↓) the β'-Tb2(MoO4)3 compound possesses indirect energy band gap, as the valence band maximum (VBM) is located at Y point of the Brillouin zone (BZ) and the conduction band minimum (CBM) at the center of the BZ. The calculated value of the band gap is 3.61 eV for spin-up (↑) and spin-down (↓), and it is in close agreement with the measured one (3.76 eV). It is clear that the electronic band structure for spin-up (↑) and spin-down (↓) cases presents identical configuration. Therefore, we can conclude that the spin-polarization has identical influence on the ground state properties of β'-Tb2(MoO4)3. To ascertain this observation, we have presented and explained the necessary ingredients of the calculated total and atom-resolved density of states. It has been noticed that the calculated total density of states (TDOS) for spin-up (↑) and spin-down (↓) cases are identical confirming that the spin-polarization has identical influence on the ground state properties of β'-Tb2(MoO4)3. For more details, in order to have deep insight into the electronic structure, we have presented the atom-resolved density of states which show identical features for spin-up (↑) and spin-down (↓). The angular momentum projected density of states (PDOS) helps to identify the angular momentum character of the various structures. To obtain more details about the electronic structure and, hence, the ground state properties, the complex first-order linear optical dispersion is calculated for spin-up (↑) and spin-down (↓) cases to

  13. Surface, optical characteristics and photocatalytic ability of Scheelite-type monoclinic Bi{sub 3}FeMo{sub 2}O{sub 12} nanoparticles

    Energy Technology Data Exchange (ETDEWEB)

    Nie, Xinming, E-mail: nxinming@jsnu.edu.cn; Wulayin, Wumitijiang; Song, Tingting; Wu, Minxiao; Qiao, Xuebin, E-mail: qiaoxb@jsnu.edu.cn

    2016-11-30

    Highlights: • Scheelite-type photocatalyst Bi{sub 3}FeMo{sub 2}O{sub 12} with B-superstructure was developed. • Bi{sub 3}FeMo{sub 2}O{sub 12} has high efficient optical absorption in visible wavelength region. • The narrow band energy 2.3 eV was characterized by direct allowed type. • It presents efficient photodegradation on RhB dye solution driven by visible-light. - Abstract: Bi{sub 3}FeMo{sub 2}O{sub 12} nanoparticles with the Scheelite-type monoclinic structure were prepared by the Pechini synthesis. The Bi{sub 3}FeMo{sub 2}O{sub 12} nanoparticle has a size of about 50 nm. The phase formation and structural characteristic were studied by X-ray diffraction (XRD) patterns and Rietveld refinements. The Scheelite framework is characterized by a superstructure constructed by the ordered arrangement of Fe/Mo tetrahedral on the B sites. The surface characteristics of Bi{sub 3}FeMo{sub 2}O{sub 12} nanoparticles were studied by the measurements such as the scanning electron microscope (SEM), the transmission electron microscopy (TEM), and the N{sub 2}-adsorption–desorption isotherm. Bi{sub 3}FeMo{sub 2}O{sub 12} nanoparticles present an efficient optical absorption in a wide wavelength region from UV to 540 nm. The band gap energy was decided to be 2.3 eV and characterized by a direct allowed electronic optical transition. The photocatalytic activity of Bi{sub 3}FeMo{sub 2}O{sub 12} nanoparticles was confirmed by the photodegradation of the rhodamine B (RhB) dye solution. The experiments indicate that the Scheelite-type molybdate could be a potential candidate of a visible-light-driven photocatalyst.

  14. Road and Street Centerlines - MO 2009 August MoDOT Roads - Routes (SHP)

    Data.gov (United States)

    NSGIC GIS Inventory (aka Ramona) — The MoDOT travelways coverage is based on a Dynamic Segmentation model. Dynamic Segmentation models linear features using routes and events, associating multiple...

  15. Road and Street Centerlines - MO 2009 March MoDOT Roads - Routes (SHP)

    Data.gov (United States)

    NSGIC GIS Inventory (aka Ramona) — The MoDOT roadway coverage is based on a Dynamic Segmentation model. Dynamic Segmentation models linear features using routes and events, associating multiple sets...

  16. Road and Street Centerlines - MO 2008 August MoDOT Roads - Arcs (SHP)

    Data.gov (United States)

    NSGIC GIS Inventory (aka Ramona) — The MoDOT roadway coverage is based on a Dynamic Segmentation model. Dynamic Segmentation models linear features using routes and events, associating multiple sets...

  17. Road and Street Centerlines - MO 2009 January MoDOT Roads - Routes (SHP)

    Data.gov (United States)

    NSGIC GIS Inventory (aka Ramona) — The MoDOT roadway coverage is based on a Dynamic Segmentation model. Dynamic Segmentation models linear features using routes and events, associating multiple sets...

  18. Road and Street Centerlines - MO 2008 August MoDOT Roads - Routes (SHP)

    Data.gov (United States)

    NSGIC GIS Inventory (aka Ramona) — The MoDOT roadway coverage is based on a Dynamic Segmentation model. Dynamic Segmentation models linear features using routes and events, associating multiple sets...

  19. Road and Street Centerlines - MO 2004 MoDOT Roads (SHP)

    Data.gov (United States)

    NSGIC GIS Inventory (aka Ramona) — The MoDOT roadway coverage is based on a Dynamic Segmentation model. Dynamic Segmentation models linear features using routes and events, associating multiple sets...

  20. Road and Street Centerlines - MO 2009 June MoDOT Roads - Routes (SHP)

    Data.gov (United States)

    NSGIC GIS Inventory (aka Ramona) — The MoDOT roadway coverage is based on a Dynamic Segmentation model. Dynamic Segmentation models linear features using routes and events, associating multiple sets...

  1. β-K3Fe(MoO42Mo2O7

    Directory of Open Access Journals (Sweden)

    Amira Souilem

    2014-07-01

    Full Text Available The title compound, tripotassium iron(III bis(orthomolybdate dimolybdate, was obtained by a solid-state reaction. The main structural building units are one FeO6 octahedron, two MoO4 tetrahedra and one Mo2O7 dimolybdate group, all with point group symmetries m. These units are linked via corner-sharing to form ribbons parallel to [010]. The three K+ cations are located between the ribbons on mirror planes and have coordination numbers of 10 and 12. Two O atoms of one of the MoO4 tetrahedra of the dimolybdate group are disordered over two positions in a 0.524 (11:0.476 (11 ratio. The structure of the title compound is compared briefly with that of Rb3FeMo4O15.

  2. Road and Street Centerlines - MO 2009 March MoDOT Roads - Arcs (SHP)

    Data.gov (United States)

    NSGIC GIS Inventory (aka Ramona) — The MoDOT roadway coverage is based on a Dynamic Segmentation model. Dynamic Segmentation models linear features using routes and events, associating multiple sets...

  3. Road and Street Centerlines - MO 2008 November MoDOT Roads - Arcs (SHP)

    Data.gov (United States)

    NSGIC GIS Inventory (aka Ramona) — The MoDOT roadway coverage is based on a Dynamic Segmentation model. Dynamic Segmentation models linear features using routes and events, associating multiple sets...

  4. Road and Street Centerlines - MO 2008 June MoDOT Roads - Routes (SHP)

    Data.gov (United States)

    NSGIC GIS Inventory (aka Ramona) — The MoDOT roadway coverage is based on a Dynamic Segmentation model. Dynamic Segmentation models linear features using routes and events, associating multiple sets...

  5. Road and Street Centerlines - MO 2009 June MoDOT Roads - Arcs (SHP)

    Data.gov (United States)

    NSGIC GIS Inventory (aka Ramona) — The MoDOT roadway coverage is based on a Dynamic Segmentation model. Dynamic Segmentation models linear features using routes and events, associating multiple sets...

  6. Road and Street Centerlines - MO 2008 June MoDOT Roads - Arcs (SHP)

    Data.gov (United States)

    NSGIC GIS Inventory (aka Ramona) — The MoDOT roadway coverage is based on a Dynamic Segmentation model. Dynamic Segmentation models linear features using routes and events, associating multiple sets...

  7. Road and Street Centerlines - MO 2009 January MoDOT Roads - Arcs (SHP)

    Data.gov (United States)

    NSGIC GIS Inventory (aka Ramona) — The MoDOT roadway coverage is based on a Dynamic Segmentation model. Dynamic Segmentation models linear features using routes and events, associating multiple sets...

  8. Road and Street Centerlines - MO 2009 August MoDOT Roads - Arcs (SHP)

    Data.gov (United States)

    NSGIC GIS Inventory (aka Ramona) — The MoDOT travelways coverage is based on a Dynamic Segmentation model. Dynamic Segmentation models linear features using routes and events, associating multiple...

  9. Road and Street Centerlines - MO 2008 November MoDOT Roads - Routes (SHP)

    Data.gov (United States)

    NSGIC GIS Inventory (aka Ramona) — The MoDOT roadway coverage is based on a Dynamic Segmentation model. Dynamic Segmentation models linear features using routes and events, associating multiple sets...

  10. Road and Street Centerlines - MO 2008 July MoDOT Roads - Arcs (SHP)

    Data.gov (United States)

    NSGIC GIS Inventory (aka Ramona) — The MoDOT roadway coverage is based on a Dynamic Segmentation model. Dynamic Segmentation models linear features using routes and events, associating multiple sets...

  11. Road and Street Centerlines - MO 2007 July MoDOT Roads (SHP)

    Data.gov (United States)

    NSGIC GIS Inventory (aka Ramona) — The MoDOT roadway coverage is based on a Dynamic Segmentation model. Dynamic Segmentation models linear features using routes and events, associating multiple sets...

  12. Road and Street Centerlines - MO 2008 July MoDOT Roads - Routes (SHP)

    Data.gov (United States)

    NSGIC GIS Inventory (aka Ramona) — The MoDOT roadway coverage is based on a Dynamic Segmentation model. Dynamic Segmentation models linear features using routes and events, associating multiple sets...

  13. Photo- and Electrochromic Properties of Activated Reactive Evaporated MoO3 Thin Films Grown on Flexible Substrates

    Directory of Open Access Journals (Sweden)

    K. Hari Krishna

    2008-01-01

    Full Text Available The molybdenum trioxide (MoO3 thin films were grown onto ITO-coated flexible Kapton substrates using plasma assisted activated reactive evaporation technique. The film depositions were carried out at constant glow power and oxygen partial pressures of 8 W and 1×10−3 Torr, respectively. The influence of substrate temperature on the microstructural and optical properties was investigated. The MoO3 thin films prepared at a substrate temperature of 523 K were found to be composed of uniformly distributed nanosized grains with an orthorhombic structure of α-MoO3. These nanocrystalline MoO3 thin films exhibited higher optical transmittance of about 80% in the visible region with an evaluated optical band gap of 3.29 eV. With the insertion of 12.5 mC/cm2, the films exhibited an optical modulation of 40% in the visible region with coloration efficiency of 22 cm2/C at the wavelength of 550 nm. The MoO3 films deposited at 523 K demonstrated better photochromic properties and showed highest color center concentration for the irradiation time of 30 minutes at 100 mW/cm2.

  14. Photoluminescence of monolayer MoS2 on LaAlO3 and SrTiO3 substrates.

    Science.gov (United States)

    Li, Yuanyuan; Qi, Zeming; Liu, Miao; Wang, Yuyin; Cheng, Xuerui; Zhang, Guobin; Sheng, Liusi

    2014-12-21

    In an atomically thin-film/dielectric-substrate heterostructure, the elemental physical properties of the atomically thin-film are influenced by the interaction between the thin-film and the substrate. In this article, utilizing monolayer MoS(2) on LaAlO(3) and SrTiO(3) substrates, as well as SiO2 and Gel-film as reference substrates similar to previously reported work [Nano Res, 2014, 7, 561], we systematically investigate the substrate effect on the photoluminescence of monolayer MoS(2). We observed significantly substrate-dependant photoluminescence of monolayer MoS(2), originating from substrate-to-film charge transfer. We found that SiO2 substrate introduces the most charge doping while SrTiO(3) introduces less charge transfer. Through the selection of desired substrate, we are able to induce different amounts of charge into the monolayer MoS(2), which consequently modifies the neutral exciton and charged exciton (trion) emissions. Finally, we proposed a band-diagram model to elucidate the relation between charge transfer and the substrate Fermi level and work function. Our work demonstrates that the substrate charge transfer exerts a strong influence on the monolayer MoS(2) photoluminescence property, which should be considered during device design and application. The work also provides a possible route to modify the thin-film photoluminescence property via substrate engineering for future device design.

  15. New ordered MAX phase Mo2TiAlC2: Elastic and electronic properties from first-principles

    Science.gov (United States)

    Hadi, M. A.; Ali, M. S.

    2016-10-01

    First-principles computation on the basis of density functional theory (DFT) is executed with the CASTEP code to explore the structural, elastic, and electronic properties along with Debye temperature and theoretical Vickers’ hardness of newly discovered ordered MAX phase carbide Mo2TiAlC2. The computed structural parameters are very reasonable compared with the experimental results. The mechanical stability is verified by using the computed elastic constants. The brittleness of the compound is indicated by both the Poisson’s and Pugh’s ratios. The new MAX phase is capable of resisting the pressure and tension and also has the clear directional bonding between atoms. The compound shows significant elastic anisotropy. The Debye temperature estimated from elastic moduli (B, G) is found to be 413.6 K. The electronic structure indicates that the bonding nature of Mo2TiAlC2 is a mixture of covalent and metallic with few ionic characters. The electron charge density map shows a strong directional Mo-C-Mo covalent bonding associated with a relatively weak Ti-C bond. The calculated Fermi surface is due to the low-dispersive Mo 4d-like bands, which makes the compound a conductive one. The hardness of the compound is also evaluated and a high value of 9.01 GPa is an indication of its strong covalent bonding.

  16. Quasi 2D electronic states with high spin-polarization in centrosymmetric MoS2 bulk crystals

    Science.gov (United States)

    Gehlmann, Mathias; Aguilera, Irene; Bihlmayer, Gustav; Młyńczak, Ewa; Eschbach, Markus; Döring, Sven; Gospodarič, Pika; Cramm, Stefan; Kardynał, Beata; Plucinski, Lukasz; Blügel, Stefan; Schneider, Claus M.

    2016-06-01

    Time reversal dictates that nonmagnetic, centrosymmetric crystals cannot be spin-polarized as a whole. However, it has been recently shown that the electronic structure in these crystals can in fact show regions of high spin-polarization, as long as it is probed locally in real and in reciprocal space. In this article we present the first observation of this type of compensated polarization in MoS2 bulk crystals. Using spin- and angle-resolved photoemission spectroscopy (ARPES), we directly observed a spin-polarization of more than 65% for distinct valleys in the electronic band structure. By additionally evaluating the probing depth of our method, we find that these valence band states at the point in the Brillouin zone are close to fully polarized for the individual atomic trilayers of MoS2, which is confirmed by our density functional theory calculations. Furthermore, we show that this spin-layer locking leads to the observation of highly spin-polarized bands in ARPES since these states are almost completely confined within two dimensions. Our findings prove that these highly desired properties of MoS2 can be accessed without thinning it down to the monolayer limit.

  17. Quasi 2D electronic states with high spin-polarization in centrosymmetric MoS2 bulk crystals.

    Science.gov (United States)

    Gehlmann, Mathias; Aguilera, Irene; Bihlmayer, Gustav; Młyńczak, Ewa; Eschbach, Markus; Döring, Sven; Gospodarič, Pika; Cramm, Stefan; Kardynał, Beata; Plucinski, Lukasz; Blügel, Stefan; Schneider, Claus M

    2016-06-01

    Time reversal dictates that nonmagnetic, centrosymmetric crystals cannot be spin-polarized as a whole. However, it has been recently shown that the electronic structure in these crystals can in fact show regions of high spin-polarization, as long as it is probed locally in real and in reciprocal space. In this article we present the first observation of this type of compensated polarization in MoS2 bulk crystals. Using spin- and angle-resolved photoemission spectroscopy (ARPES), we directly observed a spin-polarization of more than 65% for distinct valleys in the electronic band structure. By additionally evaluating the probing depth of our method, we find that these valence band states at the point in the Brillouin zone are close to fully polarized for the individual atomic trilayers of MoS2, which is confirmed by our density functional theory calculations. Furthermore, we show that this spin-layer locking leads to the observation of highly spin-polarized bands in ARPES since these states are almost completely confined within two dimensions. Our findings prove that these highly desired properties of MoS2 can be accessed without thinning it down to the monolayer limit.

  18. NaGd(MoO4)2 nanocrystals with diverse morphologies: controlled synthesis, growth mechanism, photoluminescence and thermometric properties

    Science.gov (United States)

    Li, Anming; Xu, Dekang; Lin, Hao; Yang, Shenghong; Shao, Yuanzhi; Zhang, Yueli

    2016-08-01

    Pure tetragonal phase, uniform and well-crystallized sodium gadolinium molybdate (NaGd(MoO4)2) nanocrystals with diverse morphologies, e.g. nanocylinders, nanocubes and square nanoplates have been selectively synthesized via oleic acid-mediated hydrothermal method. The phase, structure, morphology and composition of the as-synthesized products are studied. Contents of both sodium molybdate and oleic acid of the precursor solutions are found to affect the morphologies of the products significantly, and oleic acid plays a key role in the morphology-controlled synthesis of NaGd(MoO4)2 nanocrystals with diverse morphologies. Growth mechanism of NaGd(MoO4)2 nanocrystals is proposed based on time-dependent morphology evolution and X-ray diffraction analysis. Morphology-dependent down-shifting photoluminescence properties of NaGd(MoO4)2: Eu3+ nanocrystals, and upconversion photoluminescence properties of NaGd(MoO4)2: Yb3+/Er3+ and Yb3+/Tm3+ nanoplates are investigated in detail. Charge transfer band in the down-shifting excitation spectra shows a slight blue-shift, and the luminescence intensities and lifetimes of Eu3+ are decreased gradually with the morphology of the nanocrystals varying from nanocubes to thin square nanoplates. Upconversion energy transfer mechanisms of NaGd(MoO4)2: Yb3+/Er3+, Yb3+/Tm3+ nanoplates are proposed based on the energy level scheme and power dependence of upconversion emissions. Thermometric properties of NaGd(MoO4)2: Yb3+/Er3+ nanoplates are investigated, and the maximum sensitivity is determined to be 0.01333 K-1 at 285 K.

  19. Effects of Potassium Doping on CO Hydrogenation Over MoS2 Catalysts: A First-Principles Investigation

    Energy Technology Data Exchange (ETDEWEB)

    Andersen, Amity; Kathmann, Shawn M.; Lilga, Michael A.; Albrecht, Karl O.; Hallen, Richard T.; Mei, Donghai

    2014-07-01

    Periodic density functional theory calculations were performed to explore the effects of doping potassium (K) on the reactivity of CO hydrogenation to mixed higher alcohols over MoS2 catalysts. We found that the doped K species over the model MoS2(100) catalyst surface acts as a unique site for CO adsorption where either the K-C or the K-O bonding is allowed. The charge transfer from the K 4s electron to the conduction band of the MoS2(100) surface slightly enhances CO adsorption at the edge Mo sites. Due to the large electropositive nature, the presence of the surface K species, however, will hinder the dissociative adsorption of hydrogen. As a result, the doping K species drive CO hydrogenation selectivity toward the C2+ alcohols instead of hydrocarbons by increasing CO and decreasing hydrogen coverages on the MoS2 catalysts. To further elucidate the effect of doping K on the shifting of the selectivity toward CO hydrogenation, we calculated several key reaction steps leading to the H2CCO precursor formation, i.e., CO hydrogenation, the C-O bond scission and the C-C coupling (CH2+CO). The C-C coupling step is favorable for both the Mo and S edges. However, the undoped S edge has an overall more thermodynamically favorable reaction profile up to C-O scission compared with the Mo edge. This work was funded by a CRADA project (No. PNNL/297) with Range Fuels. The research was performed using EMSL, a national scientific user facility sponsored by the Department of Energy's Office of Biological and Environmental Research and located at Pacific Northwest National Laboratory. The work involving the results analysis and mansucript writing was supported by the US Department of Energy, Office of Basic Energy Sciences, Division of Chemical Sciences, Geosciences & Biosciences.

  20. Sulphur-bridged ruthenium-molybdenum complexes: [(R-aapm)2Ru(-S)2 Mo(OH)2]. Synthesis, spectroscopic and electro-chemical characterization. R-aapm = 2-(arylazo)pyrimidine

    Indian Academy of Sciences (India)

    Prithwiraj Byabartta

    2006-03-01

    The reaction of ctc-[Ru(R-aapm)2Cl2] (1) with (NH4)2MoS4 in aqueous MeOH afforded redviolet mixed ligand complexes of the type [(R-aapm)2Ru(-S)2Mo(OH)2] (2a-2e) [R-aapm = 2-(arylazo) pyrimidine, -R-C6H4-N=N-C4H3NN, R = H (2a), Me (2b), Cl (2c), OMe (2d), NO2 (2e)]. In complexes (2a-2e) the terminal Mo=S bonds of the MoS$_{4}^{2-}$ unit get hydroxylated and the molybdenum ion is reduced from the starting MoVI in MoS$_{4}^{2-}$ to MoIV in the final product. The solution electronic spectra exhibit a strong MLCT band at 550-570 nm in DCM. The 1H NMR spectra confirms the geometry of the complexes as being that of cis-trans-cis isomers. Cyclic voltammograms show a Ru(III)/Ru(II) couple at 1.10-1.4 V, irreversible Mo(IV)/Mo(V) oxidations in the 1.66-1.72 V range, along with four successive reversible ligand reductions in the range -0.45-0.67 V (one electron), -0.82-1.12 V (one electron), -1.44-1.90 V (simultaneously two electrons).

  1. Electron microscopy studies on MoS2 nanocrystals

    DEFF Research Database (Denmark)

    Hansen, Lars Pilsgaard

    Industrial-style MoS2-based hydrotreating catalysts are studied using electron microscopy. The MoS2 nanostructures are imaged with single-atom sensitivity to reveal the catalytically important edge structures. Furthermore, the in-situ formation of MoS2 crystals is imaged for the first time....

  2. Auger Spectroscopy Analysis of Spalled LEU-10Mo Foils

    Energy Technology Data Exchange (ETDEWEB)

    Lawrence, Samantha Kay [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Schulze, Roland K. [Los Alamos National Lab. (LANL), Los Alamos, NM (United States)

    2017-08-03

    Presentation includes slides on Surface Science used to probe LEU-10Mo Spall; Auger highlights graphitic-like inclusions and Mo-deficient oxide on base metal; Higher C concentration detected within spall area Images Courtesy; Depth profiling reveals thick oxide; Mo concentration nears nominal only at depths ~400 nm; and lastly Key Findings.

  3. Electron microscopy studies on MoS2 nanocrystals

    DEFF Research Database (Denmark)

    Hansen, Lars Pilsgaard

    Industrial-style MoS2-based hydrotreating catalysts are studied using electron microscopy. The MoS2 nanostructures are imaged with single-atom sensitivity to reveal the catalytically important edge structures. Furthermore, the in-situ formation of MoS2 crystals is imaged for the first time....

  4. Influence of Mo on the Fe:Mo:C nanocatalyst thermodynamics for single-walled carbon nanotube growth

    Science.gov (United States)

    Curtarolo, Stefano; Awasthi, Neha; Setyawan, Wahyu; Jiang, Aiqin; Bolton, Kim; Tokune, Toshio; Harutyunyan, Avetik R.

    2008-08-01

    We explore the role of Mo in Fe:Mo nanocatalyst thermodynamics for low-temperature chemical-vapor deposition growth of single-walled carbon nanotubes (SWCNTs). By using the size-pressure approximation and ab initio modeling, we prove that for both Fe-rich ( ˜80% Fe or more) and Mo-rich ( ˜50% Mo or more) Fe:Mo clusters, the presence of carbon in the cluster causes nucleation of Mo2C . This enhances the activity of the particle since it releases Fe, which is initially bound in a stable Fe:Mo phase, so that it can catalyze SWCNT growth. Furthermore, the presence of small concentrations of Mo reduces the lower size limit of low-temperature steady-state growth from ˜0.58nm for pure Fe particles to ˜0.52nm . Our ab initio-thermodynamic modeling explains experimental results and establishes a direction to search for better catalysts.

  5. Gate-tunable and thickness-dependent electronic and thermoelectric transport in few-layer MoS2

    Science.gov (United States)

    Kayyalha, Morteza; Maassen, Jesse; Lundstrom, Mark; Shi, Li; Chen, Yong P.

    2016-10-01

    Over the past few years, there has been a growing interest in layered transition metal dichalcogenides such as molybdenum disulfide (MoS2). Most studies so far have focused on the electronic and optoelectronic properties of single-layer MoS2, whose band structure features a direct bandgap, in sharp contrast to the indirect bandgap of thicker MoS2. In this paper, we present a systematic study of the thickness-dependent electrical and thermoelectric properties of few-layer MoS2. We observe that the electrical conductivity ( σ) increases as we reduce the thickness of MoS2 and peaks at about two layers, with six-times larger conductivity than our thickest sample (23-layer MoS2). Using a back-gate voltage, we modulate the Fermi energy ( E F ) of the sample where an increase in the Seebeck coefficient ( S ) is observed with decreasing gate voltage ( E F ) towards the subthreshold (OFF state) of the device, reaching as large as 500 μ V / K in a four-layer MoS2. While previous reports have focused on a single-layer MoS2 and measured Seebeck coefficient in the OFF state, which has vanishing electrical conductivity and thermoelectric power factor ( P F = S 2 σ ), we show that MoS2-based devices in their ON state can have P F as large as > 50 /μ W cm K 2 in the two-layer sample. The P F increases with decreasing thickness and then drops abruptly from double-layer to single-layer MoS2, a feature we suggest as due to a change in the energy dependence of the electron mean-free-path according to our theoretical calculation. Moreover, we show that care must be taken in thermoelectric measurements in the OFF state to avoid obtaining erroneously large Seebeck coefficients when the channel resistance is very high. Our study paves the way towards a more comprehensive examination of the thermoelectric performance of two-dimensional (2D) semiconductors.

  6. A systematic first principle method to study magnetic properties of FeMo, CoMo and NiMo

    CERN Document Server

    Bhattacharjee, A K; Halder, A; Mookerjee, A; Touheed, M

    2003-01-01

    We use the first principle TB-LMTO (Tight-Binding Linear Muffin Tin Orbital) method combined with the ASM (Augmented Space Method) to take care of disorder beyond the mean field (CPA - Cohetent Potential Approximation) approximation. We analyze binary alloys between magnetic transition metals Fe, Co, Ni and non-magnetic Mo to find out the effect of disorder on electronic structure and consequently magnetic properties of the alloys.

  7. Tunable electronic structure in stained two dimensional van der Waals g-C2N/XSe2 (X = Mo, W) heterostructures

    Science.gov (United States)

    Zheng, Z. D.; Wang, X. C.; Mi, W. B.

    2017-10-01

    The electronic structure of the strained g-C2N/XSe2 (X=Mo, W) van der Waals heterostructures are investigated by first-principles calculations. The g-C2N/MoSe2 heterostructure is an indirect band gap semiconductor at a strain from 0% to 8%, where its band gap is 0.66, 0.61, 0.73, 0.60 and 0.33 eV. At K point, the spin splitting is 186, 181, 39, 13 and 9 meV, respectively. For g-C2N/WSe2 heterostructures, the band gap is 0.32, 0.37, 0.42, 0.45 and 0.36 eV, and the conduction band minimum is shifted from Г-M region to K-Г region as the strain increases from 0% to 8%. Its spin splitting monotonically decreases as a strain raises to 8%, which is 445, 424, 261, 111 and 96 meV, respectively. Moreover, at a strain less than 4%, the conduction band mainly comes from g-C2N, but it comes from XSe2 (X=Mo, W) above 6%. Our results show that the g-C2N/XSe2 heterostructures have tunable electronic structures, which makes it a potential candidate for novel electronic devices.

  8. Influence of Pretreatment Conditions on Methane Aromatization Performance of Mo/HZSM-5 and Mo-Cu/HZSM-5 Catalysts

    Institute of Scientific and Technical Information of China (English)

    Yiping Zhang; Dongjie Wang; Jinhua Fei; Xiaoming Zheng

    2003-01-01

    Mo/HZSM-5 is a good catalyst for methane aromatization, and the reaction performance of Mo/HZSM-5 and Cu modified Mo/HZSM-5 catalysts under various pretreatment conditions has been studied. The results indicate that the catalyst presented a distinguished catalytic activity, benzene selectivity and a high stability when the bed temperature was raised in N2 atmosphere.

  9. Development of CaMoO4 crystal scintillators for double beta decay experiment with 100-Mo

    CERN Document Server

    Annenkov, A N; Danevich, F A; Georgadze, A S; Kim, S K; Kim, H J; Kim, Y D; Kobychev, V V; Kornoukhov, V N; Korzhik, M; Lee, J I; Missevitch, O; Mokina, V M; Nagorny, S S; Nikolaiko, A S; Poda, D V; Podviyanuk, R B; Sedlak, D J; Shkulkova, O G; So, J H; Solsky, I M; Tretyak, V I; Yurchenko, S S

    2007-01-01

    Energy resolution, alpha/beta ratio, pulse-shape discrimination for gamma rays and alpha particles, temperature dependence of scintillation properties, and radioactive contamination were studied with CaMoO4 crystal scintillators. A high sensitivity experiment to search for neutrinoless double beta decay of 100-Mo by using CaMoO4 scintillators is discussed.

  10. A trinuclear Mo-Fe-Mo cluster compound [ Et4N] {[Me2dtcMoO(μ-S) 2] 2Fe} containing dialkyldithiocarbamate ligand

    Institute of Scientific and Technical Information of China (English)

    ZHANG, Yan-Shi; LIU, Qiu-Tian; ZHU, Hong-Ping; CHEN, Yi-Hui; CHEN, Chang-Neng

    2000-01-01

    A trinuclear linear Mo-Fe-Mo dialkyldithiocarbamate complex [Et4N] {[Me2dtcMoO(μ-S)2]2Fe} has been obtained and structurally characterized, which contains two Me2dtcMoO(μ-S)2 units coordinated to a central tetrahedral Fe atom. A comparison of the structural parameters indicates the metal oxidation states of 2Mo(v) + Fe(Ⅲ). The 1H NMR shows chemical shifts of Me2dtc ligands at δ 10.14 and δ 9.40 with the intensity ratio of 1:1. The cyclic voltammogram displays a reversiible couple at - 1.41 V/- 1.36 V responsible for 1-/2-anions of the complex and an irreversible oxidation at 0.5 V,which seems to show the apparent lack of stability for its neutral species (Me2dtcMoOS2)2Fe.

  11. Valence-band offsets and Schottky barrier heights of layered semiconductors explained by interface-induced gap states

    Science.gov (United States)

    Mönch, Winfried

    1998-04-01

    Many metal chalcogenides are layered semiconductors. They consist of chalcogen-metal-chalcogen layers that are themselves bound by van der Waals forces. Hence, heterostructures involving layered compounds are abrupt and strain-free. Experimental valence-band offsets of heterostructures between GaSe, InSe, SnS2, SnSe2, MoS2, MoTe2, WSe2, and CuInSe2 and between some of these compounds and ZnSe, CdS, and CdTe as well as barrier heights of Au contacts on GaSe, InSe, MoS2, MoTe2, WSe2, ZnSe, CdS, and CdTe are analyzed. The valence-band discontinuities of the heterostructures and the barrier heights of the Schottky contact compounds are consistently described by the continuum of interface-induced gap states as the primary mechanism that governs the band lineup at semiconductor interfaces.

  12. Comparison of lithographic performance between MoSi binary mask and MoSi attenuated PSM

    Science.gov (United States)

    Yamana, Mitsuharu; Lamantia, Matthew; Philipsen, Vicky; Wada, Shingo; Nagatomo, Tatsuya; Tonooka, Yoji

    2009-04-01

    The mask error budget continues to shrink with shrinking DRAM half pitch and MPU gate size year by year. The ITRS roadmap calls for mask CDU to be cut in half by 2014[1]. Both mask maker and mask user must take advantage of various mask properties, OPC strategies and resolution enhancement techniques to drive improvements. Mask material selection impacts both lithographic performance and mask manufacturability. In turn mask material properties and manufacturing techniques impact our ability to meet the technology roadmap. Studies have shown the advantages of polarized light[2,3] as well as the impact of various mask materials on high NA lithography[4]. In this paper we select the recently introduced binary mask material made from a MoSi absorber called Opaque MoSi On Glass (OMOG) for comparison with the conventional 6% att. PSM and 20% att. MoSi PSM. Through simulation and wafer prints, we optimized mask feature from viewpoint of MEEF and maximum exposure latitude (EL). The MoSi att. PSMs suffer from higher MEEF, which is attributed to the negative effect of TE polarization for mask duty cycle of 50% for 50 nm half pitch and below. Therefore a lower mask duty cycle is required for att. PSM to bring the MEEF performance back to acceptable levels. Experimental results confirm simulation results. As a result of the lower mask duty cycle, the att. MoSi PSMs exhibit poor Sub Resolution Assist Feature (SRAF) printability. On the contrary, the MoSi binary mask delivers both acceptable MEEF and acceptable SRAF printing performance. Moreover, we found that the mask structure impact of OMOG to wafer CD is smallest among three masks. OMOG gives the best combination of lithographic performance and delivery compared to the MoSi att. PSMs.

  13. Level studies of 93Mo via 93Nb(p, nγ93Mo reaction and density of discrete levels in 93Mo

    Directory of Open Access Journals (Sweden)

    Razavi Rohallah

    2011-01-01

    Full Text Available The excited states of 93Mo have been investigated via the 93Nb(P,nγ93Mo reaction with proton beam energies of 2.5-4.3 MeV. The parameters of the nuclear level density formula were determined from the extensive and complete level scheme of 93Mo. The Bethe formula for the back-shifted Fermi gas model and the constant temperature model are compared with experimental level densities.

  14. Single-Band and Dual-Band Infrared Detectors

    Science.gov (United States)

    Ting, David Z. (Inventor); Gunapala, Sarath D. (Inventor); Soibel, Alexander (Inventor); Nguyen, Jean (Inventor); Khoshakhlagh, Arezou (Inventor)

    2017-01-01

    Bias-switchable dual-band infrared detectors and methods of manufacturing such detectors are provided. The infrared detectors are based on a back-to-back heterojunction diode design, where the detector structure consists of, sequentially, a top contact layer, a unipolar hole barrier layer, an absorber layer, a unipolar electron barrier, a second absorber, a second unipolar hole barrier, and a bottom contact layer. In addition, by substantially reducing the width of one of the absorber layers, a single-band infrared detector can also be formed.

  15. Metallic MoO₂ cocatalyst significantly enhances visible-light photocatalytic hydrogen production over Mo₂/Zn₀.₅Cd₀.₅S heterojunction.

    Science.gov (United States)

    Du, Hong; Xie, Xiao; Zhu, Qing; Lin, Ling; Jiang, Yi-Fan; Yang, Zheng-Kun; Zhou, Xiao; Xu, An-Wu

    2015-03-19

    As semiconductor-based nanoheterostructures play a decisive role in current electronics and optoelectronics, the introduction of active heterojunctions can afford new and improved capabilities that will enhance the conversion of solar energy into chemical energy. In this work, a novel metal/semiconductor MoO₂/Zn₀.₅Cd₀.₅S heterojunction has been designed and prepared to significantly enhance photocatalytic H₂ production efficiency. The photocatalytic activity of the as-prepared MoO₂/Zn₀.₅Cd₀.₅S for H₂ generation from water under visible-light irradiation (λ ≥ 420 nm) is measured. MoO₂/Zn₀.₅Cd₀.₅S hybrid nanoparticles have a higher photocatalytic activity than Zn₀.₅Cd₀.₅S even without the noble metal cocatalyst. The results show that the rate of H₂ evolution over annealed MoO₂/Zn₀.₅Cd₀.₅S is about 13 times higher than that of Zn₀.₅Cd₀.₅S alone, and 10 times higher than that of simply mixed MoO₂/Zn₀.₅Cd₀.₅S. Implying that the strong coupling at the interface of MoO₂ and Zn₀.₅Cd₀.₅S facilitates electron transfer from the conduction band of Zn₀.₅Cd₀.₅S to metallic MoO₂, thus promoting the separation of photogenerated electrons and holes. MoO₂ (2 wt%)/Zn₀.₅Cd₀.₅S heterostructured photocatalyst calcined at 673 K achieves the optimal overall activity for H₂ evolution. The introduction of metallic MoO₂ cocatalyst leads to a remarkable improvement in the photo current and photocatalytic H₂ production activity of Zn₀.₅Cd₀.₅S, and the content of MoO₂ in this catalyst has an important influence on the photocatalytic activity. It is shown that 2 wt% metallic MoO₂ loaded on Zn₀.₅Cd₀.₅S sample produces a maximum photocatalytic H₂ production rate of 252.4 μmol h(-1). The junctions formed between metallic MoO₂ and semiconductor Zn₀.₅Cd₀.₅S by calcination play a key role in high photocatalytic water splitting to produce H₂. Our study

  16. Formation of Silicide Coating layer on U-Mo Powder

    Energy Technology Data Exchange (ETDEWEB)

    Nam, Ji Min; Kim, Sunghwan; Lee, Kyu Hong [Korea Atomic Energy Research Institute, Daejeon (Korea, Republic of)

    2014-05-15

    High-density U-Mo alloys are regarded as promising candidates for advanced research reactor fuel as they have shown stable irradiation performance when compared to other uranium alloys and compounds. However, interaction layer formation between the U-Mo alloys and Al matrix degrades the irradiation performance of U-Mo Dispersion fuel. Therefore, the addition of Ti in U-Mo alloys, the addition of Si in a Al matrix, and silicide or nitride coating on the surface of U-Mo particles have been proposed to inhibit the interaction layer growth. In this study, U-Mo alloy powder was produced using a centrifugal atomization method. In addition, silicide coating layers were fabricated by several mixing process changes on the surface of the U-Mo particles. The coated powders were characterized by using scanning electron microscopy (SEM) and energy dispersive x-ray spectroscopy (EDAX). Decreased annealing duration did not affect the forming of silicide coating layers on the surface of U-7wt%Mo powders. The variation in the mixing ratio between U-7wt%Mo and Si powders had an effect on the quality of silicide coating on the U-7wt%Mo powders. The weight of Si powders should be smaller than that of U-7wt%Mo powders for better silicide coating when it comes to the mixing ratio.

  17. Adhesives for fixed orthodontic bands.

    Science.gov (United States)

    Millett, Declan T; Glenny, Anne-Marie; Mattick, Rye Cr; Hickman, Joy; Mandall, Nicky A

    2016-10-25

    Orthodontic treatment involves using fixed or removable appliances (dental braces) to correct the positions of teeth. It has been shown that the quality of treatment result obtained with fixed appliances is much better than with removable appliances. Fixed appliances are, therefore, favoured by most orthodontists for treatment. The success of a fixed orthodontic appliance depends on the metal attachments (brackets and bands) being attached securely to the teeth so that they do not become loose during treatment. Brackets are usually attached to the front and side teeth, whereas bands (metal rings that go round the teeth) are more commonly used on the back teeth (molars). A number of adhesives are available to attach bands to teeth and it is important to understand which group of adhesives bond most reliably, as well as reducing or preventing dental decay during the treatment period. To evaluate the effectiveness of the adhesives used to attach bands to teeth during fixed appliance treatment, in terms of:(1) how often the bands come off during treatment; and(2) whether they protect the banded teeth against decay during fixed appliance treatment. The following electronic databases were searched: Cochrane Oral Health's Trials Register (searched 2 June 2016), Cochrane Central Register of Controlled Trials (CENTRAL; 2016, Issue 5) in the Cochrane Library (searched 2 June 2016), MEDLINE Ovid (1946 to 2 June 2016) and EMBASE Ovid (1980 to 2 June 2016). We searched ClinicalTrials.gov and the World Health Organization International Clinical Trials Registry Platform for ongoing trials. No restrictions were placed on the language or date of publication when searching the electronic databases. Randomised and controlled clinical trials (RCTs and CCTs) (including split-mouth studies) of adhesives used to attach orthodontic bands to molar teeth were selected. Patients with full arch fixed orthodontic appliance(s) who had bands attached to molars were included. All review authors

  18. Correlations in a Band Insulator

    Science.gov (United States)

    Sentef, Michael; Kunes, Jan; Kampf, Arno P.; Werner, Philipp

    2010-03-01

    Using DMFT we find a discontinuous band-to-Mott insulator transition upon an increase in the local Coulomb repulsion in a covalent band insulator [1,2], defined as a band insulator with partially filled local orbitals. The corresponding band gap is a hybridization gap arising from a particular pattern of hopping integrals. Similar characteristics apply to materials such as FeSi, FeSb2 or CoTiSb [3], some of which exhibit temperature dependent magnetic and transport properties reminiscent of Kondo insulators. Both charge and spin gaps in the covalent band insulator shrink with increasing Coulomb repulsion. At moderate interaction strengths the gap renormalization is well described by a renormalization factor analogous to the quasiparticle weight in a Fermi liquid. [4pt] [1] M. Sentef, J. Kunes, P. Werner, and A.P. Kampf, Phys. Rev. B 80, 155116 (2009) [0pt] [2] A.P. Kampf, M. Kollar, J. Kunes, M. Sentef, and D. Vollhardt, arXiv:0910.5126

  19. William Band at Yenching University

    Science.gov (United States)

    Hu, Danian

    2008-04-01

    William Band (1906-1993) has been widely remembered by his American colleagues and students as ``a fine physicist and teacher,'' who taught at Washington State University in Pullman between 1949 and 1971 and authored Introduction to Quantum Statistics (1954) and Introduction to Mathematical Physics (1959). Not many, however, knew much about Band's early career, which was very ``uncommon and eventful.'' Born in England, Band graduated from University of Liverpool in 1927 with an MsSc degree in physics. Instead of pursuing his Ph.D. at Cambridge, he chose to teach physics at Yenching University, a prestigious Christian university in Beijing, China. Arriving in 1929, Band established his career at Yenching, where he taught and researched the theory of relativity and quantum mechanics, pioneered the study on low-temperature superconductivity in China, founded the country's first graduate program in physics, and chaired the Physics Department for 10 years until he fled from Yenching upon hearing of the attack on Pearl Harbor. It took him two years to cross Japanese occupied areas under the escort of the Communist force; he left China in early 1945. This presentation will explore Band's motivation to work in China and his contributions to the Chinese physics research and education.

  20. Optical properties of a new Bi38Mo7O78 semiconductor with fluorite-type δ-Bi2O3 structure

    Science.gov (United States)

    Wang, Zuoshan; Bi, Shala; Wan, Yingpeng; Huang, Pengjie; Zheng, Min

    2017-03-01

    Bi3+-containing inorganic materials usually show rich optical and electronic properties due to the hybridization between 6s and 6p electronic components together with the lone pair in Bi3+ ions. In this work, a new semiconductor of bismuth molybdate Bi38Mo7O78 (19Bi2O3·7MoO3) was synthesized by the sol-gel film coating and the following heat process. The samples developed into nanoparticles with average size of 40 nm. The phase formation was verified via the XRD Rietveld structural refinement. Orthorhombic Bi38Mo7O78 can be regarded to be derived from the cubic δ-phase Bi2O3 structure. The microstructure was investigated by SEM, EDX, TEM, BET and XPS measurements. The UV-vis absorption spectra showed that the band gap of Bi38Mo7O78 (2.38 eV) was greatly narrowed in comparison with Bi2O3 (2.6 eV). This enhances the efficient absorption of visible light. Meanwhile, the conduction band of is wider and shows more dispersion, which greatly benefits the mobility of the light-induced charges taking part in the photocatalytic reactions. Bi38Mo7O78 nanoparticles possess efficient activities on the photodegradation of methylene blue (MB) solutions under the excitation of visible-light. The photocatalysis activities and mechanisms were discussed on the crystal structure characteristics and the measurements such as photoluminescence, exciton lifetime and XPS results.

  1. Order-disorder phase transitions in the two-dimensional semiconducting transition metal dichalcogenide alloys Mo1−xWxX2 (X = S, Se, and Te)

    KAUST Repository

    Gan, Liyong

    2014-10-21

    A combination of density functional theory, an empirical model, and Monte Carlo simulations is used to shed light on the evolution of the atomic distribution in the two-dimensional semiconducting transition metal dichalcogenide alloys Mo1−xWxX2 (X = S, Se, and Te) as a function of the W concentration and temperature. Both random and ordered phases are discovered and the origin of the phase transitions is clarified. While the empirical model predicts at x = 1/3 and 2/3 ordered alloys, Monte Carlo simulations suggest that they only exist at low temperature due to a small energetic preference of Mo-X-W over Mo-X-Mo and W-X-W interactions, explaining the experimental observation of random alloy Mo1−xWxS2. Negative formation energies point to a high miscibility. Tunability of the band edges and band gaps by alteration of the W concentration gives rise to a broad range of applications.

  2. Rich structural phase diagram and thermoelectric properties of layered tellurides Mo{sub 1−x}Nb{sub x}Te{sub 2}

    Energy Technology Data Exchange (ETDEWEB)

    Ikeura, Koji; Sakai, Hideaki [Department of Applied Physics, University of Tokyo, Hongo, Tokyo 113-8656 (Japan); Bahramy, Mohammad Saeed [Department of Applied Physics, University of Tokyo, Hongo, Tokyo 113-8656 (Japan); RIKEN Center for Emergent Matter Science (CEMS), Wako, Saitama 351-0198 (Japan); Ishiwata, Shintaro, E-mail: ishiwata@ap.t.u-tokyo.ac.jp [Department of Applied Physics, University of Tokyo, Hongo, Tokyo 113-8656 (Japan); JST, PRESTO, Kawaguchi, Saitama 332-0012 (Japan)

    2015-04-01

    MoTe{sub 2} is a rare transition-metal ditelluride having two kinds of layered polytypes, hexagonal structure with trigonal prismatic Mo coordination and monoclinic structure with octahedral Mo coordination. The monoclinic distortion in the latter is caused by anisotropic metal-metal bonding. In this work, we have examined the Nb doping effect on both polytypes of MoTe{sub 2} and clarified a structural phase diagram for Mo{sub 1−x}Nb{sub x}Te{sub 2} containing four kinds of polytypes. A rhombohedral polytype crystallizing in polar space group has been newly identified as a high-temperature metastable phase at slightly Nb-rich composition. Considering the results of thermoelectric measurements and the first-principles calculations, the Nb ion seemingly acts as a hole dopant in the rigid band scheme. On the other hand, the significant interlayer contraction upon the Nb doping, associated with the Te p-p hybridization, is confirmed especially for the monoclinic phase, which implies a shift of the p-band energy level. The origin of the metal-metal bonding in the monoclinic structure is discussed in terms of the d electron counting and the Te p-p hybridization.

  3. Atomic-Scale Spectroscopy of Gated Monolayer MoS2.

    Science.gov (United States)

    Zhou, Xiaodong; Kang, Kibum; Xie, Saien; Dadgar, Ali; Monahan, Nicholas R; Zhu, X-Y; Park, Jiwoong; Pasupathy, Abhay N

    2016-05-11

    The electronic properties of semiconducting monolayer transition-metal dichalcogenides can be tuned by electrostatic gate potentials. Here we report gate-tunable imaging and spectroscopy of monolayer MoS2 by atomic-resolution scanning tunneling microscopy/spectroscopy (STM/STS). Our measurements are performed on large-area samples grown by metal-organic chemical vapor deposition (MOCVD) techniques on a silicon oxide substrate. Topographic measurements of defect density indicate a sample quality comparable to single-crystal MoS2. From gate voltage dependent spectroscopic measurements, we determine that in-gap states exist in or near the MoS2 film at a density of 1.3 × 10(12) eV(-1) cm(-2). By combining the single-particle band gap measured by STS with optical measurements, we estimate an exciton binding energy of 230 meV on this substrate, in qualitative agreement with numerical simulation. Grain boundaries are observed in these polycrystalline samples, which are seen to not have strong electronic signatures in STM imaging.

  4. Direct Growth of MoS₂/h-BN Heterostructures via a Sulfide-Resistant Alloy.

    Science.gov (United States)

    Fu, Lei; Sun, Yangyong; Wu, Nian; Mendes, Rafael G; Chen, Linfeng; Xu, Zhen; Zhang, Tao; Rümmeli, Mark H; Rellinghaus, Bernd; Pohl, Darius; Zhuang, Lin; Fu, Lei

    2016-02-23

    Improved properties arise in transition metal dichalcogenide (TMDC) materials when they are stacked onto insulating hexagonal boron nitride (h-BN). Therefore, the scalable fabrication of TMDCs/h-BN heterostructures by direct chemical vapor deposition (CVD) growth is highly desirable. Unfortunately, to achieve this experimentally is challenging. Ideal substrates for h-BN growth, such as Ni, become sulfides during the synthesis process. This leads to the decomposition of the pregrown h-BN film, and thus no TMDCs/h-BN heterostructure forms. Here, we report a thoroughly direct CVD approach to obtain TMDCs/h-BN vertical heterostructures without any intermediate transfer steps. This is attributed to the use of a nickel-based alloy with excellent sulfide-resistant properties and a high catalytic activity for h-BN growth. The strategy enables the direct growth of single-crystal MoS2 grains of up to 200 μm(2) on h-BN, which is approximately 1 order of magnitude larger than that in previous reports. The direct band gap of our grown single-layer MoS2 on h-BN is 1.85 eV, which is quite close to that for free-standing exfoliated equivalents. This strategy is not limited to MoS2-based heterostructures and so allows the fabrication of a variety of TMDCs/h-BN heterostructures, suggesting the technique has promise for nanoelectronics and optoelectronic applications.

  5. Deoxygenation of glycolaldehyde and furfural on Mo2C/Mo(100)

    Science.gov (United States)

    McManus, Jesse R.; Vohs, John M.

    2014-12-01

    The desire to produce fuels and chemicals in an energy conscious, environmentally sympathetic approach has motivated considerable research on the use of cellulosic biomass feedstocks. One of the major challenges facing the utilization of biomass is finding effective catalysts for the efficient and selective removal of oxygen from the highly-oxygenated, biomass-derived platform molecules. Herein, a study of the reaction pathways for the biomass-derived platform molecule furfural and biomass-derived sugar model compound glycolaldehyde provides insight into the mechanisms of hydrodeoxygenation (HDO) on a model molybdenum carbide catalyst, Mo2C/Mo(100). Using temperature programmed desorption (TPD) and high resolution electron energy loss spectroscopy (HREELS), it was found that the Mo2C/Mo(100) catalyst was active for selective deoxygenation of the aldehyde carbonyl by facilitating adsorption of the aldehyde in an η2(C,O) bonding configuration. Furthermore, the catalyst showed no appreciable activity for furanic ring hydrogenation, highlighting the promise of relatively inexpensive Mo2C catalysts for selective HDO chemistry.

  6. Linear methods in band theory

    DEFF Research Database (Denmark)

    Andersen, O. Krogh

    1975-01-01

    and they specify the boundary conditions on a single MT or atomic sphere in the most convenient way. This method is very well suited for self-consistent calculations. The empty-lattice test is applied to the linear-MTO method and the free-electron energy bands are accurately reproduced. Finally, it is shown how......Two approximate methods for solving the band-structure problem in an efficient and physically transparent way are presented and discussed in detail. The variational principle for the one-electron Hamiltonian is used in both schemes, and the trial functions are linear combinations of energy......-independent augmented plane waves (APW) and muffin-tin orbitals (MTO), respectively. The secular equations are therefore eigenvalue equations, linear in energy. The trial functions are defined with respect to a muffin-tin (MT) potential and the energy bands depend on the potential in the spheres through potential...

  7. X-Band PLL Synthesizer

    Directory of Open Access Journals (Sweden)

    P. Kutin

    2006-04-01

    Full Text Available This paper deals with design and realization of a PLL synthesizer for the microwave X−band. The synthesizer is intended for use as a local oscillator in a K−band downconverter. The design goal was to achieve very low phase noise and spurious free signal with a sufficient power level. For that purpose a low phase noise MMIC VCO was used in phase locked loop. The PLL works at half the output frequency, therefore there is a frequency doubler at the output of the PLL. The output signal from the frequency doubler is filtered by a band-pass filter and finally amplified by a single stage amplifier.

  8. Electronic Structure of the ID Conductor K0.3MoO3 studied using resonant inelastic x-ray scattering and soft x-ray emission spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Learmonth, T.; Glans, P.-A.; McGuinness, C.; Plucinski, L.; Zhang, Y.; Guo, J.-H.; Greenblatt, M.; Smith, K.E.

    2008-09-24

    The electronic structure of the quasi-one dimensional conductor K{sub 0.3}MoO{sub 3} has been measured using high resolution resonant inelastic x-ray scattering and x-ray absorption spectroscopy. The data is compared to that from the related two dimensional insulator {alpha}-MoO{sub 3}. Scattering features are observed from both oxides that are explained in terms of the band momentum selectivity of the scattering process, allowing a comparison of the scattering data to recent band structure calculations.

  9. Low-temperature specific heat of the superconductor Mo{sub 3}Sb{sub 7}

    Energy Technology Data Exchange (ETDEWEB)

    Tran, V.H. [W. Trzebiatowski Institute of Low Temperature and Structure Research, Polish Academy of Sciences, PO Box 1410, 50-950 Wroclaw (Poland)], E-mail: v.h.tran@int.pan.wroc.pl; Miller, W. [W. Trzebiatowski Institute of Low Temperature and Structure Research, Polish Academy of Sciences, PO Box 1410, 50-950 Wroclaw (Poland); Bukowski, Z. [Laboratory for Solid State Physics, ETH Zuerich, 8093 Zuerich (Switzerland)

    2008-11-15

    The low-temperature specific heat of a superconductor Mo{sub 3}Sb{sub 7} with T{sub c} = 2.2 {+-} 0.05 K has been measured in magnetic fields up to 5 T. In the normal state, the electronic specific heat coefficient {gamma}{sub n}, and the Debye temperature {theta}{sub D} are found to be 34.5(2) mJ mol{sup -1} K{sup -2} and 283(5) K, respectively. The enhanced {gamma}{sub n} value is interpreted as due to a narrow Mo-4d band pinned at the Fermi level. The electronic specific heat in the superconducting state can be analyzed in terms a phenomenological two BCS-like gap model with the gap widths 2{delta}{sub 1}/k{sub B}T{sub c} = 4.0 and 2{delta}{sub 2}/k{sub B}T{sub c} = 2.5, and relative weights of the molar electronic heat coefficients {gamma}{sub 1}/{gamma}{sub n} = 0.7 and {gamma}{sub 2}/{gamma}{sub n} = 0.3. Some characteristic thermodynamic parameters for the studied superconductor, like the specific heat jump at T{sub c}, {delta}C(T{sub c})/{gamma}{sub n}T{sub c}, the electron-phonon coupling constant, {lambda}{sub e-ph}, the upper H{sub c2} and thermodynamic critical H{sub c0} fields, the penetration depth {lambda}, coherence length {xi} and the Ginzburg-Landau parameter {kappa} are evaluated. The estimated values of parameters such as 2{delta}{sub 0}/k{sub B}T{sub c}, {delta}C(T{sub c})/{gamma}{sub n}T{sub c}, N(E{sub F}) and {lambda}{sub e-ph} suggest that Mo{sub 3}Sb{sub 7} belongs to an intermediate-coupling regime. The electronic band structure calculations indicate that the density of states near the Fermi level is formed mainly by the Mo-4d orbitals and that there is no overlap between the Mo-4d and Sb-sp orbitals.

  10. Atomically thin arsenene and antimonene: semimetal-semiconductor and indirect-direct band-gap transitions.

    Science.gov (United States)

    Zhang, Shengli; Yan, Zhong; Li, Yafei; Chen, Zhongfang; Zeng, Haibo

    2015-03-01

    The typical two-dimensional (2D) semiconductors MoS2, MoSe2, WS2, WSe2 and black phosphorus have garnered tremendous interest for their unique electronic, optical, and chemical properties. However, all 2D semiconductors reported thus far feature band gaps that are smaller than 2.0 eV, which has greatly restricted their applications, especially in optoelectronic devices with photoresponse in the blue and UV range. Novel 2D mono-elemental semiconductors, namely monolayered arsenene and antimonene, with wide band gaps and high stability were now developed based on first-principles calculations. Interestingly, although As and Sb are typically semimetals in the bulk, they are transformed into indirect semiconductors with band gaps of 2.49 and 2.28 eV when thinned to one atomic layer. Significantly, under small biaxial strain, these materials were transformed from indirect into direct band-gap semiconductors. Such dramatic changes in the electronic structure could pave the way for transistors with high on/off ratios, optoelectronic devices working under blue or UV light, and mechanical sensors based on new 2D crystals.

  11. Holographic Multi-Band Superconductor

    CERN Document Server

    Huang, Ching-Yu; Maity, Debaprasad

    2011-01-01

    We propose a gravity dual for the holographic superconductor with multi-band carriers. Moreover, the currents of these carriers are unified under a global non-Abelian symmetry, which is dual to the bulk non-Abelian gauge symmetry. We study the phase diagram of our model, and find it qualitatively agrees with the one for the realistic 2-band superconductor, such as MgB2. We also evaluate the holographic conductivities and find the expected mean-field like behaviors in some cases. However, for a wide range of the parameter space, we also find the non-mean-field like behavior with negative conductivities.

  12. Analysis of superdeformed rotational bands

    Science.gov (United States)

    Lalazissis, G. A.; Hara, K.

    1998-07-01

    Available experimental data for the ΔI=2 transition energies in superdeformed bands are analyzed by using an extended one-point formula. The existence of deviations from the smooth behavior is confirmed in many bands. However, we stress that one cannot necessarily speak about regular staggering patterns as they are mostly irregular. We present a simulation of the experimental data in terms of a simple model, which suggests that the irregularities may stem from the presence of irregular kinks in the rotational spectrum. However, at present, where such kinks may come from is an open question.

  13. X-Band PLL Synthesizer

    OpenAIRE

    P. Kutin; Vagner, P.

    2006-01-01

    This paper deals with design and realization of a PLL synthesizer for the microwave X−band. The synthesizer is intended for use as a local oscillator in a K−band downconverter. The design goal was to achieve very low phase noise and spurious free signal with a sufficient power level. For that purpose a low phase noise MMIC VCO was used in phase locked loop. The PLL works at half the output frequency, therefore there is a frequency doubler at the output of the PLL. The output signal ...

  14. Synthesis of α-MoO{sub 3} nanoplates using organic aliphatic acids and investigation of sunlight enhanced photodegradation of organic dyes

    Energy Technology Data Exchange (ETDEWEB)

    Kumar, V. Vinod; Gayathri, K.; Anthony, Savarimuthu Philip, E-mail: philip@biotech.sastra.edu

    2016-04-15

    Graphical abstract: Thermodynamically stable α-MoO{sub 3} nanoplates and nanorods were synthesized using organic structure controlling agents and demonstrated sun light enhanced photocatalytic degradation of methylene blue (MB) and rhodamine blue (Rh-B) dyes in aqueous solution. - Highlights: • α-MoO{sub 3} hexagonal nanoplates using organic structure controlling agents. • Tunable optical band gap of MoO{sub 3}. • Demonstrated strong sun light mediated enhanced photodegradation of methylene blue and rhodamine blue. • Photodegradation did not use any other external oxidizing agents. - Abstract: Thermodynamically stable α-MoO{sub 3} nanoplates were synthesized using organic aliphatic acids as structure controlling agents and investigated photocatalytic degradation of methylene blue (MB) and rhodamine blue (Rh-B) in presence of sun light. Three different organic aliphatic acids, citric acid (CA), tartaric acid (TA) and ethylene diamine tetra-acetic acid (EDTA), were employed to control morphologies. CA and TA predominantly produced extended hexagonal plates where EDTA gave nanorods as well as nanoplates. PXRD studies confirmed the formation of α-MoO{sub 3} nanoparticles. HR-TEM and FE-SEM reveal the formation of plate morphologies with 20–40 nm thickness, 50–100 nm diameter and 600 nm lengths. The different morphologies of α-MoO{sub 3} nanoparticles lead to the tunable optical band gap between 2.80 and 2.98 eV which was obtained from diffused reflectance spectra (DRS). Interestingly, the synthesized α-MoO{sub 3} nanoplates exhibited strong photocatalytic degradation of MB and Rh-B up to 99% in presence of sun light without using any oxidizing agents.

  15. Transport properties of chemically synthesized MoS2 - Dielectric effects and defects scattering

    Science.gov (United States)

    Mongillo, Massimo; Chiappe, Daniele; Arutchelvan, Goutham; Asselberghs, Inge; Perucchini, Marta; Manfrini, Mauricio; Lin, Dennis; Huyghebaert, Cedric; Radu, Iuliana

    2016-12-01

    We report on the electrical characterization of synthetic, large-area MoS2 layers obtained by the sulfurization technique. The effects of dielectric encapsulation and localized defect states on the intrinsic transport properties are explored with the aid of temperature-dependent measurements. We study the effect of dielectric environment by transferring as-grown MoS2 films into different dielectrics such as SiO2, Al2O3, HfO2, and ZrO2 with increasing dielectric permittivity. Electrical data are collected on a statistically-relevant device ensemble and allow to assess device performances on a large scale assembly. Our devices show relative in-sensitiveness of mobility with respect to dielectric encapsulation. We conclude that the device behavior is strongly affected by several scattering mechanisms of different origin that can completely mask any effect related to dielectric mismatch. At low temperatures, conductivity of the devices is thermally activated, a clear footprint of the existence of a mobility edge separating extended states in the conduction band from impurity states in the band-gap.

  16. Upconversion emission study of Er3+ doped CaMoO4 phosphor

    Science.gov (United States)

    Sinha, Shriya; Mahata, Manoj Kumar; Rai, V. K.; Kumar, Kaushal

    2016-05-01

    The infrared to visible upconversion emission in Er3+ doped CaMoO4 phosphor has been investigated upon 980 nm diode laser excitation. The X-ray dffraction analysis reveals well crystalline nature and tetragonal phase structure of the prepared phosphor annealed at 800 °C. The Er3+ doped CaMoO4 phosphor has shown intense green upconversion emission upon 980 nm didode laser excitation. The green emission bands at 530 nm and 552 nm corresponds to the 2H11/2→4I15/2 and 4S3/2→4I15/2 electronic transitions, respectively of Er3+ ion. The very weak red emission band around 656 nm is assigned to the 4F9/2→4I15/2 transition of Er3+ ion. The CIE color coordinate exhibits the emission color in intense green region, indicating the use of present phosphor in display device applications.

  17. Tribological behavior of magnetron sputtering CrMoN/MoS2 composite coatings

    Institute of Scientific and Technical Information of China (English)

    Yuelan DI; Zhihai CAI; Ping ZHANG; Zhen YANG; Qi LI; Wei SHEN

    2012-01-01

    CrMoN composite coatings were deposited on the surface of the stainless steel by magnetron sputtering,then were treated by low temperature ion sulfuration.FESEM equipped with EDX was adopted to analyze the morphologies and compositions of the surface,cross-section and worn scar of the sulfuration layer.The valence states of the film surface were detected by XPS.The nano-hardness and nano-modulus of the layer were measured by a nano tester.The results of the friction and wear show that the CrMoN/MoS2 composite coating is a kind of ideal solid lubrication layer and possess an excellent antifriction and wear-resistance.

  18. Electroluminescence from indirect band gap semiconductor ReS2

    Science.gov (United States)

    Gutiérrez-Lezama, Ignacio; Aditya Reddy, Bojja; Ubrig, Nicolas; Morpurgo, Alberto F.

    2016-12-01

    It has been recently claimed that bulk crystals of transition metal dichalcogenide (TMD) ReS2 are direct band gap semiconductors, which would make this material an ideal candidate, among all TMDs, for the realization of efficient opto-electronic devices. The situation is however unclear, because even more recently an indirect transition in the PL spectra of this material has been detected, whose energy is smaller than the supposed direct gap. To address this issue we exploit the properties of ionic liquid gated field-effect transistors (FETs) to investigate the gap structure of bulk ReS2. Using these devices, whose high quality is demonstrated by a record high electron FET mobility of 1100 cm2 V-1 s-1 at 4 K, we can induce hole transport at the surface of the material and determine quantitatively the smallest band gap present in the material, irrespective of its direct or indirect nature. The value of the band gap is found to be 1.41 eV, smaller than the 1.5 eV direct optical transition but in good agreement with the energy of the indirect optical transition, providing an independent confirmation that bulk ReS2 is an indirect band gap semiconductor. Nevertheless, contrary to the case of more commonly studied semiconducting TMDs (e.g., MoS2, WS2, etc) in their bulk form, we also find that ReS2 FETs fabricated on bulk crystals do exhibit electroluminescence when driven in the ambipolar injection regime, likely because the difference between direct and indirect gap is only 100 meV. We conclude that ReS2 does deserve more in-depth investigations in relation to possible opto-electronic applications.

  19. Mo isotope fractionation during hydrothermal evolution of porphyry Cu systems

    Science.gov (United States)

    Shafiei, Behnam; Shamanian, GholamHossein; Mathur, Ryan; Mirnejad, Hassan

    2015-03-01

    We present Mo isotope compositions of molybdenite types from three successive stages of ore deposition in several porphyry copper deposits of the Kerman region, Iran. The data provide new insights into controlling processes on Mo isotope fractionation during the hydrothermal evolution of porphyry systems. The Mo isotope compositions of 27 molybdenite samples show wide variations in δ97Mo ranging from -0.37 to +0.92 ‰. The data reveal that molybdenites in the early and transitional stages of mineralization (preferentially 2H polytypes; δ97Mo mean = 0.35 ‰) have higher δ97Mo values than late stage (mainly 3R polytypes; δ97Mo mean = 0.02 ‰) molybdenites. This trend suggests that fractionation of Mo isotopes occurred in high-temperature stages of mineralization and that hydrothermal systems generally evolve towards precipitation of molybdenite with lower δ97Mo values. Taking into account the genetic models proposed for porphyry Cu deposits along with the temperature-dependent fractionation of Mo isotope ratios, it is proposed that large variations of Mo isotopes in the early and the transitional stages of ore deposition could be controlled by the separation of the immiscible ore-forming fluid phases with different density, pH, and ƒO2 properties (i.e., brine and vapor). The fractionation of Mo isotopes during fluid boiling and Rayleigh distillation processes likely dominates the Mo isotope budget of the remaining ore-forming fluids for the late stage of mineralization. The lower δ97Mo values in the late stage of mineralization can be explained by depletion of the late ore-forming hydrothermal solutions in 97Mo, as these fluids have moved to considerable distance from the source. Finally, the relationship observed between MoS2 polytypes (2H and 3R) and their Mo isotopic compositions can be explained by the molecular vibration theory, in which heavier isotopes are preferentially partitioned into denser primary 2H MoS2 crystals.

  20. Nanostructured Mo-based electrode materials for electrochemical energy storage.

    Science.gov (United States)

    Hu, Xianluo; Zhang, Wei; Liu, Xiaoxiao; Mei, Yueni; Huang, Yunhui

    2015-04-21

    The development of advanced energy storage devices is at the forefront of research geared towards a sustainable future. Nanostructured materials are advantageous in offering huge surface to volume ratios, favorable transport features, and attractive physicochemical properties. They have been extensively explored in various fields of energy storage and conversion. This review is focused largely on the recent progress in nanostructured Mo-based electrode materials including molybdenum oxides (MoO(x), 2 ≤ x ≤ 3), dichalconides (MoX2, X = S, Se), and oxysalts for rechargeable lithium/sodium-ion batteries, Mg batteries, and supercapacitors. Mo-based compounds including MoO2, MoO3, MoO(3-y) (0 energy storage systems because of their unique physicochemical properties, such as conductivity, mechanical and thermal stability, and cyclability. In this review, we aim to provide a systematic summary of the synthesis, modification, and electrochemical performance of nanostructured Mo-based compounds, as well as their energy storage applications in lithium/sodium-ion batteries, Mg batteries, and pseudocapacitors. The relationship between nanoarchitectures and electrochemical performances as well as the related charge-storage mechanism is discussed. Moreover, remarks on the challenges and perspectives of Mo-containing compounds for further development in electrochemical energy storage applications are proposed. This review sheds light on the sustainable development of advanced rechargeable batteries and supercapacitors with nanostructured Mo-based electrode materials.

  1. In-situ fabrication of MoSi2/SiC-Mo2C gradient anti-oxidation coating on Mo substrate and the crucial effect of Mo2C barrier layer at high temperature

    Science.gov (United States)

    Liu, Jun; Gong, Qianming; Shao, Yang; Zhuang, Daming; Liang, Ji

    2014-07-01

    MoSi2/SiC-Mo2C gradient coating on molybdenum was in situ prepared with pack cementation process by two steps: (1) carburizing with graphite powder to obtain a Mo2C layer on Mo substrate, and (2) siliconizing with Si powder to get a composite MoSi2/SiC layer on the upper part of Mo2C layer. The microstructure and elemental distribution in the coating were investigated with scanning electron microscopy (SEM), back scattered electron (BSE), energy dispersive spectroscopy (EDS), electron probe microanalysis (EPMA) and X-ray diffraction (XRD). Cyclic oxidation tests (at 500 °C, 1200 °C, 1400 °C and 1600 °C) demonstrated excellent oxidation resistance for the gradient composite coating and the mass loss was only 0.23% in 60 min at 1600 °C. XRD, EPMA, thermal dynamic and phase diagram analyses indicated that the Mo2C barrier layer played the key role in slowing down the diffusion of C and Si toward inner Mo substrate at high temperature and principally this contributed to the excellent anti-oxidation for Mo besides the outer MoSi2/SiC composite layer.

  2. In-situ fabrication of MoSi{sub 2}/SiC–Mo{sub 2}C gradient anti-oxidation coating on Mo substrate and the crucial effect of Mo{sub 2}C barrier layer at high temperature

    Energy Technology Data Exchange (ETDEWEB)

    Liu, Jun [School of Materials Science and Engineering, Tsinghua University, Beijing 100084 (China); Key Laboratory for Advanced Materials Processing Technology, Ministry of Education, Beijing 100084 (China); State Key Laboratory of New Ceramics and Fine Processing, Beijing 100084 (China); Gong, Qianming, E-mail: gongqianming@mail.tsinghua.edu.cn [School of Materials Science and Engineering, Tsinghua University, Beijing 100084 (China); Key Laboratory for Advanced Materials Processing Technology, Ministry of Education, Beijing 100084 (China); State Key Laboratory of New Ceramics and Fine Processing, Beijing 100084 (China); Shao, Yang; Zhuang, Daming [School of Materials Science and Engineering, Tsinghua University, Beijing 100084 (China); Key Laboratory for Advanced Materials Processing Technology, Ministry of Education, Beijing 100084 (China); State Key Laboratory of New Ceramics and Fine Processing, Beijing 100084 (China); Liang, Ji [Key Laboratory for Advanced Materials Processing Technology, Ministry of Education, Beijing 100084 (China); Department of Mechanical Engineering, Tsinghua University, Beijing 100084 (China)

    2014-07-01

    MoSi{sub 2}/SiC–Mo{sub 2}C gradient coating on molybdenum was in situ prepared with pack cementation process by two steps: (1) carburizing with graphite powder to obtain a Mo{sub 2}C layer on Mo substrate, and (2) siliconizing with Si powder to get a composite MoSi{sub 2}/SiC layer on the upper part of Mo{sub 2}C layer. The microstructure and elemental distribution in the coating were investigated with scanning electron microscopy (SEM), backscattered electron (BSE), energy dispersive spectroscopy (EDS), electron probe microanalysis (EPMA) and X-ray diffraction (XRD). Cyclic oxidation tests (at 500 °C, 1200 °C, 1400 °C and 1600 °C) demonstrated excellent oxidation resistance for the gradient composite coating and the mass loss was only 0.23% in 60 min at 1600 °C. XRD, EPMA, thermal dynamic and phase diagram analyses indicated that the Mo{sub 2}C barrier layer played the key role in slowing down the diffusion of C and Si toward inner Mo substrate at high temperature and principally this contributed to the excellent anti-oxidation for Mo besides the outer MoSi{sub 2}/SiC composite layer.

  3. Molybdenum Storage in Cyanobacteria: "Mopping" Up Excess Mo

    Science.gov (United States)

    Glass, J. B.; Wolfe-Simon, F.; Anbar, A. D.

    2008-12-01

    The heavy metal molybdenum (Mo) plays an essential role in the nitrogen (N) cycle. In order to acquire N from the environment, microorganisms utilize Mo-containing enzymes such as nitrogenase (for N2 fixation) and nitrate reductase (for NO3- assimilation). N2-fixing cyanobacteria likely played an important role in both marine and terrestrial N cycling throughout Earth history. Low Mo levels in Precambrian oceans may have necessitated evolution of cyanobacterial Mo-storage ("Mop") proteins. If so, mop genes were likely lost in marine cyanobacteria after the rise of Mo (to approximately 100 nanomolar (nM) 600 Ma (Scott et al., 2008)). The distribution of mop genes in N2-fixing cyanobacteria supports this hypothesis; freshwater species contain this gene whereas marine species lack it. To assess the importance of Mo-storage in modern environments we are integrating laboratory and field investigations. In the lab, we grew N2-fixing freshwater cyanobacteria possessing the mop gene at high Mo levels (1500 nM) to assess whether excess Mo is accumulated Extremely high intracellular accumulation of Mo, much higher than could be accounted for by nitrogenase requirements alone, was observed. Investigation of mop gene expression and protein localization in Mo-replete and deplete conditions is underway. In the field, we are isolating indigenous cyanobacteria and cloning mop genes from Castle Lake, California. This field locale is of particular interest because previous studies show that periphyton consortia in this lake assimilate large quantities of N, even though Mo concentrations are <5 nM. This adaptation to low Mo may be aided by intracellular Mo storage.

  4. Highly sensitive wide bandwidth photodetector based on internal photoemission in CVD grown p-type MoS2/graphene Schottky junction.

    Science.gov (United States)

    Vabbina, PhaniKiran; Choudhary, Nitin; Chowdhury, Al-Amin; Sinha, Raju; Karabiyik, Mustafa; Das, Santanu; Choi, Wonbong; Pala, Nezih

    2015-07-22

    Two dimensional (2D) Molybdenum disulfide (MoS2) has evolved as a promising material for next generation optoelectronic devices owing to its unique electrical and optical properties, such as band gap modulation, high optical absorption, and increased luminescence quantum yield. The 2D MoS2 photodetectors reported in the literature have presented low responsivity compared to silicon based photodetectors. In this study, we assembled atomically thin p-type MoS2 with graphene to form a MoS2/graphene Schottky photodetector where photo generated holes travel from graphene to MoS2 over the Schottky barrier under illumination. We found that the p-type MoS2 forms a Schottky junction with graphene with a barrier height of 139 meV, which results in high photocurrent and wide spectral range of detection with wavelength selectivity. The fabricated photodetector showed excellent photosensitivity with a maximum photo responsivity of 1.26 AW(-1) and a noise equivalent power of 7.8 × 10(-12) W/√Hz at 1440 nm.

  5. Influences of gas adsorption and Au nanoparticles on the electrical properties of CVD-grown MoS2 thin films(Conference Presentation)

    Science.gov (United States)

    Cho, Yunae; Sohn, Ahrum; Kim, Sujung; Kim, Dong-Wook; Cho, Byungjin; Hahm, Myung Gwan; Kim, Dong-Ho

    2016-10-01

    Recently, extraordinary physical properties of two-dimensional transition metal dichalcogenides (TMDs) have attracted great attention for various device applications, including photodetectors, field effect transistors, and chemical sensors. There have been intensive research efforts to grow high-quality and large area TMD thin films, and chemical vapor deposition (CVD) techniques enable scalable growth of layered MoS2 films. We investigated the roles of Au nanoparticles (NPs) on the transport and photoresponse of the CVD-grown MoS2 thin films. The Au NPs increased conductivity and enabled fast photoresponse of MoS2 thin films. These results showed that decoration of metal NPs were useful means to tailor the physical properties of CVD-grown MoS2 thin films. To clarify the roles of the metal particles, we compared the transport characteristics of MoS2 thin films with and without the Au NPs in different gas ambient conditions (N2, O2, and H2/N2). The ambient-dependence of the MoS2 thin films allowed us to discuss possible scenarios to explain our results based on considerations of band bending near the Au NPs, gas adsorption/desorption and subsequent charge transfer, and charge scattering/trapping by defect states.

  6. Novel electronic properties of a new MoS2/TiO2 heterostructure and potential applications in solar cells and photocatalysis

    Science.gov (United States)

    Li, Yanhua; Cai, Congzhong; Gu, Yonghong; Cheng, Wende; Xiong, Wen; Zhao, Chengjun

    2017-08-01

    The structural and electronic properties of two-dimensional (2D) MoS2/TiO2 heterostructure with a special configuration of Moiré pattern have been investigated for the first time using first-principles methods with van der Waals correction. It is found that the new van der Waals heterostructure is of a type-II band alignment between the MoS2 and TiO2 layers, and the electronic structures of monolayer MoS2 and 2D TiO2 are well retained in their respective layers due to a weak interlayer coupling, which suggests that the heterostructure may have potential applications in many fields such as photoelectric devices, photocatalysis, energy conversion and storage, etc. Meanwhile, the heterostructure can also provide an ideal platform of two-dimensional electron gas (2DEG) and two-dimensional hole gas (2DHG) for fundamental research such as spin Hall effect, etc. In addition, it is discovered that the corresponding MoS2/TiO2 superlattice also has similar electronic properties to MoS2/TiO2 bilayer heterostructure. Furthermore, two novel design schemes based on the MoS2/TiO2 heterostructure and superlattice are proposed for a solar cell and photocatalyst, respectively.

  7. Fabrication of 3 D Mesoporous Black TiO2 /MoS2 /TiO2 Nanosheets for Visible-Light-Driven Photocatalysis.

    Science.gov (United States)

    Liu, Xuefeng; Xing, Zipeng; Zhang, Hang; Wang, Wenmei; Zhang, Yan; Li, Zhenzi; Wu, Xiaoyan; Yu, Xiujuan; Zhou, Wei

    2016-05-23

    A novel 3 D mesoporous black TiO2 (MBT)/MoS2 /MBT sandwich-like nanosheet was successfully fabricated using a facile mechanochemical process combined with an in situ solid-state chemical reduction approach, followed by mild calcination (350 °C) under an argon atmosphere. The MBT/MoS2 /MBT exhibits a 3 D sandwich-like nanosheet structure and heterojunctions are formed at the interfaces between MoS2 and black TiO2 . The significantly narrowed band gap of MBT/MoS2 /MBT is attributed to the introduction of MoS2 and the formed Ti(3+) species in the frameworks. The visible-light photocatalytic degradation rate of methyl orange and the hydrogen production rate are as high as 89.86 % and 0.56 mmol h(-1)  g(-1) , respectively. The introduction of MoS2 and Ti(3+) in the frameworks favors the visible-light absorption and the separation of photogenerated charges, and the 3 D sandwich-like heterojunction structure facilitates the transfer of photogenerated charges.

  8. Photoinduced charge transfer involving a MoMo quadruply bonded complex to a perylene diimide.

    Science.gov (United States)

    Alberding, Brian G; Brown-Xu, Samantha E; Chisholm, Malcolm H; Epstein, Arthur J; Gustafson, Terry L; Lewis, Sharlene A; Min, Yong

    2013-04-21

    Evidence, based on femtosecond transient absorption and time resolved infrared spectroscopy, is presented for photoinduced charge transfer from the Mo2δ orbital of the quadruply bonded molecule trans-Mo2(T(i)PB)2(BTh)2, where T(i)PB = 2,4,6-triisopropyl benzoate and BTh = 2,2'-bithienylcarboxylate, to di-n-octyl perylene diimide and di-n-hexylheptyl perylene diimide in thin films and solutions of the mixtures. The films show a long-lived charge separated state while slow back electron transfer, τBET ~ 500 ps, occurs in solution.

  9. Bainite Morphology in Two Experimental Mo-Cr and Mo-Cr-V-Ti Steels

    Directory of Open Access Journals (Sweden)

    Ławrynowicz Z.

    2014-10-01

    Full Text Available The paper presents an investigation of the bainite morphology in two experimental Mo-Cr and Mo-Cr-V-Ti steels using TEM, high speed dilatometry backed by thermodynamic analysis. The microstructure was investigated using metallography and TEM method. After austenitisation at 1200oC followed by bainitic reaction in upper and lower temperatures of isothetmal transformation the bainite was in the form of classical sheaves. The amont, distribution and morphology of retained austenite and bainitic ferrite depend on prior austenitisation and isothermal transformation temperatures within the bainitic range.

  10. Grotrian diagrams for highly ionized molybdenum Mo VI through Mo XLII

    Energy Technology Data Exchange (ETDEWEB)

    Shirai, Toshizo [Japan Atomic Energy Research Inst., Tokai, Ibaraki (Japan). Tokai Research Establishment; Sugar, J.; Wiese, W.L.

    1997-07-01

    Grotrian diagrams are presented to provide graphical overviews for 1,930 spectral lines of highly ionized molybdenum, Mo VI through Mo XLII. In the usual diagram display such as that by Bashkin and Stoner (North-Holland, Amsterdam, 1975), the density of transitions is often too high to allow each transition to be drawn separately. Here in our modified diagrams, the transitions are also represented by lines connecting the upper and lower energy levels, but the lower energy levels are extended and repeated for successive configurations as needed. As a sequence, dense packing is avoided and all lines in a multiplet can be accommodated. (author)

  11. Microstructural Evolution of Rapidly Solidified Co-Mo and Ni-Mo Eutectic Alloys

    Institute of Scientific and Technical Information of China (English)

    Xiujun HAN; Wenjing YAO; Bingbo WEI

    2003-01-01

    Droplets of Co-37.6 wt pct Mo and Ni-47.7 wt pct Mo eutectic alloys were rapidly solidified during containerless processing in a 3 m drop tube. A kind of anomalous eutectic appears in these two eutectic alloys when undercooling is beyond 56 and 61 K, respectively. The two eutectic phases in anomalous eutectic were observed to grow in dendrite manner. The formation of anomalous eutectic is ascribed to the cooperative dendrite growth of the two independently nucleated eutectic phases. Current dendrite and eutectic growth theories are applied to describe the observed processes.

  12. Anti-MoS2 Nanostructures: Tl2S and Its Electrochemical and Electronic Properties.

    Science.gov (United States)

    Chia, Xinyi; Ambrosi, Adriano; Sofer, Zdeněk; Luxa, Jan; Sedmidubský, David; Pumera, Martin

    2016-01-26

    Layered transition metal dichalcogenides are catalytically important compounds. Unlike the mounting interest in transition metal dichalcogenides such as MoS2 and WS2 for electrochemical applications, other metal chalcogenides with layered structure but different chemical composition have received little attention among the scientific community. One such example is represented by thallium(I) sulfide (Tl2S), a Group 13 chalcogenide, which adopts the peculiar anti-CdCl2 type structure where the chalcogen is sandwiched between the metal layers. This is the exact opposite of a number of transition metal dichalcogenides like 1T-MoS2 adopting the regular CdCl2 structure type. The electronic structure of Tl2S thus differs from MoS2. Such structure may provide a useful insight and understanding toward its electrochemical behavior in relation to the electrochemical properties of MoS2. We thus investigated the intrinsic electroactivity of Tl2S and its implications for sensing and energy generation, specifically the electrocatalytic properties toward the hydrogen evolution reaction (HER). We show that Tl2S exhibits four distinct redox signals at ca. 0.4 V, -0.5 V, -1.0 V and -1.5 V vs Ag/AgCl as a result of its inherent cathodic and anodic processes. We also demonstrate that Tl2S possesses slow electron transfer abilities with a rate (k(0)obs) as low as 6.3 × 10(-5) cm s(-1). Tl2S displays a competent performance as a HER electrocatalyst compared to a conventional glassy carbon electrode. However, the poor conductivity of Tl2S renders the HER electrocatalytic behavior second-rate compared to MoS2. Furthermore, we investigated the electronic properties of Tl2S and found that Tl2S exhibits an unusually narrow band dispersion around the Fermi level. We show here that anti-MoS2 structure of Tl2S is accompanied by highly unusual features.

  13. Familial band-shaped keratopathy.

    Science.gov (United States)

    Ticho, U; Lahav, M; Ivry, M

    1979-01-01

    A brother and sister out of a consanguinous family of four siblings are presented as prototypes of primary band-shaped keratopathy. The disease manifested sever progressive changes of secondary nature over two years of follow-up. Histology and treatment are described.

  14. A PHOTONIC BAND GAP FIBRE

    DEFF Research Database (Denmark)

    1999-01-01

    An optical fibre having a periodicidal cladding structure provididing a photonic band gap structure with superior qualities. The periodical structure being one wherein high index areas are defined and wherein these are separated using a number of methods. One such method is the introduction...

  15. Metaphyseal bands in osteogenesis imperfecta

    Directory of Open Access Journals (Sweden)

    Suresh S

    2010-01-01

    Full Text Available An increasing number of patients with osteogenesis imperfecta are undergoing pamidronate therapy to prevent the incidence of fragility fractures. The authors herein report a child aged 3 years who received five cycles of pamidronate, resulting in metaphyseal bands, known as "zebra lines."

  16. Bands for girls and boys

    Institute of Scientific and Technical Information of China (English)

    王为成

    2001-01-01

    Like many people, you may be dreaming of a career(职业) as rock and roll stars. There are two ways to go about getting one. First is the traditional way. Find some friends and form a group. Learn to play the guitar or the drums. Write your own songs. Spend hours arguing about the band name. Then go out on the road.

  17. K-Band Latching Switches

    Science.gov (United States)

    Piotrowski, W. S.; Raue, J. E.

    1984-01-01

    Design, development, and tests are described for two single-pole-double-throw latching waveguide ferrite switches: a K-band switch in WR-42 waveguide and a Ka-band switch in WR-28 waveguide. Both switches have structurally simple junctions, mechanically interlocked without the use of bonding materials; they are impervious to the effects of thermal, shock, and vibration stresses. Ferrite material for the Ka-band switch with a proper combination of magnetic and dielectric properties was available and resulted in excellent low loss, wideband performance. The high power handling requirement of the K-band switch limited the choice of ferrite to nickel-zinc compositions with adequate magnetic properties, but with too low relative dielectric constant. The relative dielectric constant determines the junction dimensions for given frequency responses. In this case the too low value unavoidably leads to a larger than optimum junction volume, increasing the insertion loss and restricting the operating bandwidth. Efforts to overcome the materials-related difficulties through the design of a composite junction with increased effective dielectric properties efforts to modify the relative dielectric constant of nickel-zinc ferrite are examined.

  18. K-band latching switches

    Science.gov (United States)

    Piotrowski, W. S.; Raue, J. E.

    1984-05-01

    Design, development, and tests are described for two single-pole-double-throw latching waveguide ferrite switches: a K-band switch in WR-42 waveguide and a Ka-band switch in WR-28 waveguide. Both switches have structurally simple junctions, mechanically interlocked without the use of bonding materials; they are impervious to the effects of thermal, shock, and vibration stresses. Ferrite material for the Ka-band switch with a proper combination of magnetic and dielectric properties was available and resulted in excellent low loss, wideband performance. The high power handling requirement of the K-band switch limited the choice of ferrite to nickel-zinc compositions with adequate magnetic properties, but with too low relative dielectric constant. The relative dielectric constant determines the junction dimensions for given frequency responses. In this case the too low value unavoidably leads to a larger than optimum junction volume, increasing the insertion loss and restricting the operating bandwidth. Efforts to overcome the materials-related difficulties through the design of a composite junction with increased effective dielectric properties efforts to modify the relative dielectric constant of nickel-zinc ferrite are examined.

  19. Photoluminescence properties of Sm3+-doped LiY(MoO4)2 red phosphors

    Institute of Scientific and Technical Information of China (English)

    杨志平; 董宏岩; 刘鹏飞; 侯春彩; 梁晓双; 王灿; 鲁法春

    2014-01-01

    A series of novel Sm3+-doped LiY(MoO4)2 red phosphors under the UV excitation were synthesized by solid state reaction at 800 ºC for 7 h. The data measured by X-ray diffraction (XRD) indicated that the samples were all pure phases of LiY(MoO4)2. Their excitation spectra had a broad band ranging from 250 to 350 nm and several sharp peaks. The centers of the peaks were located at about 365 nm (6H5/2→4D3/2), 378 nm (6H5/2→6P7/2), 406 nm (6H5/2→4F7/2), 420 nm (6H5/2→6P5/2), 442 nm (6H5/2→4G9/2), 471 nm (6H5/2→4I13/2) and 482 nm (6H5/2→4I9/2), respectively. The strongest emission was excited by 406 nm, and the main emissions were located at 568 nm (4G5/2→6H5/2), 610 nm (4G5/2→6H7/2), 649 nm (4G5/2→6H9/2) and 710 nm (4G5/2→6H11/2). Photoluminescence prop-erties were determined for various concentrations of Sm3+-doped LiY(MoO4)2 host, and the luminescence intensity had the best value whenx=0.02 in LiY1-x(MoO4)2:xSm3+.

  20. Graphene Oxide Regulated Tin Oxide Nanostructures: Engineering Composition, Morphology, Band Structure, and Photocatalytic Properties.

    Science.gov (United States)

    Pan, Xiaoyang; Yi, Zhiguo

    2015-12-16

    A facile, one-step hydrothermal method has been developed to fabricate tin oxide-reduced graphene oxide (Sn-RGO) nanocomposites with tunable composition, morphology, and energy band structure by utilizing graphene oxide (GO) as a multifunctional two-dimensional scaffold. By adjusting the GO concentration during synthesis, a variety of tin oxide nanomaterials with diverse composition and morphology are obtained. Simultaneously, the varying of GO concentration can also narrow the bandgap and tune the band edge positions of the Sn-RGO nanocomposites. As a result, the Sn-RGO nanocomposites with controllable composition, morphology, and energy band structure are obtained, which exhibit efficient photoactivities toward methyl orange (MO) degradation under visible-light irradiation. It is expected that our work would point to the new possibility of using GO for directing synthesis of semiconductor nanomaterials with tailored structure and physicochemical properties.