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Sample records for base transition metal

  1. Preparation and magnetic properties of phthalocyanine-based carbon materials containing transition metals

    NASA Astrophysics Data System (ADS)

    Honda, Z.; Sato, S.; Hagiwara, M.; Kida, T.; Sakai, M.; Fukuda, T.; Kamata, N.

    2016-07-01

    A simple method for the preparation of bulk quantities of magnetic carbon materials, which contain uniformly dispersed transition metals (M = Fe, Co, Ni, and Cu) as the magnetic components, is presented. By using highly chlorinated metal phthalocyanine as the building block and potassium as the coupling reagent, phthalocyanine-based carbon materials (PBCMs) containing transition metals were obtained. Our experiments demonstrate the structure of these PBCMs consists of transition metals embedded in graphitic carbon that includes a square planar MN4 magnetic core and the Fe and Co-PBCM possess spontaneous magnetization at room temperature. In addition, carbon-coated transition metal particles were obtained by the Wurtz-type reaction with excess amount of potassium coupling agent. The large transition metal surface area and magnetization of these M-PBCMs are useful for spintronic and catalytic applications.

  2. Ligational behavior of Schiff bases towards transition metal ion and metalation effect on their antibacterial activity

    NASA Astrophysics Data System (ADS)

    Devi, Jai; Batra, Nisha; Malhotra, Rajesh

    2012-11-01

    New Schiff bases pyrazine-2-carboxylicacid (phenyl-pyridin-2-yl-methylene)-hydrazide (Hpch-bp) HL1 and pyrazine-2-carboxylicacid (pyridin-2-ylmethylene)-hydrazide (Hpch-pc) HL2 derived from condensation of pyrazine carboxylic hydrazide (Hpch) with 2-benzoyl pyridine (bp) or pyridine 2-carbaldehyde (pc) and their transition metal complexes of type ML(1-2)2 have been synthesized, where M = Mn(II), Co(II), Ni(II), Cu(II) and Zn(II). Characterization of ligands and their metal complexes was carried out by elemental analysis, conductimetric studies, magnetic susceptibility, spectroscopic techniques (IR, UV-VIS, NMR, ESR, Mass) and thermogravimetric analysis. The physico-chemical studies revealed octahedral geometry or distorted octahedral geometry around metal ion. These azomethine Schiff base ligands acted as tridentate ? coordinating through carbonyl, azomethine and pyridine nitrogen present in the ligand. The thermodynamic and thermal properties of the complexes have been investigated and it was observed on the basis of these studies that thermal stability of complexes follows the order Mn < Zn < Cu < Co < Ni. The ligands and their complexes were tested for in vitro antibacterial activity at different concentrations against bacteria viz. Gram positive Bacillus subtilis, Micrococcus luteus and Gram negative Pseudomonas aeruginosa, Pseudomonas mendocina. A marked enhancement in biocidal activity of the ligands under similar experimental conditions was observed as a consequence of coordination with metal ions. The trend of growth inhibition in the complexes was found to be in the order: Cu > Mn > Ni > Co > Zn.

  3. Recognition- and Reactivity-Based Fluorescent Probes for Studying Transition Metal Signaling in Living Systems

    PubMed Central

    2015-01-01

    Conspectus Metals are essential for life, playing critical roles in all aspects of the central dogma of biology (e.g., the transcription and translation of nucleic acids and synthesis of proteins). Redox-inactive alkali, alkaline earth, and transition metals such as sodium, potassium, calcium, and zinc are widely recognized as dynamic signals, whereas redox-active transition metals such as copper and iron are traditionally thought of as sequestered by protein ligands, including as static enzyme cofactors, in part because of their potential to trigger oxidative stress and damage via Fenton chemistry. Metals in biology can be broadly categorized into two pools: static and labile. In the former, proteins and other macromolecules tightly bind metals; in the latter, metals are bound relatively weakly to cellular ligands, including proteins and low molecular weight ligands. Fluorescent probes can be useful tools for studying the roles of transition metals in their labile forms. Probes for imaging transition metal dynamics in living systems must meet several stringent criteria. In addition to exhibiting desirable photophysical properties and biocompatibility, they must be selective and show a fluorescence turn-on response to the metal of interest. To meet this challenge, we have pursued two general strategies for metal detection, termed “recognition” and “reactivity”. Our design of transition metal probes makes use of a recognition-based approach for copper and nickel and a reactivity-based approach for cobalt and iron. This Account summarizes progress in our laboratory on both the development and application of fluorescent probes to identify and study the signaling roles of transition metals in biology. In conjunction with complementary methods for direct metal detection and genetic and/or pharmacological manipulations, fluorescent probes for transition metals have helped reveal a number of principles underlying transition metal dynamics. In this Account, we give

  4. Recognition- and reactivity-based fluorescent probes for studying transition metal signaling in living systems.

    PubMed

    Aron, Allegra T; Ramos-Torres, Karla M; Cotruvo, Joseph A; Chang, Christopher J

    2015-08-18

    Metals are essential for life, playing critical roles in all aspects of the central dogma of biology (e.g., the transcription and translation of nucleic acids and synthesis of proteins). Redox-inactive alkali, alkaline earth, and transition metals such as sodium, potassium, calcium, and zinc are widely recognized as dynamic signals, whereas redox-active transition metals such as copper and iron are traditionally thought of as sequestered by protein ligands, including as static enzyme cofactors, in part because of their potential to trigger oxidative stress and damage via Fenton chemistry. Metals in biology can be broadly categorized into two pools: static and labile. In the former, proteins and other macromolecules tightly bind metals; in the latter, metals are bound relatively weakly to cellular ligands, including proteins and low molecular weight ligands. Fluorescent probes can be useful tools for studying the roles of transition metals in their labile forms. Probes for imaging transition metal dynamics in living systems must meet several stringent criteria. In addition to exhibiting desirable photophysical properties and biocompatibility, they must be selective and show a fluorescence turn-on response to the metal of interest. To meet this challenge, we have pursued two general strategies for metal detection, termed "recognition" and "reactivity". Our design of transition metal probes makes use of a recognition-based approach for copper and nickel and a reactivity-based approach for cobalt and iron. This Account summarizes progress in our laboratory on both the development and application of fluorescent probes to identify and study the signaling roles of transition metals in biology. In conjunction with complementary methods for direct metal detection and genetic and/or pharmacological manipulations, fluorescent probes for transition metals have helped reveal a number of principles underlying transition metal dynamics. In this Account, we give three recent

  5. Ligational behavior of Schiff bases towards transition metal ion and metalation effect on their antibacterial activity.

    PubMed

    Devi, Jai; Batra, Nisha; Malhotra, Rajesh

    2012-11-01

    New Schiff bases pyrazine-2-carboxylicacid (phenyl-pyridin-2-yl-methylene)-hydrazide (Hpch-bp) HL(1) and pyrazine-2-carboxylicacid (pyridin-2-ylmethylene)-hydrazide (Hpch-pc) HL(2) derived from condensation of pyrazine carboxylic hydrazide (Hpch) with 2-benzoyl pyridine (bp) or pyridine 2-carbaldehyde (pc) and their transition metal complexes of type ML((1-2)2) have been synthesized, where M=Mn(II), Co(II), Ni(II), Cu(II) and Zn(II). Characterization of ligands and their metal complexes was carried out by elemental analysis, conductimetric studies, magnetic susceptibility, spectroscopic techniques (IR, UV-VIS, NMR, ESR, Mass) and thermogravimetric analysis. The physico-chemical studies revealed octahedral geometry or distorted octahedral geometry around metal ion. These azomethine Schiff base ligands acted as tridentate coordinating through carbonyl, azomethine and pyridine nitrogen present in the ligand. The thermodynamic and thermal properties of the complexes have been investigated and it was observed on the basis of these studies that thermal stability of complexes follows the order Mnmetal ions. The trend of growth inhibition in the complexes was found to be in the order: Cu>Mn>Ni>Co>Zn. PMID:22813991

  6. Strain Engineering for Transition Metal Dichalcogenides Based Field Effect Transistors.

    PubMed

    Shen, Tingting; Penumatcha, Ashish V; Appenzeller, Joerg

    2016-04-26

    Using electrical characteristics from three-terminal field-effect transistors (FETs), we demonstrate substantial strain induced band gap tunability in transition metal dichalcogenides (TMDs) in line with theoretical predictions and optical experiments. Devices were fabricated on flexible substrates, and a cantilever sample holder was used to apply uniaxial tensile strain to the various multilayer TMD FETs. Analyzing in particular transfer characteristics, we argue that the modified device characteristics under strain are clear evidence of a band gap reduction of 100 meV in WSe2 under 1.35% uniaxial tensile strain at room temperature. Furthermore, the obtained device characteristics imply that the band gap does not shrink uniformly under strain relative to a reference potential defined by the source/drain contacts. Instead, the band gap change is only related to a change of the conduction band edge of WSe2, resulting in a decrease in the Schottky barrier (SB) for electrons without any change for hole injection into the valence band. Simulations of SB device characteristics are employed to explain this point and to quantify our findings. Last, our experimental results are compared with DFT calculations under strain showing excellent agreement between theoretical predictions and the experimental data presented here. PMID:27043387

  7. Ultramicrosensors based on transition metal hexacyanoferrates for scanning electrochemical microscopy.

    PubMed

    Komkova, Maria A; Holzinger, Angelika; Hartmann, Andreas; Khokhlov, Alexei R; Kranz, Christine; Karyakin, Arkady A; Voronin, Oleg G

    2013-01-01

    We report here a way for improving the stability of ultramicroelectrodes (UME) based on hexacyanoferrate-modified metals for the detection of hydrogen peroxide. The most stable sensors were obtained by electrochemical deposition of six layers of hexacyanoferrates (HCF), more specifically, an alternating pattern of three layers of Prussian Blue and three layers of Ni-HCF. The microelectrodes modified with mixed layers were continuously monitored in 1 mM hydrogen peroxide and proved to be stable for more than 5 h under these conditions. The mixed layer microelectrodes exhibited a stability which is five times as high as the stability of conventional Prussian Blue-modified UMEs. The sensitivity of the mixed layer sensor was 0.32 A·M(-1)·cm(-2), and the detection limit was 10 µM. The mixed layer-based UMEs were used as sensors in scanning electrochemical microscopy (SECM) experiments for imaging of hydrogen peroxide evolution. PMID:24205459

  8. First-order metal-insulator transition not accompanied by the structural phase transition observed in VO2-based devices

    NASA Astrophysics Data System (ADS)

    Kim, Hyun-Tak; Chae, Byung-Gyu; Kim, Bong-Jun; Lee, Yong-Wook; Yun, Sun-Jin; Kang, Kwang-Yong

    2006-03-01

    An abrupt first-order metal-insulator transition (MIT) is observed during the application of a switching pulse voltage to VO2-based two-terminal devices. When the abrupt MIT occurs, the structural phase transition (SPT) is investigated by a micro- Raman spectroscopy and a micro-XRD. The result shows that the MIT is not accompanied with the structural phase transition (SPT); the abrupt MIT is prior to the SPT. Moreover, any switching pulse over a threshold voltage of 7.1 V for the MIT enabled the device material to transform efficiently from an insulator to a metal. The measured delay time from the source switching pulse to an induced MIT pulse is an order of 20 nsec which is much less than a delay time of about one msec deduced by thermal model. This indicates that the first-order MIT does not occur due to thermal. We think this MIT is the Mott transition. (Reference: New J. Phys. 6 (1994) 52 (www.njp.org), Appl. Phys. Lett. 86 (2005) 242101, Physica B 369 (2005. December) xxxx)

  9. Oligocyclopentadienyl transition metal complexes

    SciTech Connect

    de Azevedo, Cristina G.; Vollhardt, K. Peter C.

    2002-01-18

    Synthesis, characterization, and reactivity studies of oligocyclopentadienyl transition metal complexes, namely those of fulvalene, tercyclopentadienyl, quatercyclopentadienyl, and pentacyclopentadienyl(cyclopentadienyl) are the subject of this account. Thermal-, photo-, and redox chemistries of homo- and heteropolynuclear complexes are described.

  10. Graphene-based transition metal oxide nanocomposites for the oxygen reduction reaction

    NASA Astrophysics Data System (ADS)

    Sun, Meng; Liu, Huijuan; Liu, Yang; Qu, Jiuhui; Li, Jinghong

    2015-01-01

    The development of low cost, durable and efficient nanocatalysts to substitute expensive and rare noble metals (e.g. Pt, Au and Pd) in overcoming the sluggish kinetic process of the oxygen reduction reaction (ORR) is essential to satisfy the demand for sustainable energy conversion and storage in the future. Graphene based transition metal oxide nanocomposites have extensively been proven to be a type of promising highly efficient and economic nanocatalyst for optimizing the ORR to solve the world-wide energy crisis. Synthesized nanocomposites exhibit synergetic advantages and avoid the respective disadvantages. In this feature article, we concentrate on the recent leading works of different categories of introduced transition metal oxides on graphene: from the commonly-used classes (FeOx, MnOx, and CoOx) to some rare and heat-studied issues (TiOx, NiCoOx and Co-MnOx). Moreover, the morphologies of the supported oxides on graphene with various dimensional nanostructures, such as one dimensional nanocrystals, two dimensional nanosheets/nanoplates and some special multidimensional frameworks are further reviewed. The strategies used to synthesize and characterize these well-designed nanocomposites and their superior properties for the ORR compared to the traditional catalysts are carefully summarized. This work aims to highlight the meaning of the multiphase establishment of graphene-based transition metal oxide nanocomposites and its structural-dependent ORR performance and mechanisms.

  11. Graphene-based transition metal oxide nanocomposites for the oxygen reduction reaction.

    PubMed

    Sun, Meng; Liu, Huijuan; Liu, Yang; Qu, Jiuhui; Li, Jinghong

    2015-01-28

    The development of low cost, durable and efficient nanocatalysts to substitute expensive and rare noble metals (e.g. Pt, Au and Pd) in overcoming the sluggish kinetic process of the oxygen reduction reaction (ORR) is essential to satisfy the demand for sustainable energy conversion and storage in the future. Graphene based transition metal oxide nanocomposites have extensively been proven to be a type of promising highly efficient and economic nanocatalyst for optimizing the ORR to solve the world-wide energy crisis. Synthesized nanocomposites exhibit synergetic advantages and avoid the respective disadvantages. In this feature article, we concentrate on the recent leading works of different categories of introduced transition metal oxides on graphene: from the commonly-used classes (FeOx, MnOx, and CoOx) to some rare and heat-studied issues (TiOx, NiCoOx and Co-MnOx). Moreover, the morphologies of the supported oxides on graphene with various dimensional nanostructures, such as one dimensional nanocrystals, two dimensional nanosheets/nanoplates and some special multidimensional frameworks are further reviewed. The strategies used to synthesize and characterize these well-designed nanocomposites and their superior properties for the ORR compared to the traditional catalysts are carefully summarized. This work aims to highlight the meaning of the multiphase establishment of graphene-based transition metal oxide nanocomposites and its structural-dependent ORR performance and mechanisms. PMID:25502117

  12. 2D Transition-Metal-Dichalcogenide-Nanosheet-Based Composites for Photocatalytic and Electrocatalytic Hydrogen Evolution Reactions.

    PubMed

    Lu, Qipeng; Yu, Yifu; Ma, Qinglang; Chen, Bo; Zhang, Hua

    2016-03-01

    Hydrogen (H2) is one of the most important clean and renewable energy sources for future energy sustainability. Nowadays, photocatalytic and electrocatalytic hydrogen evolution reactions (HERs) from water splitting are considered as two of the most efficient methods to convert sustainable energy to the clean energy carrier, H2. Catalysts based on transition metal dichalcogenides (TMDs) are recognized as greatly promising substitutes for noble-metal-based catalysts for HER. The photocatalytic and electrocatalytic activities of TMD nanosheets for the HER can be further improved after hybridization with many kinds of nanomaterials, such as metals, oxides, sulfides, and carbon materials, through different methods including the in situ reduction method, the hot-injection method, the heating-up method, the hydro(solvo)thermal method, chemical vapor deposition (CVD), and thermal annealing. Here, recent progress in photocatalytic and electrocatalytic HERs using 2D TMD-based composites as catalysts is discussed. PMID:26676800

  13. Partial-surface-passivation strategy for transition-metal-based copper-gold nanocage.

    PubMed

    Liu, Shoujie; Zheng, Xusheng; Song, Li; Liu, Wei; Yao, Tao; Sun, Zhihu; Lin, Yue; Wei, Shiqiang

    2016-05-01

    An effective strategy involving the corrosion of partial-surface-passivated Cu nanoparticles is proposed for synthesizing transition-metal-based Cu-Au alloy nanocages. Time-dependent X-ray absorption spectroscopy demonstrates that the hollow-cage Cu-Au alloy nanostructure is formed by sequential erosion of the partial surface and interior Cu and by the alloying of Au and Cu. PMID:27116561

  14. Transition Metal Ion Complexes of Schiff-bases. Synthesis, Characterization and Antibacterial Properties

    PubMed Central

    Munawar, Asifa; Supuran, Claudiu T.

    2001-01-01

    Some novel transition metal [Co(II), Cu(II), Ni(II) and Zn(II)] complexes of substituted pyridine Schiff-bases have been prepared and characterized by physical, spectral and analytical data. The synthesized Schiff-bases act as deprotonated tridentate for the complexation reaction with Co(II), Ni(II) and Zn(II) ions. The new compounds, possessing the general formula [M(L)2] where [M=Co(II), Cu(II), Ni(II) and Zn(II) and HL=HL1, HL2, HL3 and HL4] show an octahedral geometry. In order to evaluate the effect of metal ions upon chelation, the Schiff bases and their complexes have been screened for antibacterial activity against the strains such as Escherichia coli,Staphylococcus aureus, and Pseudomonas aeruginosa. The complexed Schiff bases have shown to be more antibacterial against one more bacterial species as compared to uncomplexed Schiff-bases. PMID:18475987

  15. Synthesis and structures of transition metal pacman complexes of heteroditopic Schiff-base pyrrole macrocycles.

    PubMed

    Leeland, James W; Finn, Colin; Escuyer, Bérengère; Kawaguchi, Hiroyuki; Nichol, Gary S; Slawin, Alexandra M Z; Love, Jason B

    2012-12-01

    A series of polydentate dual-compartment, Schiff-base pyrrole macrocycles has been prepared through the straightforward Lewis acid catalysed [1 + 1] condensation reactions between ONO or O(5)-linked aryldiamines and dipyrromethane dialdehydes. These macrocycles display hydrogen-bond acceptor and donor properties and provide distinct N(4) and O(5)/ONO donor sets for metallation reactions, so forming alkali, alkaline earth, and transition metal complexes that were characterised spectroscopically and crystallographically. While the conformationally flexible O(5) donor set allows the formation of helical potassium salt structures, the transition metal complexes of all variants of these macrocycles invariably adopt wedged, Pacman-shaped structures in which the metal is bound in the pyrrole-imine N(4) donor set, so leaving the ONO/O(5) donor set pendant and apical. In some cases (V, Cr, and Co), this proximate combination of Lewis acid binding site and hydrogen bond acceptor facilitates the coordination of water within the molecular cleft; alternatively, direct interaction between the pendant arm and the metal is seen (e.g. Ti). Higher order [2 + 2] macrocycles were also prepared as minor, inseparable by-products of cyclisation, and Fe(2), Mn(2), and Co(2) complexes of these larger macrocycles were found to adopt binuclear helical structures by X-ray crystallography. PMID:23026851

  16. The strong reactions of Lewis-base noble-metals with vanadium and other acidic transition metals

    SciTech Connect

    Ebbinghaus, B.B.

    1991-05-01

    The noble metals often thought of as unreactive solids,react strongly with nearly 40% of the elements in the periodictable: group IIIB-VB transition metals, lanthanides, theactinides, and group IIIA-IVA non-transition metals. These strong reactions arise from increased bonding/electron transfer fromnonbonding electrons d electron pairs on the noble metal tovacant orbitals on V, etc. This effect is a generalized Lewis acid-base interaction. The partial Gibbs energy of V in the noblemetals has been measured as a function of concentration at a temperature near 1000C. Thermodynamics of the intermetallics are determined by ternary oxide equilibria, ternary carbide equilibria, and the high-temperature galvanic cell technique. These experimental methods use equilibrated solid composite mixtures in which grains of V oxides or of V carbides are interspersed with grains of V-NM(noble-metal) alloys. In equilibrium the activity of V in the oxide or the carbide equals the activity in the alloy. Consequently, the thermodynamics available in the literature for the V oxides and V carbides are reviewed. Test runs on the galvanic cell were attempted. The V oxide electrode reacts with CaF[sub 2], ThO[sub 2], YDT(0.85ThO[sub 2]-0.15YO[sub 1.5]), and LDT(0.85ThO[sub 2]- 0.15LaO[sub 1.5]) to interfere with the measured data observed toward the beginning of a galvanic cell experiment are the most accurate. The interaction of vanadium at infinite dilution in the noble-metals was determined.

  17. The strong reactions of Lewis-base noble-metals with vanadium and other acidic transition metals

    SciTech Connect

    Ebbinghaus, B.B.

    1991-05-01

    The noble metals often thought of as unreactive solids,react strongly with nearly 40% of the elements in the periodictable: group IIIB-VB transition metals, lanthanides, theactinides, and group IIIA-IVA non-transition metals. These strong reactions arise from increased bonding/electron transfer fromnonbonding electrons d electron pairs on the noble metal tovacant orbitals on V, etc. This effect is a generalized Lewis acid-base interaction. The partial Gibbs energy of V in the noblemetals has been measured as a function of concentration at a temperature near 1000C. Thermodynamics of the intermetallics are determined by ternary oxide equilibria, ternary carbide equilibria, and the high-temperature galvanic cell technique. These experimental methods use equilibrated solid composite mixtures in which grains of V oxides or of V carbides are interspersed with grains of V-NM(noble-metal) alloys. In equilibrium the activity of V in the oxide or the carbide equals the activity in the alloy. Consequently, the thermodynamics available in the literature for the V oxides and V carbides are reviewed. Test runs on the galvanic cell were attempted. The V oxide electrode reacts with CaF{sub 2}, ThO{sub 2}, YDT(0.85ThO{sub 2}-0.15YO{sub 1.5}), and LDT(0.85ThO{sub 2}- 0.15LaO{sub 1.5}) to interfere with the measured data observed toward the beginning of a galvanic cell experiment are the most accurate. The interaction of vanadium at infinite dilution in the noble-metals was determined.

  18. Superconductivity in transition metals.

    PubMed

    Slocombe, Daniel R; Kuznetsov, Vladimir L; Grochala, Wojciech; Williams, Robert J P; Edwards, Peter P

    2015-03-13

    A qualitative account of the occurrence and magnitude of superconductivity in the transition metals is presented, with a primary emphasis on elements of the first row. Correlations of the important parameters of the Bardeen-Cooper-Schrieffer theory of superconductivity are highlighted with respect to the number of d-shell electrons per atom of the transition elements. The relation between the systematics of superconductivity in the transition metals and the periodic table high-lights the importance of short-range or chemical bonding on the remarkable natural phenomenon of superconductivity in the chemical elements. A relationship between superconductivity and lattice instability appears naturally as a balance and competition between localized covalent bonding and so-called broken covalency, which favours d-electron delocalization and superconductivity. In this manner, the systematics of superconductivity and various other physical properties of the transition elements are related and unified. PMID:25666075

  19. Rapid Detection of Transition Metals in Welding Fumes Using Paper-Based Analytical Devices

    PubMed Central

    Volckens, John

    2014-01-01

    Metals in particulate matter (PM) are considered a driving factor for many pathologies. Despite the hazards associated with particulate metals, personal exposures for at-risk workers are rarely assessed due to the cost and effort associated with monitoring. As a result, routine exposure assessments are performed for only a small fraction of the exposed workforce. The objective of this research was to evaluate a relatively new technology, microfluidic paper-based analytical devices (µPADs), for measuring the metals content in welding fumes. Fumes from three common welding techniques (shielded metal arc, metal inert gas, and tungsten inert gas welding) were sampled in two welding shops. Concentrations of acid-extractable Fe, Cu, Ni, and Cr were measured and independently verified using inductively coupled plasma-optical emission spectroscopy (ICP-OES). Results from the µPAD sensors agreed well with ICP-OES analysis; the two methods gave statistically similar results in >80% of the samples analyzed. Analytical costs for the µPAD technique were ~50 times lower than market-rate costs with ICP-OES. Further, the µPAD method was capable of providing same-day results (as opposed several weeks for ICP laboratory analysis). Results of this work suggest that µPAD sensors are a viable, yet inexpensive alternative to traditional analytic methods for transition metals in welding fume PM. These sensors have potential to enable substantially higher levels of hazard surveillance for a given resource cost, especially in resource-limited environments. PMID:24515892

  20. Rapid detection of transition metals in welding fumes using paper-based analytical devices.

    PubMed

    Cate, David M; Nanthasurasak, Pavisara; Riwkulkajorn, Pornpak; L'Orange, Christian; Henry, Charles S; Volckens, John

    2014-05-01

    Metals in particulate matter (PM) are considered a driving factor for many pathologies. Despite the hazards associated with particulate metals, personal exposures for at-risk workers are rarely assessed due to the cost and effort associated with monitoring. As a result, routine exposure assessments are performed for only a small fraction of the exposed workforce. The objective of this research was to evaluate a relatively new technology, microfluidic paper-based analytical devices (µPADs), for measuring the metals content in welding fumes. Fumes from three common welding techniques (shielded metal arc, metal inert gas, and tungsten inert gas welding) were sampled in two welding shops. Concentrations of acid-extractable Fe, Cu, Ni, and Cr were measured and independently verified using inductively coupled plasma-optical emission spectroscopy (ICP-OES). Results from the µPAD sensors agreed well with ICP-OES analysis; the two methods gave statistically similar results in >80% of the samples analyzed. Analytical costs for the µPAD technique were ~50 times lower than market-rate costs with ICP-OES. Further, the µPAD method was capable of providing same-day results (as opposed several weeks for ICP laboratory analysis). Results of this work suggest that µPAD sensors are a viable, yet inexpensive alternative to traditional analytic methods for transition metals in welding fume PM. These sensors have potential to enable substantially higher levels of hazard surveillance for a given resource cost, especially in resource-limited environments. PMID:24515892

  1. Transition Metal Switchable Mirror

    SciTech Connect

    2009-01-01

    The switchable-mirrors technology was developed by Tom Richardson and Jonathan Slack of Berkeley Lab's Environmental Energy Technologies Division. By using transition metals rather than the rare earth metals used in the first metal-hydride switchable mirrors, Richardson and Slack were able to lower the cost and simplify the manufacturing process. Energy performance is improved as well, because the new windows can reflect or transmit both visible and infrared light. Besides windows for offices and homes, possible applications include automobile sunroofs, signs and displays, aircraft windows, and spacecraft. More information at: http://windows.lbl.gov/materials/chromogenics/default.htm

  2. Transition Metal Switchable Mirror

    ScienceCinema

    None

    2010-01-08

    The switchable-mirrors technology was developed by Tom Richardson and Jonathan Slack of Berkeley Lab's Environmental Energy Technologies Division. By using transition metals rather than the rare earth metals used in the first metal-hydride switchable mirrors, Richardson and Slack were able to lower the cost and simplify the manufacturing process. Energy performance is improved as well, because the new windows can reflect or transmit both visible and infrared light. Besides windows for offices and homes, possible applications include automobile sunroofs, signs and displays, aircraft windows, and spacecraft.

  3. Transition Metal Switchable Mirror

    ScienceCinema

    None

    2013-05-29

    The switchable-mirrors technology was developed by Tom Richardson and Jonathan Slack of Berkeley Lab's Environmental Energy Technologies Division. By using transition metals rather than the rare earth metals used in the first metal-hydride switchable mirrors, Richardson and Slack were able to lower the cost and simplify the manufacturing process. Energy performance is improved as well, because the new windows can reflect or transmit both visible and infrared light. Besides windows for offices and homes, possible applications include automobile sunroofs, signs and displays, aircraft windows, and spacecraft. More information at: http://windows.lbl.gov/materials/chromogenics/default.htm

  4. Transition Metal Switchable Mirror

    SciTech Connect

    2009-08-21

    The switchable-mirrors technology was developed by Tom Richardson and Jonathan Slack of Berkeley Lab's Environmental Energy Technologies Division. By using transition metals rather than the rare earth metals used in the first metal-hydride switchable mirrors, Richardson and Slack were able to lower the cost and simplify the manufacturing process. Energy performance is improved as well, because the new windows can reflect or transmit both visible and infrared light. Besides windows for offices and homes, possible applications include automobile sunroofs, signs and displays, aircraft windows, and spacecraft.

  5. Spectroscopic studies and biological activity of some transition metal complexes of unusual Schiff base

    NASA Astrophysics Data System (ADS)

    Abu Al-Nasr, Ahmad K.; Ramadan, Ramadan M.

    2013-03-01

    Unusual Schiff base ligand, 4-ethanimidoyl-6-[(1E)-N-(2-hydroxy-4-methylphenyl)ethanimidoyl]benzene-1,3-diol, L, was synthesized via catalytic process involving the interaction of some metal ions with a macrocyclic Schiff base (MSB). The transition metal derivatives [ML(H2O)4](NO3)3, M = Cr(III) and Fe(III), [NiL(H2O)4](NO3)2, [ML(H2O)2](NO3)2, M = Zn(II) and Cd(II), [Cl2Pd(μ-Cl)2PdL], [PtL(Cl)2] and [PtL(Cl)4] were also synthesized from the corresponding metal species with L. The Schiff bases and complexes were characterized by elemental analysis, mass spectrometry, IR and 1H NMR spectroscopy. The crystal structure of L was determined by X-ray analysis. The spectroscopic studies revealed a variety of structure arrangements for the complexes. The biological activities of L and metal complexes against the Escherchia coli as Gram-negative bacteria and Staphylococcus aureus as Gram-positive bacteria, and the two fungus Aspergillus flavus and Candida albicans were screened. The cytotoxicity of [PtL(Cl)2] complex, a cis-platin analogous, was checked as an antitumor agent on two breast cancer cell lines (MCF7 and T47D) and human liver carcinoma cell line (HepG2).

  6. Non-volatile memory based on transition metal perovskite oxide resistance switching

    NASA Astrophysics Data System (ADS)

    Nian, Yibo

    Driven by the non-volatile memory market looking for new advanced materials, this dissertation focuses on the study of non-volatile resistive random access memory (RRAM) based on transition metal perovskite oxides. Pr0.7Ca0.3MnO3 (PCMO), one of the representative materials in this family, has demonstrated a large range of resistance change when short electrical pulses with different polarity are applied. Such electrical-pulse-induced resistance (EPIR), with attractive features such as fast response, low power, high-density and non-volatility, makes PCMO and related materials promising candidates for non-volatile RRAM application. The objective of this work is to investigate, optimize and understand the properties of this universal EPIR behavior in transition metal perovskite oxide, represented by PCMO thin film devices. The research work includes fabrication of PCMO thin film devices, characterization of these EPIR devices as non-volatile memories, and investigation of their resistive switching mechanisms. The functionality of this perovskite oxide RRAM, including pulse magnitude/width dependence, power consumption, retention, endurance and radiation-hardness has been investigated. By studying the "shuttle tail" in hysteresis switching loops of oxygen deficient devices, a diffusion model with oxygen ions/vacancies as active agents at the metal/oxide interface is proposed for the non-volatile resistance switching effect in transition metal perovskite oxide thin films. The change of EPIR switching behavior after oxygen/argon ion implantation also shows experiment support for the proposed model. Furthermore, the universality, scalability and comparison with other non-volatile memories are discussed for future application.

  7. Transition-metal-nitride-based thin films as novel energy harvesting materials

    PubMed Central

    Kerdsongpanya, Sit; Alling, Björn

    2016-01-01

    The last few years have seen a rise in the interest in early transition-metal and rare-earth nitrides, primarily based on ScN and CrN, for energy harvesting by thermoelectricity and piezoelectricity. This is because of a number of important advances, among those the discoveries of exceptionally high piezoelectric coupling coefficient in (Sc,Al)N alloys and of high thermoelectric power factors of ScN-based and CrN-based thin films. These materials also constitute well-defined model systems for investigating thermodynamics of mixing for alloying and nanostructural design for optimization of phase stability and band structure. These features have implications for and can be used for tailoring of thermoelectric and piezoelectric properties. In this highlight article, we review the ScN- and CrN-based transition-metal nitrides for thermoelectrics, and drawing parallels with piezoelectricity. We further discuss these materials as a models systems for general strategies for tailoring of thermoelectric properties by integrated theoretical–experimental approaches. PMID:27358737

  8. Robust Quantum-Based Interatomic Potentials for Multiscale Modeling in Transition Metals

    SciTech Connect

    Moriarty, J A; Benedict, L X; Glosli, J N; Hood, R Q; Orlikowski, D A; Patel, M V; Soderlind, P; Streitz, F H; Tang, M; Yang, L H

    2005-03-25

    First-principles generalized pseudopotential theory (GPT) provides a fundamental basis for transferable multi-ion interatomic potentials in transition metals and alloys within density-functional quantum mechanics. In central bcc transition metals, where multi-ion angular forces are important to structural properties, simplified model GPT or MGPT potentials have been developed based on canonical d bands to allow analytic forms and large-scale atomistic simulations. Robust, advanced-generation MGPT potentials have now been obtained for Ta and Mo and successfully applied to a wide range of structural, thermodynamic, defect and mechanical properties at both ambient and extreme conditions. Selected applications to multiscale modeling discussed here include dislocation core structure and mobility, atomistically informed dislocation dynamics simulations of plasticity, and thermoelasticity and high-pressure strength modeling. Recent algorithm improvements have provided a more general matrix representation of MGPT beyond canonical bands, allowing improved accuracy and extension to f-electron actinide metals, an order of magnitude increase in computational speed for dynamic simulations, and the still-in-progress development of temperature-dependent potentials.

  9. Modularly designed transition metal PNP and PCP pincer complexes based on aminophosphines: synthesis and catalytic applications.

    PubMed

    Benito-Garagorri, David; Kirchner, Karl

    2008-02-01

    Transition metal complexes are indispensable tools for any synthetic chemist. Ideally, any metal-mediated process should be fast, clean, efficient, and selective and take place in a catalytic manner. These criteria are especially important considering that many of the transition metals employed in catalysis are rare and expensive. One of the ways of modifying and controlling the properties of transition metal complexes is the use of appropriate ligand systems, such as pincer ligands. Usually consisting of a central aromatic backbone tethered to two two-electron donor groups by different spacers, this class of tridentate ligands have found numerous applications in various areas of chemistry, including catalysis, due to their combination of stability, activity, and variability. As we focused on pincer ligands featuring phosphines as donor groups, the lack of a general method for the preparation of both neutral (PNP) and anionic (PCP) pincer ligands using similar precursor compounds as well as the difficulty of introducing chirality into the structure of pincer ligands prompted us to investigate the use of amines as spacers between the aromatic ring and the phosphines. By introduction of aminophosphine and phosphoramidite moieties into their structure, the synthesis of both PNP and PCP ligands can be achieved via condensation reactions between aromatic diamines and electrophilic chlorophosphines (or chlorophosphites). Moreover, chiral pincer complexes can be easily obtained by using building blocks obtained from the chiral pool. Thus, we have developed a modular synthetic strategy with which the steric, electronic, and stereochemical properties of the ligands can be varied systematically. With the ligands in hand, we studied their reactivity towards different transition metal precursors, such as molybdenum, ruthenium, iron, nickel, palladium, and platinum. This has resulted in the preparation of a range of new pincer complexes, including various iron complexes, as

  10. Transition metal sulfide loaded catalyst

    DOEpatents

    Maroni, Victor A.; Iton, Lennox E.; Pasterczyk, James W.; Winterer, Markus; Krause, Theodore R.

    1994-01-01

    A zeolite based catalyst for activation and conversion of methane. A zeolite support includes a transition metal (Mo, Cr or W) sulfide disposed within the micropores of the zeolite. The catalyst allows activation and conversion of methane to C.sub.2 + hydrocarbons in a reducing atmosphere, thereby avoiding formation of oxides of carbon.

  11. Performance limits of tunnel transistors based on mono-layer transition-metal dichalcogenides

    SciTech Connect

    Jiang, Xiang-Wei Li, Shu-Shen

    2014-05-12

    Performance limits of tunnel field-effect transistors based on mono-layer transition metal dichalcogenides are investigated through numerical quantum mechanical simulations. The atomic mono-layer nature of the devices results in a much smaller natural length λ, leading to much larger electric field inside the tunneling diodes. As a result, the inter-band tunneling currents are found to be very high as long as ultra-thin high-k gate dielectric is possible. The highest on-state driving current is found to be close to 600 μA/μm at V{sub g} = V{sub d} = 0.5 V when 2 nm thin HfO{sub 2} layer is used for gate dielectric, outperforming most of the conventional semiconductor tunnel transistors. In the five simulated transition-metal dichalcogenides, mono-layer WSe{sub 2} based tunnel field-effect transistor shows the best potential. Deep analysis reveals that there is plenty room to further enhance the device performance by either geometry, alloy, or strain engineering on these mono-layer materials.

  12. Novel Two-Dimensional Mechano-Electric Generators and Sensors Based on Transition Metal Dichalcogenides

    PubMed Central

    Yu, Sheng; Eshun, Kwesi; Zhu, Hao; Li, Qiliang

    2015-01-01

    Transition metal dichalcogenides (TMDCs), such as MoS2 and WSe2, provide two-dimensional atomic crystals with semiconductor band gap. In this work, we present a design of new mechano-electric generators and sensors based on transition metal dichalcogenide nanoribbon PN junctions and heterojunctions. The mechano-electric conversion was simulated by using a first-principle calculation. The output voltage of MoS2 nanoribbon PN junction increases with strain, reaching 0.036 V at 1% strain and 0.31 V at 8% strain, much larger than the reported results. Our study indicates that the length, width and layer number of TMDC nanoribbon PN junctions have an interesting but different impact on the voltage output. Also, the results indicate that doping position and concentration only cause a small fluctuation in the output voltage. These results have been compared with the mechano-electric conversion of TMDC heterojunctions. Such novel mechano-electric generators and sensors are very attractive for applications in future self-powered, wearable electronics and systems. PMID:26238461

  13. Novel Two-Dimensional Mechano-Electric Generators and Sensors Based on Transition Metal Dichalcogenides

    NASA Astrophysics Data System (ADS)

    Yu, Sheng; Eshun, Kwesi; Zhu, Hao; Li, Qiliang

    2015-08-01

    Transition metal dichalcogenides (TMDCs), such as MoS2 and WSe2, provide two-dimensional atomic crystals with semiconductor band gap. In this work, we present a design of new mechano-electric generators and sensors based on transition metal dichalcogenide nanoribbon PN junctions and heterojunctions. The mechano-electric conversion was simulated by using a first-principle calculation. The output voltage of MoS2 nanoribbon PN junction increases with strain, reaching 0.036 V at 1% strain and 0.31 V at 8% strain, much larger than the reported results. Our study indicates that the length, width and layer number of TMDC nanoribbon PN junctions have an interesting but different impact on the voltage output. Also, the results indicate that doping position and concentration only cause a small fluctuation in the output voltage. These results have been compared with the mechano-electric conversion of TMDC heterojunctions. Such novel mechano-electric generators and sensors are very attractive for applications in future self-powered, wearable electronics and systems.

  14. Novel Two-Dimensional Mechano-Electric Generators and Sensors Based on Transition Metal Dichalcogenides.

    PubMed

    Yu, Sheng; Eshun, Kwesi; Zhu, Hao; Li, Qiliang

    2015-01-01

    Transition metal dichalcogenides (TMDCs), such as MoS2 and WSe2, provide two-dimensional atomic crystals with semiconductor band gap. In this work, we present a design of new mechano-electric generators and sensors based on transition metal dichalcogenide nanoribbon PN junctions and heterojunctions. The mechano-electric conversion was simulated by using a first-principle calculation. The output voltage of MoS2 nanoribbon PN junction increases with strain, reaching 0.036 V at 1% strain and 0.31 V at 8% strain, much larger than the reported results. Our study indicates that the length, width and layer number of TMDC nanoribbon PN junctions have an interesting but different impact on the voltage output. Also, the results indicate that doping position and concentration only cause a small fluctuation in the output voltage. These results have been compared with the mechano-electric conversion of TMDC heterojunctions. Such novel mechano-electric generators and sensors are very attractive for applications in future self-powered, wearable electronics and systems. PMID:26238461

  15. Quasiparticle band structure of the almost-gapless transition-metal-based Heusler semiconductors

    NASA Astrophysics Data System (ADS)

    Tas, M.; Şaşıoǧlu, E.; Galanakis, I.; Friedrich, C.; Blügel, S.

    2016-05-01

    Transition-metal-based Heusler semiconductors are promising materials for a variety of applications ranging from spintronics to thermoelectricity. Employing the G W approximation within the framework of the FLAPW method, we study the quasiparticle band structure of a number of such compounds being almost gapless semiconductors. We find that in contrast to the s p -electron based semiconductors such as Si and GaAs, in these systems, the many-body corrections have a minimal effect on the electronic band structure and the energy band gap increases by less than 0.2 eV, which makes the starting point density functional theory (DFT) a good approximation for the description of electronic and optical properties of these materials. Furthermore, the band gap can be tuned either by the variation of the lattice parameter or by the substitution of the s p -chemical element.

  16. An ammonium soap solution based method for the preparation of ceramic/transition metal microcomposites

    SciTech Connect

    Robinson, D.A.; Maginnis, M.A.

    1995-12-01

    A process for the preparation of transition metal/ceramic composites has been developed. This method was initially used to prepare silver/Y BaCuO composites and is currently being used to prepare other transition metal/ceramic superconductors and metal nitrides. An ammonium soap of 2-ethylhexonate is used to prepare a metallorganic in solution that is rapidly gelled or precipitated around a suspended and dispersed ceramic. This step is followed by a low temperature heat treatment in hydrogen or oxygen to produce the desired composite.

  17. Selenophene transition metal complexes

    SciTech Connect

    White, C.J.

    1994-07-27

    This research shows that selenophene transition metal complexes have a chemistry that is similar to their thiophene analogs. Selenophene coordination has been demonstrated and confirmed by molecular structure in both the {eta}{sup 5}- and the {eta}{sup 1}(Se)-coordination modes. The reaction chemistry of selenophene complexes closely resembles that of the analogous thiophene complexes. One major difference, however, is that selenophene is a better donor ligand than thiophene making the selenophene complexes more stable than the corresponding thiophene complexes. The {sup 77}Se NMR chemical shift values for selenophene complexes fall within distinct regions primarily depending on the coordination mode of the selenophene ligand. In the final paper, the C-H bond activation of {eta}{sup 1}(S)-bound thiophenes, {eta}{sup 1}(S)-benzothiophene and {eta}{sup 1}(Se)-bound selenophenes has been demonstrated. The deprotonation and rearrangement of the {eta}{sup 1}(E)-bound ligand to the carbon bound L-yl complex readily occurs in the presence of base. Reprotonation with a strong acid gives a carbene complex that is unreactive towards nucleophilic attack at the carbene carbon and is stable towards exposure to air. The molecular structure of [Cp(NO)(PPh{sub 3})Re(2-benzothioenylcarbene)]O{sub 3}SCF{sub 3} was determined and contains a Re-C bond with substantial double bond character. Methyl substitution for the thienylcarbene or selenylcarbene gives a carbene that rearranges thermally to give back the {eta}{sup 1}(E)-bound complex. Based on these model reactions, a new mechanism for the H/D exchange of thiophene over the hydrodesulfurization catalyst has been proposed.

  18. Robust Quantum-Based Interatomic Potentials for Multiscale Modeling in Transition Metals

    SciTech Connect

    Moriarty, J A; Benedict, L X; Glosli, J N; Hood, R Q; Orlikowski, D A; Patel, M V; Soderlind, P; Streitz, F H; Tang, M; Yang, L H

    2005-09-27

    First-principles generalized pseudopotential theory (GPT) provides a fundamental basis for transferable multi-ion interatomic potentials in transition metals and alloys within density-functional quantum mechanics. In the central bcc metals, where multi-ion angular forces are important to materials properties, simplified model GPT or MGPT potentials have been developed based on canonical d bands to allow analytic forms and large-scale atomistic simulations. Robust, advanced-generation MGPT potentials have now been obtained for Ta and Mo and successfully applied to a wide range of structural, thermodynamic, defect and mechanical properties at both ambient and extreme conditions. Selected applications to multiscale modeling discussed here include dislocation core structure and mobility, atomistically informed dislocation dynamics simulations of plasticity, and thermoelasticity and high-pressure strength modeling. Recent algorithm improvements have provided a more general matrix representation of MGPT beyond canonical bands, allowing improved accuracy and extension to f-electron actinide metals, an order of magnitude increase in computational speed for dynamic simulations, and the development of temperature-dependent potentials.

  19. Spin treatment-based approach for electronic transport in paramagnetic liquid transition metals

    NASA Astrophysics Data System (ADS)

    Grosdidier, B.; Ben Abdellah, A.; Bouziane, K.; Mujibur Rahman, S. M.; Gasser, J. G.

    2013-09-01

    A novel concept is proposed to calculate both the electrical resistivity and thermoelectric power (TEP) of liquid transition metals (Mn, Fe, Co and Ni) characterized by a paramagnetic state in the liquid phase. By contrast to a previous work (PRB64, 094202 (2001)), where the resistivity was calculated by treating separately the interactions between spin up and spin down using the Matthiessen rule, our current approach is based on two types of muffin tin potentials in the t-matrix, namely spin up and spin down. The resistivity is treated as the result of the interference of the two kinds of spin states of electrons including a cross-contribution. The calculated resistivity values agree reasonably well with the available experimental ones for all the metals considered. Moreover, the calculated TEP, as deduced from the slope of resistivity vs. energy, has been found to be positive for Mn and Fe but negative for Co and Ni. Besides that, this formalism for resistivity calculation may be generalized to a system that may exist in different atomic states. It is worth mentioning that this concept is analogous to the one used in the process of neutron scattering on a metal composed of multiple isotopes.

  20. Thermodynamics of several lewis-acid-base stabilized transition metal alloys

    NASA Astrophysics Data System (ADS)

    Gibson, John K.; Brewer, Leo; Gingerich, Karl A.

    1984-11-01

    High-temperature (1425 to 2750 K) thermodynamic activities of one or both components of twenty-five binary alloys of a group IVB-VIB element (Ti, Zr, Hf, Nb, Ta, or W) with a platinum group element (Ru, Os, Ir, Pd, Pt, or Au) have been determined by equilibrating the alloy with the appropriate carbide and graphite, equilibrating with the nitride and nitrogen gas, or measuring the partial vapor pressure(s) thermogravimetrically or mass spectrometrically. The extraordinary stability of this class of transition metal alloy is attributed to a generalized Lewis-acid-base interaction involving valence d electrons, and the results of these investigations are interpreted within the context of this effect. Among the conclusions made are that a non-spherically-symmetrical crystal field significantly reduces the bonding effectiveness of certain valence d orbitals; the effect of the extent of derealization of these orbitals is also considered.

  1. A high-performance complementary inverter based on transition metal dichalcogenide field-effect transistors.

    PubMed

    Cho, Ah-Jin; Park, Kee Chan; Kwon, Jang-Yeon

    2015-01-01

    For several years, graphene has been the focus of much attention due to its peculiar characteristics, and it is now considered to be a representative 2-dimensional (2D) material. Even though many research groups have studied on the graphene, its intrinsic nature of a zero band-gap, limits its use in practical applications, particularly in logic circuits. Recently, transition metal dichalcogenides (TMDs), which are another type of 2D material, have drawn attention due to the advantage of having a sizable band-gap and a high mobility. Here, we report on the design of a complementary inverter, one of the most basic logic elements, which is based on a MoS2 n-type transistor and a WSe2 p-type transistor. The advantages provided by the complementary metal-oxide-semiconductor (CMOS) configuration and the high-performance TMD channels allow us to fabricate a TMD complementary inverter that has a high-gain of 13.7. This work demonstrates the operation of the MoS2 n-FET and WSe2 p-FET on the same substrate, and the electrical performance of the CMOS inverter, which is based on a different driving current, is also measured. PMID:25852410

  2. A high-performance complementary inverter based on transition metal dichalcogenide field-effect transistors

    NASA Astrophysics Data System (ADS)

    Cho, Ah-Jin; Park, Kee Chan; Kwon, Jang-Yeon

    2015-03-01

    For several years, graphene has been the focus of much attention due to its peculiar characteristics, and it is now considered to be a representative 2-dimensional (2D) material. Even though many research groups have studied on the graphene, its intrinsic nature of a zero band-gap, limits its use in practical applications, particularly in logic circuits. Recently, transition metal dichalcogenides (TMDs), which are another type of 2D material, have drawn attention due to the advantage of having a sizable band-gap and a high mobility. Here, we report on the design of a complementary inverter, one of the most basic logic elements, which is based on a MoS2 n-type transistor and a WSe2 p-type transistor. The advantages provided by the complementary metal-oxide-semiconductor (CMOS) configuration and the high-performance TMD channels allow us to fabricate a TMD complementary inverter that has a high-gain of 13.7. This work demonstrates the operation of the MoS2 n-FET and WSe2 p-FET on the same substrate, and the electrical performance of the CMOS inverter, which is based on a different driving current, is also measured.

  3. Characterization of Pt-based Transition Metal Alloy Electrodes for PEFC

    SciTech Connect

    Uebayashi, M.; Sato, Y.; Jeyadevan, B.; Tohji, K.; Sawada, Y.; Itoh, T.

    2007-03-20

    Pt metal is generally used as electrocatalyst in polymer electrolyte fuel cells (PEFC). However, the catalytic action of Pt anode is obstructed by the adsorption of CO gas molecules on to their surface and consequently the efficiency of the fuel cell decreases. Moreover, the activity of PEFC deteriorates even if the presence of CO is as low as 100 ppm. In this paper, attempts are being made to replace the Pt with Pt-based transition metal alloys such as PtFe and PtCo to overcome the above problem and also to improve the activity of fuel cells. The PtFe/C and PtCo/C necessary for the preparation of the electrodes were synthesized by depositing PtFe and PtCo particles synthesized using the polyol process on to the surface ketjenblack. From the results of cyclic voltammetry, we could confirm that PtFe/C could be used as an alternate material of Pt/C. However, Fe ions get eluted in the electrolyte. Thus, the study that can control the elution of Fe ion is necessary. Also in case of PtCo/C, we could confirm that Co ion doesn't get to elute, however the hydrogen oxidation reaction current is quite low.

  4. Dinuclear first-row transition metal complexes with a naphthyridine-based dinucleating ligand.

    PubMed

    Davenport, T C; Tilley, T D

    2015-07-21

    A series of dinuclear and tetranuclear first-row transition metal complexes were synthesized with the dinucleating ligand 2,7-bis(di(2-pyridyl)fluoromethyl)-1,8-naphthyridine (DPFN). The coordination pocket and rigidity of the DPFN ligand enforces pseudo-octahedral geometries about the metal centers that contain chloro, hydroxo, and aqua bridging ligands forming a "diamond" shaped configuration with metal-metal distances varying from 2.7826(5) to 3.2410(11) Å. Each metal center in the dinuclear complexes has an additional open coordination site that accommodates terminal ligands in a syn geometry of particular interest in catalyst design. The complexes are characterized by electronic spectroscopy, electrochemistry and potentiometric titration methods. PMID:25420206

  5. Carrier behavior in special multilayer device composed of different transition metal oxide-based intermediate connectors

    NASA Astrophysics Data System (ADS)

    Deng, Yan-Hong; Chen, Xiang-Yu; Ou, Qing-Dong; Wang, Qian-Kun; Jiang, Xiao-Cheng; Zhang, Dan-Dan; Li, Yan-Qing

    2014-06-01

    The impact of illumination on the connection part of the tandem organic light-emitting diodes was studied by using a special organic multilayer sample consisted of two organic active layers coupled with different transition metal oxide (TMO)-based intermediate connectors (ICs). Through measuring the current density-voltage characteristic, interfacial electronic structures, and capacitance-voltage characteristic, we observe an unsymmetrical phenomenon in current density-voltage and capacitance-voltage curves of Mg:Alq3/MoO3 and MoO3 composed devices, which was induced by the charge spouting zone near the ICs region and the recombination state in the MoO3 layer. Moreover, Mg:Alq3/MoO3 composed device displays a photovoltaic effect and the Voc shifts to forward bias under illumination. Our results demonstrate that the TMO-based IC structure coupled with photovoltaic effect can be a good approach for the study of photodetector, light sensor, and so on.

  6. Discovery of a 3d-transition-metal-based ferromagnetic Kondo lattice system

    NASA Astrophysics Data System (ADS)

    Us Saleheen, Ahmad; Samanta, Tapas; Lepkowski, Daniel; Shankar, Alok; Prestigiacomo, Joseph; Dubenko, Igor; Quetz, Abdiel; McDougald, Roy, Jr.; McCandless, Gregory; Chan, Julia; Adams, Philip; Young, David; Ali, Naushad; Stadler, Shane

    2015-03-01

    The formation of a Kondo lattice results in a wide variety of exotic phenomena associated with the competition between the Kondo effect and the RKKY interaction, such as heavy fermions, non-Fermi liquid behavior, unconventional superconductivity, and so on. A quantum critical point (QCP) has been frequently observed at the boundaries of competing phases for antiferromagnetic materials. However, the existence of a ferromagnetic (FM) QCP is unclear. Moreover, FM Kondo lattices are rare. Here we report the discovery of a FM Kondo lattice system Mn1-xFexCoGe, which is the first example of a 3d-metal-based system (i.e., not rare-earth-based). Resistivity, magnetic susceptibility, heat capacity and thermopower studies on a single crystal sample indicate that the anisotropic FM kondo lattice has formed along c-axis. The signature of a spin density wave transition was also observed above the Kondo minimum, below which the resistivity follows a log(T) behavior. This work was supported by the U.S. Department of Energy (Grant Nos. DE-FG02-13ER46946 and DE-FG02-06ER46291).

  7. Quantum simulation of a heterojunction vertical tunnel FET based on 2D transition metal dichalcogenides

    NASA Astrophysics Data System (ADS)

    Cao, Jiang; Cresti, Alessandro; Esseni, David; Pala, Marco

    2016-02-01

    We simulate a band-to-band tunneling field-effect transistor based on a vertical heterojunction of single-layer MoS2 and WTe2, by exploiting the non-equilibrium Green's function method and including electron-phonon scattering. For both in-plane and out-of-plane transport, we attempt to calibrate out models to the few available experimental results. We focus on the role of chemical doping and back-gate biasing, and investigate the off-state physics of this device by analyzing the influence of the top-gate geometrical alignment on the device performance. The device scalability as a function of gate length is also studied. Finally, we present two metrics for the switching delay and energy of the device. Our simulations indicate that vertical field-effect transistors based on transition metal dichalcogenides can provide very small values of sub-threshold swing when properly designed in terms of doping concentration and top-gate extension length.

  8. Carrier behavior in special multilayer device composed of different transition metal oxide-based intermediate connectors

    SciTech Connect

    Deng, Yan-Hong; Chen, Xiang-Yu E-mail: xychen@suda.edu.cn; Ou, Qing-Dong; Wang, Qian-Kun; Jiang, Xiao-Cheng; Zhang, Dan-Dan; Li, Yan-Qing E-mail: xychen@suda.edu.cn

    2014-06-02

    The impact of illumination on the connection part of the tandem organic light-emitting diodes was studied by using a special organic multilayer sample consisted of two organic active layers coupled with different transition metal oxide (TMO)-based intermediate connectors (ICs). Through measuring the current density-voltage characteristic, interfacial electronic structures, and capacitance-voltage characteristic, we observe an unsymmetrical phenomenon in current density-voltage and capacitance-voltage curves of Mg:Alq{sub 3}/MoO{sub 3} and MoO{sub 3} composed devices, which was induced by the charge spouting zone near the ICs region and the recombination state in the MoO{sub 3} layer. Moreover, Mg:Alq{sub 3}/MoO{sub 3} composed device displays a photovoltaic effect and the V{sub oc} shifts to forward bias under illumination. Our results demonstrate that the TMO-based IC structure coupled with photovoltaic effect can be a good approach for the study of photodetector, light sensor, and so on.

  9. Trends in Ground-State Entropies for Transition Metal Based Hydrogen Atom Transfer Reactions

    SciTech Connect

    Mader, Elizabeth A.; Manner, Virginia W.; Markle, Todd F.; Wu, Adam; Franz, James A.; Mayer, James M.

    2009-03-10

    Reported herein are thermochemical studies of hydrogen atom transfer (HAT) reactions involving transition metal H-atom donors MIILH and oxyl radicals. [FeII(H2bip)3]2+, [FeII(H2bim)3]2+, [CoII(H2bim)3]2+ and RuII(acac)2(py-imH) [H2bip = 2,2’-bi-1,4,5,6-tetrahydro¬pyrimidine, H2bim = 2,2’-bi-imidazoline, acac = 2,4-pentandionato, py-imH = 2-(2’-pyridyl)¬imidazole)] each react with TEMPO (2,2,6,6-tetramethyl-1-piperidinoxyl) or tBu3PhO• (2,4,6-tri-tert-butylphenoxyl) to give the deprotonated, oxidized metal complex MIIIL, and TEMPOH or tBu3PhOH. Solution equilibrium measurements for the reactions of Co and Fe complexes with TEMPO show a large, negative ground-state entropy for hydrogen atom transfer: ΔSºHAT = -30 ± 2 cal mol-1 K-1 for the two iron complexes and -41 ± 2 cal mol-1 K-1 for [CoII(H2bim)3]2+. The ΔSºHAT for TEMPO + RuII(acac)2(py-imH) is much closer to zero, 4.9 ± 1.1 cal mol-1 K-1. Calorimetric measurements quantitatively confirm the enthalpy of reaction for [FeII(H2bip)3]2+ + TEMPO, thus also confirming ΔSºHAT. Calorimetry on TEMPOH + tBu3PhO• gives ΔHºHAT = 11.2 ± 0.5 kcal mol-1 which matches the enthalpy predicted from the difference in literature solution BDEs. An evaluation of the literature BDEs of both TEMPOH and tBu3PhOH is briefly presented and new estimates are included on the relative enthalpy of solvation for tBu3PhO• vs. tBu3PhOH. The primary contributor to the large magnitude of the ground-state entropy |ΔSºHAT| for the metal complexes is vibrational entropy, ΔSºvib. The common assumption that ΔSºHAT ≈ 0 for HAT reactions, developed for organic and small gas phase molecules, does not hold for transition metal based HAT reactions. The trend in magnitude of |ΔSºHAT| for reactions with TEMPO, RuII(acac)2(py-imH) << [FeII(H2bip)3]2+ = [FeII(H2bim)3]2+ < [CoII(H2bim)3]2+, is surprisingly well predicted by the trends for electron transfer half-reaction entropies, ΔSºET, in aprotic solvents. ΔSºET and

  10. Sensitivity Enhancement of Transition Metal Dichalcogenides/Silicon Nanostructure-based Surface Plasmon Resonance Biosensor

    NASA Astrophysics Data System (ADS)

    Ouyang, Qingling; Zeng, Shuwen; Jiang, Li; Hong, Liying; Xu, Gaixia; Dinh, Xuan-Quyen; Qian, Jun; He, Sailing; Qu, Junle; Coquet, Philippe; Yong, Ken-Tye

    2016-06-01

    In this work, we designed a sensitivity-enhanced surface plasmon resonance biosensor structure based on silicon nanosheet and two-dimensional transition metal dichalcogenides. This configuration contains six components: SF10 triangular prism, gold thin film, silicon nanosheet, two-dimensional MoS2/MoSe2/WS2/WSe2 (defined as MX2) layers, biomolecular analyte layer and sensing medium. The minimum reflectivity, sensitivity as well as the Full Width at Half Maximum of SPR curve are systematically examined by using Fresnel equations and the transfer matrix method in the visible and near infrared wavelength range (600 nm to 1024 nm). The variation of the minimum reflectivity and the change in resonance angle as the function of the number of MX2 layers are presented respectively. The results show that silicon nanosheet and MX2 layers can be served as effective light absorption medium. Under resonance conditions, the electrons in these additional dielectric layers can be transferred to the surface of gold thin film. All silicon-MX2 enhanced sensing models show much better performance than that of the conventional sensing scheme where pure Au thin film is used, the highest sensitivity can be achieved by employing 600 nm excitation light wavelength with 35 nm gold thin film and 7 nm thickness silicon nanosheet coated with monolayer WS2.

  11. Sensitivity Enhancement of Transition Metal Dichalcogenides/Silicon Nanostructure-based Surface Plasmon Resonance Biosensor

    PubMed Central

    Ouyang, Qingling; Zeng, Shuwen; Jiang, Li; Hong, Liying; Xu, Gaixia; Dinh, Xuan-Quyen; Qian, Jun; He, Sailing; Qu, Junle; Coquet, Philippe; Yong, Ken-Tye

    2016-01-01

    In this work, we designed a sensitivity-enhanced surface plasmon resonance biosensor structure based on silicon nanosheet and two-dimensional transition metal dichalcogenides. This configuration contains six components: SF10 triangular prism, gold thin film, silicon nanosheet, two-dimensional MoS2/MoSe2/WS2/WSe2 (defined as MX2) layers, biomolecular analyte layer and sensing medium. The minimum reflectivity, sensitivity as well as the Full Width at Half Maximum of SPR curve are systematically examined by using Fresnel equations and the transfer matrix method in the visible and near infrared wavelength range (600 nm to 1024 nm). The variation of the minimum reflectivity and the change in resonance angle as the function of the number of MX2 layers are presented respectively. The results show that silicon nanosheet and MX2 layers can be served as effective light absorption medium. Under resonance conditions, the electrons in these additional dielectric layers can be transferred to the surface of gold thin film. All silicon-MX2 enhanced sensing models show much better performance than that of the conventional sensing scheme where pure Au thin film is used, the highest sensitivity can be achieved by employing 600 nm excitation light wavelength with 35 nm gold thin film and 7 nm thickness silicon nanosheet coated with monolayer WS2. PMID:27305974

  12. Passively Q-switched waveguide lasers based on two-dimensional transition metal diselenide.

    PubMed

    Cheng, Chen; Liu, Hongliang; Tan, Yang; Vázquez de Aldana, Javier R; Chen, Feng

    2016-05-16

    We reported on the passively Q-switched waveguide lasers based on few-layer transition metal diselenide, including molybdenum diselenide (MoSe2) and tungsten diselenide (WSe2), as saturable absorbers. The MoSe2 and WSe2 membranes were covered on silica wafers by chemical vapor deposition (CVD). A low-loss depressed cladding waveguide was produced by femtosecond laser writing in a Nd:YAG crystal. Under optical pump at 808 nm, the passive Q-switching of the Nd:YAG waveguide lasing at 1064 nm was achieved, reaching maximum average output power of 115 mW (MoSe2) and 45 mW (WSe2), respectively, which are corresponding to single-pulse energy of 36 nJ and 19 nJ. The repetition rate of the Q-switched waveguide lasers was tunable from 0.995 to 3.334 MHz (MoSe2) and 0.781 to 2.938 MHz (WSe2), and the obtained minimum pulse duration was 80ns (MoSe2) and 52 ns (WSe2), respectively. PMID:27409862

  13. Sensitivity Enhancement of Transition Metal Dichalcogenides/Silicon Nanostructure-based Surface Plasmon Resonance Biosensor.

    PubMed

    Ouyang, Qingling; Zeng, Shuwen; Jiang, Li; Hong, Liying; Xu, Gaixia; Dinh, Xuan-Quyen; Qian, Jun; He, Sailing; Qu, Junle; Coquet, Philippe; Yong, Ken-Tye

    2016-01-01

    In this work, we designed a sensitivity-enhanced surface plasmon resonance biosensor structure based on silicon nanosheet and two-dimensional transition metal dichalcogenides. This configuration contains six components: SF10 triangular prism, gold thin film, silicon nanosheet, two-dimensional MoS2/MoSe2/WS2/WSe2 (defined as MX2) layers, biomolecular analyte layer and sensing medium. The minimum reflectivity, sensitivity as well as the Full Width at Half Maximum of SPR curve are systematically examined by using Fresnel equations and the transfer matrix method in the visible and near infrared wavelength range (600 nm to 1024 nm). The variation of the minimum reflectivity and the change in resonance angle as the function of the number of MX2 layers are presented respectively. The results show that silicon nanosheet and MX2 layers can be served as effective light absorption medium. Under resonance conditions, the electrons in these additional dielectric layers can be transferred to the surface of gold thin film. All silicon-MX2 enhanced sensing models show much better performance than that of the conventional sensing scheme where pure Au thin film is used, the highest sensitivity can be achieved by employing 600 nm excitation light wavelength with 35 nm gold thin film and 7 nm thickness silicon nanosheet coated with monolayer WS2. PMID:27305974

  14. Trends in Ground-State Entropies for Transition Metal Based Hydrogen Atom Transfer Reactions

    PubMed Central

    Mader, Elizabeth A.; Manner, Virginia W.; Markle, Todd F.; Wu, Adam; Franz, James A.; Mayer, James M.

    2009-01-01

    Reported herein are thermochemical studies of hydrogen atom transfer (HAT) reactions involving transition metal H-atom donors MIILH and oxyl radicals. [FeII(H2bip)3]2+, [FeII(H2bim)3]2+, [CoII(H2bim)3]2+ and RuII(acac)2(py-imH) [H2bip = 2,2’-bi-1,4,5,6-tetrahydropyrimidine, H2bim = 2,2’-bi-imidazoline, acac = 2,4-pentandionato, py-imH = 2-(2’-pyridyl)-imidazole)] each react with TEMPO (2,2,6,6-tetramethyl-1-piperidinoxyl) or tBu3PhO• (2,4,6-tri-tert-butylphenoxyl) to give the deprotonated, oxidized metal complex MIIIL, and TEMPOH or tBu3PhOH. Solution equilibrium measurements for the reaction of [CoII(H2bim)3]2+ with TEMPO show a large, negative ground-state entropy for hydrogen atom transfer, −41 ± 2 cal mol−1 K−1. This is even more negative than the ΔSoHAT = −30 ± 2 cal mol−1 K−1 for the two iron complexes and the ΔSoHAT for RuII(acac)2(py-imH) + TEMPO, 4.9 ± 1.1 cal mol−1 K−1, as reported earlier. Calorimetric measurements quantitatively confirm the enthalpy of reaction for [FeII(H2bip)3]2+ + TEMPO, thus also confirming ΔSoHAT. Calorimetry on TEMPOH + tBu3PhO• gives ΔHoHAT = −11.2 ± 0.5 kcal mol−1 which matches the enthalpy predicted from the difference in literature solution BDEs. A brief evaluation of the literature thermochemistry of TEMPOH and tBu3PhOH supports the common assumption that ΔSoHAT ≈ 0 for HAT reactions of organic and small gas-phase molecules. However, this assumption does not hold for transition metal based HAT reactions. The trend in magnitude of |ΔSoHAT| for reactions with TEMPO, RuII(acac)2(py-imH) << [FeII(H2bip)3]2+ = [FeII(H2bim)3]2+ < [CoII(H2bim)3]2+, is surprisingly well predicted by the trends for electron transfer half-reaction entropies, ΔSoET, in aprotic solvents. This is because both ΔSoET and ΔSoHAT have substantial contributions from vibrational entropy, which varies significantly with the metal center involved. The close connection between ΔSoHAT and ΔSoET provides an important

  15. Transition metals activate TFEB in overexpressing cells

    PubMed Central

    Peña, Karina A.; Kiselyov, Kirill

    2015-01-01

    Transition metal toxicity is an important factor in the pathogenesis of numerous human disorders, including neurodegenerative diseases. Lysosomes have emerged as important factors in transition metal toxicity because they handle transition metals via endocytosis, autophagy, absorption from the cytoplasm and exocytosis. Transcription factor EB (TFEB) regulates lysosomal biogenesis and the expression of lysosomal proteins in response to lysosomal and/or metabolic stresses. Since transition metals cause lysosomal dysfunction, we proposed that TFEB may be activated to drive gene expression in response to transition metal exposure and that such activation may influence transition metal toxicity. We found that transition metals copper (Cu) and iron (Fe) activate recombinant TFEB and stimulate the expression of TFEB-dependent genes in TFEB-overexpressing cells. In cells that show robust lysosomal exocytosis, TFEB was cytoprotective at moderate levels of Cu exposure, decreasing oxidative stress as reported by the expression of heme oxygenase-1 (HMOX1) gene. However, at high levels of Cu exposure, particularly in cells with low levels of lysosomal exocytosis, activation of overexpressed TFEB was toxic, increasing oxidative stress and mitochondrial damage. Based on these data, we conclude that TFEB-driven gene network is a component of the cellular response to transition metals. These data suggest limitations and disadvantages of TFEB overexpression as a therapeutic approach. PMID:26251447

  16. Base-catalyzed synthesis of substituted indazoles under mild, transition-metal-free conditions.

    PubMed

    Thomé, Isabelle; Besson, Claire; Kleine, Tillmann; Bolm, Carsten

    2013-07-15

    Back to basics: A transition-metal-free method developed for the synthesis of indazoles involves an inexpensive catalytic system composed of a diamine and K2CO3. Various (Z)-2-bromoacetophenone tosylhydrazones were converted into indazoles at room temperature in excellent yields (see example; Ts = p-toluenesulfonyl). The yield was improved by photoisomerization with UV light when E/Z isomeric mixtures of the starting material were used. PMID:23740864

  17. M(5)-silicon (M= titanium, niobium, molybdenum) based transition-metal silicides for high temperature applications

    NASA Astrophysics Data System (ADS)

    Tang, Zhihong

    2007-12-01

    Transition metal silicides are being considered for future engine turbine components at temperatures up to 1600ºC. Although significant improvement in high temperature strength, room temperature fracture toughness has been realized in the past decade, further improvement in oxidation resistance is needed. Oxidation mechanism of Ti5Si3-based alloys was investigated. Oxidation behavior of Ti5Si3-based alloy strongly depends on the atmosphere. Presence of Nitrogen alters the oxidation behavior of Ti5Si3 by nucleation and growth of nitride subscale. Ti5Si3.2 and Ti5Si3C0.5 alloys exhibited an excellent oxidation resistance in nitrogen bearing atmosphere due to limited dissolution of nitrogen and increased Si/Ti activity ratio. MoSi2 coating developed by pack cementation to protect Mo-based Mo-Si-B composites was found to be effective up to 1500ºC. Shifting coating composition to T1+T2+Mo3Si region showed the possibility to extend the coating lifetime above 1500ºC by more than ten times via formation of slow growing Mo3Si or T2 interlayer without sacrificing the oxidation resistance of the coating. The phase equilibria in the Nb-rich portion of Nb-B system has been evaluated experimentally using metallographic analysis and differential thermal analyzer (DTA). It was shown that Nbss (solid solution) and NbB are the only two primary phases in the 0-40 at.% B composition range, and the eutectic reaction L ↔ Nbss + NbB was determined to occur at 2104+/-5°C by DTA.

  18. Electrical Conductivity in Transition Metals

    ERIC Educational Resources Information Center

    Talbot, Christopher; Vickneson, Kishanda

    2013-01-01

    The aim of this "Science Note" is to describe how to test the electron-sea model to determine whether it accurately predicts relative electrical conductivity for first-row transition metals. In the electron-sea model, a metal crystal is viewed as a three-dimensional array of metal cations immersed in a sea of delocalised valence…

  19. Molecular Structures, Acid-Base Properties, and Formation of Group 6 Transition Metal Hydroxides

    SciTech Connect

    Li, Shenggang; Guenther, Courtney L.; Kelley, Matthew S.; Dixon, David A.

    2011-04-28

    Density functional theory (DFT) and coupled cluster theory (CCSD(T)) were used to study the group 6 metal (M = Cr, Mo, W) hydroxides: MO3-m(OH)2m (m = 1-3), M2O6-m(OH)2m (m = 1-5), M3O9-m(OH)2m (m = 1, 2), and M4O11(OH)2. The calculations were done up to the complete basis set (CBS) limit for the CCSD(T) method. Molecular structures of many low-energy conformers/isomers were located. Brønsted acidities in the gas phase and pKa values in aqueous solution were predicted for MO3-m(OH)2m (m = 1-3) and MnO3n-1(OH)2 (n = 2-4). In addition, Brønsted basicities and Lewis acidities (fluoride affinities) were predicted for MO3-m(OH)2m (m = 1-3) as well as the metal oxide clusters MnO3n (n = 1-3). The metal hydroxides were predicted to be strong Brønsted acids and weak to modest Brønsted bases and Lewis acids. The pKa values can have values as negative as -31. Potential energy surfaces for the hydrolysis of the MnO3n (n = 1-4) clusters were calculated. Heats of formation of the metal hydroxides were predicted from the calculated reaction energies, and the agreement with the limited available experimental data is good. The first hydrolysis step leading to the formation of MnO3n-1(OH)2 was predicted to be exothermic, with the exothermicity becoming less negative as n increases and essentially converged at n = 3. Reaction rate constants for the hydrogen transfer steps were calculated using transition state theory and RRKM theory. Further hydrolysis of MnO3n-1(OH)2 tends to be endothermic especially for M = Cr. Fifty-five DFT exchange-correlation functionals were benchmarked for the calculations of the reaction energies, complexation energies, and reaction barriers by comparing to our CCSD(T) results. Overall, the DFT results for the potential energy surfaces are semiquantitatively correct, but no single functional works for all processes and all three metals. Among the functionals benchmarked, the wB97, wB97X, B1B95, B97-1, mPW1LYP, and X3LYP functionals have the best

  20. Radiative transitions in metallic nanoclusters

    NASA Astrophysics Data System (ADS)

    Shalin, A. S.

    2008-02-01

    In this article, a new theoretical approach to studying light-scattering characteristics of nanosized objects based on the solution to the Thomas-Fermi equation and quasi-classical approximation is considered. It is shown that the distribution of valence electrons in the volume of metallic clusters exhibits a specific structure of "spatial zones." With the aid of quasi-classical wave functions, expressions for the appropriate dipole moments of the transitions between the ground and excited states are obtained; the behavior of the spectrum of gold clusters depending on their sizes is studied; a comparison with existing experimental data is carried out.

  1. Development of biomimetic catalytic oxidation methods and non-salt methods using transition metal-based acid and base ambiphilic catalysts

    PubMed Central

    MURAHASHI, Shun-Ichi

    2011-01-01

    This review focuses on the development of ruthenium and flavin catalysts for environmentally benign oxidation reactions based on mimicking the functions of cytochrome P-450 and flavoenzymes, and low valent transition-metal catalysts that replace conventional acids and bases. Several new concepts and new types of catalytic reactions based on these concepts are described. PMID:21558760

  2. Vertical Field-Effect Transistor Based on Graphene-Transition Metal Dichalcogenides Heterostructures

    NASA Astrophysics Data System (ADS)

    Kumar, Jatinder; Chien, Hui-Chun; Bellus, Matthew Z.; Sicilian, David L.; Aubin, Davis St.; Chiu, Hsin-Ying; Physics and Astronomy, University of Kansas Team

    2014-03-01

    The remarkable properties of graphene has made it possible to create transistors just few atoms thick. A new development was that the other two-dimensional materials can be stacked on it with atomic layer precision, creating numerous heterostructures on demand. Here, novel vertical field-effect transistor composed of graphene- transition metal dichalcogenides (TMDs) heterostructures is fabricated and characterized at various temperatures. Due to ultrathin nature of these transistors, they present the ultimate limit for electron transport in heterostructures. Tunneling and thermionic transport characteristics are studied among different graphene-TMDs heterostructures. Their electronic properties have been investigated and can be used in vast range of devices.

  3. Increased induction in FeCo-based nanocomposite materials with reduced early transition metal growth inhibitors

    NASA Astrophysics Data System (ADS)

    Miller, K. J.; Leary, A.; Kernion, S. J.; Wise, A.; Laughlin, D. E.; McHenry, M. E.; Keylin, Vladimir; Huth, Joe

    2010-05-01

    We report on new high-saturation induction, high-temperature nanocomposite alloys with reduced glass formers. The amounts of the magnetic transition metals and early transition metal growth inhibitors were systematically varied to determine trade-offs between higher inductions and fine microstructures with consequently lower magnetic losses. Alloys of nominal composition (Fe65Co35)79.5+xNb4-xB13Si2Cu1.5 (x=0-4) were cast into a 28 mm wide, 20 μm thick ribbon from which toroidal cores were wound. Inductions and magnetic losses were measured after nanocrystallization and stress relief. We report technical magnetic properties: permeability, maximum induction, remanence ratio, coercive field, and high frequency magnetic losses as a function of composition and annealing temperature for these alloys. Of note is the development of maximum inductions in excess of 1.76 T in cores made of alloys with the x=4 composition and maximum inductions in excess of 1.67 T in alloys with the x=3 composition, which also exhibit power losses smaller than 10 W/kg at 0.2 T induction levels in 20 kHz fields. We discuss optimization of induction with chemistry and correlate the microstructures with losses.

  4. Combinatorial Search of Hydrogen Catalysts Based on Transition Metal Embedded Graphitic Carbons

    NASA Astrophysics Data System (ADS)

    Choi, Woon Ih; Wood, Brandon; Schwegler, Eric; Ogitsu, Tadashi; Quantum Simulation Group Team

    2015-03-01

    To find right d-orbital configuration for hydrogen catalyst among embedded transition metal (TM) atoms into the lattice of graphene, we performed high-throughput computational search out of 300 combinatorial material pools. Theoretical criteria, so called descriptors regarding material stability and catalytic activity are considered and we were able to narrow down to ten materials for hydrogen evolution, two for hydrogen oxidation reaction. Since catalytically active sites are isolated to single TM atom, Volmer-Kubas type of new reaction pathway is expected for hydrogen evolution. Earth-abundant element Mo, bulk form of which doesn't show good catalytic activity at all, turns into catalytically active site as it is dispersed atomically and its d-orbitals splits by the symmetry of local coordination at the binding sites.

  5. Volume-based considerations for the metal-insulator transition of CMR oxides

    SciTech Connect

    Neumeier, J.J.; Hundley, M.F.; Cornelius, A.L.; Andres, K.

    1998-03-01

    The sensitivity of {rho} [electrical resistivity] to changes in volume which occur through: (1) applied pressure, (2) variations in temperature, and (3) phase transitions, is evaluated for some selected CMR oxides. It is argued that the changes in volume associated with phase changes are large enough to produce self pressures in the range of 0.18 to 0.45 GPa. The extreme sensitivity of the electrical resistivity to pressure indicates that these self pressures are responsible for large features in the electrical resistivity and are an important component for occurrence the metallicity below {Tc}. It is suggested that this is related to a strong volume dependence of the electron phonon coupling in the CMR oxides.

  6. Design, spectral characterization and biological studies of transition metal(II) complexes with triazole Schiff bases

    NASA Astrophysics Data System (ADS)

    Hanif, Muhammad; Chohan, Zahid H.

    2013-03-01

    A new series of three biologically active triazole derived Schiff base ligands L1-L3 have been synthesized in equimolar reaction of 3-amino-1H-1,2,4-triazole with pyrrol-2-carboxaldehyde, 4-bromo-thiophene-2-carboxaldehyde, and 5-iodo-2-hydroxy benzaldehyde. The prepared Schiff bases were used for further complex formation reaction with different metal elements like Co(II), Ni(II), Cu(II) and Zn(II) as chlorides by using a molar ratio of ligand:metal as 2:1. The structure and bonding nature of all the compounds were identified by their physical, spectral and analytical data. All the metal(II) complexes possessed an octahedral geometry except the Cu(II) complexes which showed a distorted octahedral geometry. All the synthesized compounds, were studied for their in vitro antibacterial, and antifungal activities, against four Gram-negative (Escherichia coli, Shigella sonnei, Pseudomonas aeruginosa and Salmonella typhi) and two Gram-positive (Bacillus subtilis and Staphylococcus aureus) bacterial strains and against six fungal strains (Trichophyton longifusus, Candida albicans, Aspergillus flavus, Microsporum canis, Fusarium solani and Candida glabrata) by using agar-well diffusion method. It has been shown that all the synthesized compounds showed moderate to significant antibacterial activity against one or more bacterial strains. In vitro Brine Shrimp bioassay was also carried out to investigate the cytotoxic properties of these compounds. The data also revealed that the metal complexes showed better activity than the ligands due to chelation/coordination.

  7. Design, spectral characterization and biological studies of transition metal(II) complexes with triazole Schiff bases.

    PubMed

    Hanif, Muhammad; Chohan, Zahid H

    2013-03-01

    A new series of three biologically active triazole derived Schiff base ligands L(1)-L(3) have been synthesized in equimolar reaction of 3-amino-1H-1,2,4-triazole with pyrrol-2-carboxaldehyde, 4-bromo-thiophene-2-carboxaldehyde, and 5-iodo-2-hydroxy benzaldehyde. The prepared Schiff bases were used for further complex formation reaction with different metal elements like Co(II), Ni(II), Cu(II) and Zn(II) as chlorides by using a molar ratio of ligand:metal as 2:1. The structure and bonding nature of all the compounds were identified by their physical, spectral and analytical data. All the metal(II) complexes possessed an octahedral geometry except the Cu(II) complexes which showed a distorted octahedral geometry. All the synthesized compounds, were studied for their in vitro antibacterial, and antifungal activities, against four Gram-negative (Escherichia coli, Shigella sonnei, Pseudomonas aeruginosa and Salmonella typhi) and two Gram-positive (Bacillus subtilis and Staphylococcus aureus) bacterial strains and against six fungal strains (Trichophyton longifusus, Candida albicans, Aspergillus flavus, Microsporum canis, Fusarium solani and Candida glabrata) by using agar-well diffusion method. It has been shown that all the synthesized compounds showed moderate to significant antibacterial activity against one or more bacterial strains. In vitro Brine Shrimp bioassay was also carried out to investigate the cytotoxic properties of these compounds. The data also revealed that the metal complexes showed better activity than the ligands due to chelation/coordination. PMID:23277183

  8. Syntheses, crystal structures, anticancer activities of three reduce Schiff base ligand based transition metal complexes

    NASA Astrophysics Data System (ADS)

    Chang, Hui-Qin; Jia, Lei; Xu, Jun; Zhu, Tao-Feng; Xu, Zhou-Qing; Chen, Ru-Hua; Ma, Tie-Liang; Wang, Yuan; Wu, Wei-Na

    2016-02-01

    Three nickel(II) complexes, [Ni2(L1)2(tren)2(H2O)](ClO4)3 (1), [NiL2(tren)2](ClO4)·2.5H2O (2), [NiL2(tren)2]I·1.5H2O·CH3OH (3) based on amino acid reduced Schiff ligands are synthesized and characterized by physico-chemical and spectroscopic methods. The results show that in all complexes, the amino acid ligand is deprotonated and acts as an anionic ligand. In the dinuclear complex 1, each Ni(II) atom has a distorted octahedron geometry while with different coordination environment. However, the complexes 2 and 3 are mononuclear, almost with the same coordination environment. Furthermore, in vitro experiments are carried out, including MTT assay, Annexin V/PI flow cytometry and western blotting, to assess whether the complexes have antitumor effect. And the results show that all the three complexes have moderate anticancer activity towards human hepatic cancer (HepG2), human cervical cancer (HeLa) and human prostate (PC3) cell lines, in a concentration dependent way. The complex 1 exhibit higher cytotoxicity than the other two complexes and can induce human hepatic cancer cell (HepG2) to cell apoptosis by activating caspase 3.

  9. Tetrazole-5-carboxylic acid based salts of earth alkali and transition metal cations.

    PubMed

    Hartdegen, Vera; Klapötke, Thomas M; Sproll, Stefan M

    2009-10-01

    The tetrazole-5-carboxylate anion was investigated as ligand for earth alkali metal and transition metal complexes. Therefore, the strontium 4a (*3 H(2)O, *2.75 H(2)O, *2.5 H(2)O), barium 4b (*3 H(2)O), copper 4c (*3.5 H(2)O, *4 H(2)O), manganese 4d (*4 H(2)O, *5 H(2)O), and silver tetrazol-5-carboxylate 4e (*1.56 H(2)O) were synthesized and characterized by vibrational spectroscopy (IR), and the crystal structures of 4a (*2.75 H(2)O, *2.5 H(2)O), 4b*3 H(2)O, 4c*4 H(2)O, and 4d*5 H(2)O were determined using single crystal X-ray diffraction. The thermal stability was investigated by DSC-measurements, and the sensitivity toward impact and friction was determined by BAM-standards. The copper, strontium, and barium tetrazole-5-carboxyate proved to be suitable thermal and physical stable colorants for pyrotechnic compositions. The crystal structure of the tetragonal modification of strontium tetrazole-5-carboxyate possesses channels along the c-axis, leading to a porous material. PMID:19780625

  10. Highly tunable-emittance radiator based on semiconductor-metal transition of VO2 thin films

    NASA Astrophysics Data System (ADS)

    Hendaoui, Ali; Émond, Nicolas; Chaker, Mohamed; Haddad, Émile

    2013-02-01

    This paper describes a VO2-based smart structure with an emittance that increases with the temperature. A large tunability of the spectral emittance, which can be as high as 0.90, was achieved. The transition of the total emittance with the temperature was fully reversible according to a hysteresis cycle, with a transition temperature of 66.5 °C. The total emittance of the device was found to be 0.22 and 0.71 at 25 °C and 100 °C, respectively. This emittance performance and the structure simplicity are promising for the next generation of energy-efficient cost-effective passive thermal control systems of spacecrafts.

  11. An Ultrasonic Study on the Polyamorphic Transition in La/Ce-based Bulk Metallic Glass to 12 GPa

    NASA Astrophysics Data System (ADS)

    Qi, X.; Wang, X.; Chen, T.; Welch, D. O.; Jiang, J.; Li, B.

    2015-12-01

    Bulk metallic glasses (BMGs), also known as amorphous alloys, are one of the most promising materials in the 21st century. With their unique structures, BMGs are at the cutting edge of materials study for both commercial applications and fundamental studies. In the light of engineering applications, some metal-metal alloy BMGs are stronger than steels but able to be shaped and molded like plastics. As a new member of glass family, metallic glasses are also good models for studies of fundamental problems in condensed matter physics. Pressure-induced polyamorphism in Ce-based bulk metallic glasses have attracted interest in recent years. Ultrasonic measurements of the compressional and shear wave velocities not only provide critical information about their interatomic forces, but also offer a unique approach for precise determination of mass densities under pressure that are quite difficult to access by other methods. In this study, the acoustic velocities of La32Ce32Al16Ni5Cu15 bulk metallic glass were measured up to 12.3 GPa using ultrasonic interferometry in a multi-anvil apparatus at room temperature. Both compressional and shear waves exhibited softening behaviors at 0-4 GPa, followed by a continuous increase (stiffening) with pressures. Measurements under decompression exhibit a hysteretic behavior compared to that on compression. The mass density as a function of pressure revealed three different amorphous states and the transition pressures were accompanied by distinct changes in the pressure derivatives of elastic moduli. The interpretation of the residual densification and the softening/stiffening across the polyamorphic transition can be sought via the topological rearrangement of the solute-centered clusters in medium-range order and the possibility of 4f electron localization/delocalization in Ce.

  12. Synchrotron-based investigation of transition-metal getterability in n-type multicrystalline silicon

    NASA Astrophysics Data System (ADS)

    Morishige, Ashley E.; Jensen, Mallory A.; Hofstetter, Jasmin; Yen, Patricia X. T.; Wang, Chenlei; Lai, Barry; Fenning, David P.; Buonassisi, Tonio

    2016-05-01

    Solar cells based on n-type multicrystalline silicon (mc-Si) wafers are a promising path to reduce the cost per kWh of photovoltaics; however, the full potential of the material and how to optimally process it are still unknown. Process optimization requires knowledge of the response of the metal-silicide precipitate distribution to processing, which has yet to be directly measured and quantified. To supply this missing piece, we use synchrotron-based micro-X-ray fluorescence (μ-XRF) to quantitatively map >250 metal-rich particles in n-type mc-Si wafers before and after phosphorus diffusion gettering (PDG). We find that 820 °C PDG is sufficient to remove precipitates of fast-diffusing impurities and that 920 °C PDG can eliminate precipitated Fe to below the detection limit of μ-XRF. Thus, the evolution of precipitated metal impurities during PDG is observed to be similar for n- and p-type mc-Si, an observation consistent with calculations of the driving forces for precipitate dissolution and segregation gettering. Measurements show that minority-carrier lifetime increases with increasing precipitate dissolution from 820 °C to 880 °C PDG, and that the lifetime after PDG at 920 °C is between the lifetimes achieved after 820 °C and 880 °C PDG.

  13. Exploring the DNA binding mode of transition metal based biologically active compounds

    NASA Astrophysics Data System (ADS)

    Raman, N.; Sobha, S.

    2012-01-01

    Few novel 4-aminoantipyrine derived Schiff bases and their metal complexes were synthesized and characterized. Their structural features and other properties were deduced from the elemental analysis, magnetic susceptibility and molar conductivity as well as from mass, IR, UV-vis, 1H NMR and EPR spectral studies. The binding of the complexes with CT-DNA was analyzed by electronic absorption spectroscopy, viscosity measurement, and cyclic voltammetry. The interaction of the metal complexes with DNA was also studied by molecular modeling with special reference to docking. The experimental and docking results revealed that the complexes have the ability of interaction with DNA of minor groove binding mode. The intrinsic binding constants ( Kb) of the complexes with CT-DNA were found out which show that they are minor groove binders. Gel electrophoresis assay demonstrated the ability of the complexes to cleave the pUC19 DNA in the presence of AH 2 (ascorbic acid). Moreover, the oxidative cleavage studies using distamycin revealed the minor groove binding for the newly synthesized 4-aminoantipyrine derived Schiff bases and their metal complexes. Evaluation of antibacterial activity of the complexes against Staphylococcus aureus, Pseudomonas aeruginosa, Escherichia coli, Staphylococcus epidermidis, and Klebsiella pneumoniae exhibited that the complexes have potent biocidal activity than the free ligands.

  14. Adsorption of gas molecules on transition metal embedded graphene: a search for high-performance graphene-based catalysts and gas sensors

    NASA Astrophysics Data System (ADS)

    Zhou, Miao; Lu, Yun-Hao; Cai, Yong-Qing; Zhang, Chun; Feng, Yuan-Ping

    2011-09-01

    We report an investigation on the adsorption of small gas molecules (O2, CO, NO2 and NH3) on pristine and various transition metal embedded graphene samples using a first-principles approach based on density-functional theory (DFT). The most stable adsorption geometry, energy, charge transfer, and magnetic moment of these molecules on graphene embedded with different transition metal elements are thoroughly discussed. Our calculations found that embedded transition metal elements in general can significantly enhance the interactions between gas molecules and graphene, and for applications of graphene-based catalysis, Ti and Au may be the best choices among all transition metal elements. We also expect a detailed analysis of the electronic structures and magnetic properties of these systems to shed light on future applications of graphene-based gas sensing and spintronics.

  15. Metal-metal bond lengths in complexes of transition metals*

    PubMed Central

    Pauling, Linus

    1976-01-01

    In complexes of the transition metals containing clusters of metal atoms the cobalt-cobalt bond lengths are almost always within 1 pm of the single-bond value 246 pm given by the enneacovalent radius of cobalt, whereas most of the observed iron-iron bond lengths are significantly larger than the single-bond value 248 pm, the mean being 264 pm, which corresponds to a half-bond. A simple discussion of the structures of these complexes based on spd hybrid orbitals, the electroneutrality principle, and the partial ionic character of bonds between unlike atoms leads to the conclusion that resonance between single bonds and no-bonds would occur for iron and its congeners but not for cobalt and its congeners, explaining the difference in the bond lengths. PMID:16592368

  16. DFT based study of transition metal nano-clusters for electrochemical NH3 production.

    PubMed

    Howalt, J G; Bligaard, T; Rossmeisl, J; Vegge, T

    2013-05-28

    Theoretical studies of the possibility of producing ammonia electrochemically at ambient temperature and pressure without direct N2 dissociation are presented. Density functional theory calculations were used in combination with the computational standard hydrogen electrode to calculate the free energy profile for the reduction of N2 admolecules and N adatoms on transition metal nanoclusters in contact with an acidic electrolyte. This work has established linear scaling relations for the dissociative reaction intermediates NH, NH2, and NH3. In addition, linear scaling relations for the associative reaction intermediates N2H, N2H2, and N2H3 have been determined. Furthermore, correlations between the adsorption energies of N, N2, and H have been established. These scaling relations and the free energy corrections are used to establish volcanoes describing the onset potential for electrochemical ammonia production and hence describe the potential determining steps for the electrochemical ammonia production. The competing hydrogen evolution reaction has also been analyzed for comparison. PMID:23598667

  17. Durability study of transition metal based non-precious cathode in PEFC

    SciTech Connect

    Wu, Gang; Zelenay, Piotr

    2009-01-01

    This paper focuses on performance durability of newly developed polyaniline (PANI)-derived non-precious cathode catalyst, whose high oxygen-reduction activity was verified in electrochemical and fuel cell testing, exhibiting onset and half-wave potential (E{sup 1/2}) of oxygen reduction at 0.90 V and 0.77 V, respectively, as well as an insignificant H{sub 2}O{sub 2} yields below 1%. It was found catalyst durability in fuel cell life tests is greatly dependent on the catalyst synthesis including nitrogen precursors, employed transition metals, and supporting materials. Importantly, the working voltages in fuel cell testing have a profound impact on the stability, which much more stable performance can be observed at lower voltage such as 0.4 V when compared with higher voltage, 0.6 V. Preliminary physical and electrochemical characterization present to provide insight into the origin of the possible degradation mechanism for the non-precious active sites.

  18. Estimation of Enthalpy of Formation of Liquid Transition Metal Alloys: A Modified Prescription Based on Macroscopic Atom Model of Cohesion

    NASA Astrophysics Data System (ADS)

    Raju, Subramanian; Saibaba, Saroja

    2016-09-01

    The enthalpy of formation Δo H f is an important thermodynamic quantity, which sheds significant light on fundamental cohesive and structural characteristics of an alloy. However, being a difficult one to determine accurately through experiments, simple estimation procedures are often desirable. In the present study, a modified prescription for estimating Δo H f L of liquid transition metal alloys is outlined, based on the Macroscopic Atom Model of cohesion. This prescription relies on self-consistent estimation of liquid-specific model parameters, namely electronegativity ( ϕ L) and bonding electron density ( n b L ). Such unique identification is made through the use of well-established relationships connecting surface tension, compressibility, and molar volume of a metallic liquid with bonding charge density. The electronegativity is obtained through a consistent linear scaling procedure. The preliminary set of values for ϕ L and n b L , together with other auxiliary model parameters, is subsequently optimized to obtain a good numerical agreement between calculated and experimental values of Δo H f L for sixty liquid transition metal alloys. It is found that, with few exceptions, the use of liquid-specific model parameters in Macroscopic Atom Model yields a physically consistent methodology for reliable estimation of mixing enthalpies of liquid alloys.

  19. Estimation of Enthalpy of Formation of Liquid Transition Metal Alloys: A Modified Prescription Based on Macroscopic Atom Model of Cohesion

    NASA Astrophysics Data System (ADS)

    Raju, Subramanian; Saibaba, Saroja

    2016-07-01

    The enthalpy of formation Δo H f is an important thermodynamic quantity, which sheds significant light on fundamental cohesive and structural characteristics of an alloy. However, being a difficult one to determine accurately through experiments, simple estimation procedures are often desirable. In the present study, a modified prescription for estimating Δo H {f/L} of liquid transition metal alloys is outlined, based on the Macroscopic Atom Model of cohesion. This prescription relies on self-consistent estimation of liquid-specific model parameters, namely electronegativity (ϕ L) and bonding electron density (n {b/L}). Such unique identification is made through the use of well-established relationships connecting surface tension, compressibility, and molar volume of a metallic liquid with bonding charge density. The electronegativity is obtained through a consistent linear scaling procedure. The preliminary set of values for ϕ L and n {b/L}, together with other auxiliary model parameters, is subsequently optimized to obtain a good numerical agreement between calculated and experimental values of Δo H {f/L} for sixty liquid transition metal alloys. It is found that, with few exceptions, the use of liquid-specific model parameters in Macroscopic Atom Model yields a physically consistent methodology for reliable estimation of mixing enthalpies of liquid alloys.

  20. Transition metals in superheat melts

    NASA Technical Reports Server (NTRS)

    Jakes, Petr; Wolfbauer, Michael-Patrick

    1993-01-01

    A series of experiments with silicate melts doped with transition element oxides was carried out at atmospheric pressures of inert gas at temperatures exceeding liquidus. As predicted from the shape of fO2 buffer curves in T-fO2 diagrams the reducing conditions for a particular oxide-metal pair can be achieved through the T increase if the released oxygen is continuously removed. Experimental studies suggest that transition metals such as Cr or V behave as siderophile elements at temperatures exceeding liquidus temperatures if the system is not buffered by the presence of other oxide of more siderophile element. For example the presence of FeO prevents the reduction of Cr2O3. The sequence of decreasing siderophility of transition elements at superheat conditions (Mo, Ni, Fe, Cr) matches the decreasing degree of depletion of siderophile elements in mantle rocks as compared to chondrites.

  1. Derivatives of phosphate Schiff base transition metal complexes: synthesis, studies and biological activity

    NASA Astrophysics Data System (ADS)

    El-Wahab, Z. H. Abd; El-Sarrag, M. R.

    2004-01-01

    We report the synthesis and structural characterization of series of tetra- and hexacoordinate metal chelate complexes of phosphate Schiff base ligands having the general composition LMX n·H 2O and L 2MX n (L=phosphate Schiff base ligand; M=Ag +, Mn 2+, Cu 2+, Zn 2+, Cd 2+, Hg 2+, or Fe 3+ and X=NO 3-, Br - or Cl -). The structure of the prepared compounds was investigated using elemental analysis, IR, 1H and 31P NMR, UV-vis, mass spectra, solid reflectance, magnetic susceptibility and conductance measurements as well as conductometric titration. In all the complexes studied, the ligands act as a chelate ligand with coordination involving the phosphateO-atom and the azomethineN-atom. IR, solid reflectance spectra and magnetic moment measurement are used to infer the structure and to illustrate the coordination capacity of ligand. IR spectra show the presence of coordinated nitrate and water molecule, the magnetic moments of all complexes show normal magnetic behavior and the electronic spectra of the metal complexes indicate a tetra- and octahedral structure for Mn 2+, octahedral structure of Fe 3+ and both square-planar and distorted octahedral structure for Cu 2+ complexes. Antimicrobial activity of the ligands and their complexes were tested using the disc diffusion method and the chosen strains include Staphylococcus aureus, Pseudomonas aereuguinosa, Klebsiella penumoniae, Escherichia coli, Microsporum canis, Trichophyton mentagrophyte and Trichophyton rubrum. Some known antibiotics are included for the sake of comparison and the chosen antibiotic are Amikacin, Doxycllin, Augmantin, Sulperazon, Unasyn, Septrin, Cefobid, Ampicillin, Nitrofurantion, Traivid and Erythromycin.

  2. Molten salt extraction process for the recovery of valued transition metals from land-based and deep-sea minerals

    DOEpatents

    Maroni, Victor A.; von Winbush, Samuel

    1988-01-01

    A process for extracting transition metals and particularly cobalt and manganese together with iron, copper and nickel from low grade ores (including ocean-floor nodules) by converting the metal oxides or other compositions to chlorides in a molten salt, and subsequently using a combination of selective distillation at temperatures below about 500.degree. C., electrolysis at a voltage not more negative than about -1.5 volt versus Ag/AgCl, and precipitation to separate the desired manganese and cobalt salts from other metals and provide cobalt and manganese in metallic forms or compositions from which these metals may be more easily recovered.

  3. Molten salt extraction process for the recovery of valued transition metals from land-based and deep-sea minerals

    DOEpatents

    Maroni, V.A.; von Winbush, S.

    1987-05-01

    A process for extracting transition metals and particularly cobalt and manganese together with iron, copper and nickel from low grade ores (including ocean-floor nodules) by converting the metal oxides or other compositions to chlorides in a molten salt, and subsequently using a combination of selective distillation at temperatures below about 500/degree/C, electrolysis at a voltage not more negative that about /minus/1.5 volt versus Ag/AgCl, and precipitation to separate the desired manganese and cobalt salts from other metals and provide cobalt and manganese in metallic forms or compositions from which these metals may be more easily recovered.

  4. Immobilized transition metal-based radical scavengers and their effect on durability of Aquivion® perfluorosulfonic acid membranes

    NASA Astrophysics Data System (ADS)

    D'Urso, C.; Oldani, C.; Baglio, V.; Merlo, L.; Aricò, A. S.

    2016-01-01

    A simple and broadly applicable preparation procedure to obtain silica-supported transition metal (namely Cr, Co and Mn)-based radical scavengers, containing sulfonic acid functionalities, is reported. These systems are widely characterised in terms of structure, bulk and surface composition and morphology by X-Ray Diffraction (XRD), X-Ray Fluorescence (XRF), X-Ray Photoelectron Spectroscopy (XPS) and Transmission Electron Microscopy (TEM). The scavenger material is loaded in ePTFE reinforced membranes prepared from Aquivion® perfluorosulfonic acid (PFSA) dispersions. All these composite membranes show longer lifetime in Accelerated Stress Tests (AST) and reduced fluoride release in Fenton's tests than the scavenger-free membranes without any loss in electrochemical performance. The Cr-scavenger-based polymer electrolyte shows a three-time larger stability than the pristine membrane.

  5. Dilute magnetic semiconductors based on wide bandgap SiO 2 with and without transition metal elements

    NASA Astrophysics Data System (ADS)

    Dinh, Van An; Sato, Kazunori; Katayama-Yoshida, Hiroshi

    2005-10-01

    Material designs based on the first principle calculations of electronic structures are proposed for α-quartz SiO 2-based dilute magnetic semiconductors. The incorporation of transition metals (TMs) into Si sites and of the non-TM atoms into O sites are treated for various concentrations. At temperatures higher than room temperature, most of the TM-doped SiO 2 have no magnetism, yet Si 1- xMn xO 2 might achieve the ferromagnetism. The substitution of O by non-TM atoms as C or N also induces the magnetism in the host. However, while the N's substitution induces the ferromagnetism, C's substitution causes an anti-ferromagnetic behavior in the host material SiO 2.

  6. Transition-metal-based magnetic refrigerants for room-temperature applications.

    PubMed

    Tegus, O; Brück, E; Buschow, K H J; de Boer, F R

    2002-01-10

    Magnetic refrigeration techniques based on the magnetocaloric effect (MCE) have recently been demonstrated as a promising alternative to conventional vapour-cycle refrigeration. In a material displaying the MCE, the alignment of randomly oriented magnetic moments by an external magnetic field results in heating. This heat can then be removed from the MCE material to the ambient atmosphere by heat transfer. If the magnetic field is subsequently turned off, the magnetic moments randomize again, which leads to cooling of the material below the ambient temperature. Here we report the discovery of a large magnetic entropy change in MnFeP0.45As0.55, a material that has a Curie temperature of about 300 K and which allows magnetic refrigeration at room temperature. The magnetic entropy changes reach values of 14.5 J K-1 kg-1 and 18 J K-1 kg-1 for field changes of 2 T and 5 T, respectively. The so-called giant-MCE material Gd5Ge2Si2 (ref. 2) displays similar entropy changes, but can only be used below room temperature. The refrigerant capacity of our material is also significantly greater than that of Gd (ref. 3). The large entropy change is attributed to a field-induced first-order phase transition enhancing the effect of the applied magnetic field. PMID:11805828

  7. Gas sorption and transition-metal cation separation with a thienothiophene based zirconium metal-organic framework

    NASA Astrophysics Data System (ADS)

    SK, Mostakim; Grzywa, Maciej; Volkmer, Dirk; Biswas, Shyam

    2015-12-01

    The modulated synthesis of the thienothiophene based zirconium metal-organic framework (MOF) material having formula [Zr6O4(OH)4(DMTDC)6]·4.8DMF·10H2O (1) (H2DMTDC=3,4-dimethylthieno[2,3-b]thiophene-2,5-dicarboxylic acid; DMF=N,N'-dimethylformamide) was carried out by heating a mixture of ZrCl4, H2DMTDC linker and benzoic acid (used as a modulator) with a molar ratio of 1:1:30 in DMF at 150 °C for 24 h. Systematic investigations have been performed in order to realize the effect of ZrCl4/benzoic acid molar ratio on the crystallinity of the material. The activation (i.e., the removal of the guest solvent molecules from the pores) of as-synthesized compound was achieved by stirring it with methanol and subsequently heating under vacuum. A combination of X-ray diffraction (XRD), Fourier transform infrared (FT-IR), thermogravimetric (TG) and elemental analysis was used to examine the phase purity of the as-synthesized and thermally activated 1. The material displays high thermal stability up to 310 °C in an air atmosphere. As revealed from the XRD measurements, the compound retains its crystallinity when treated with water, acetic acid and 1 M HCl solutions. The N2 and CO2 sorption analyses suggest that the material possesses remarkably high microporosity (SBET=1236 m2 g-1; CO2 uptake=3.5 mmol g-1 at 1 bar and 0 °C). The compound also shows selective adsorption behavior for Cu2+ over Co2+ and Ni2+ ions.

  8. Redox, thermodynamic and spectroscopic of some transition metal complexes containing heterocyclic Schiff base ligands

    NASA Astrophysics Data System (ADS)

    Abu-Hussen, Azza A. A.; Linert, Wolfgang

    2009-09-01

    Complexes of two series of Schiff base ligands, H 2L a and H 2L b derived from the reaction of 2,6-diacetyl pyridine with semicarbazide, H 2L a and thiosemicarbazide, H 2L b, with the metal ions, Co(II), Ni(II), Cu(II), VO(IV) and UO 2(VI) have been prepared. The ligands are characterized by elemental analysis, IR, UV-vis and 1H NMR. The structures of the complexes are investigated with the IR, UV-vis, X-band ESR spectra, 1H NMR and thermal gravimetric analysis as well as conductivity and magnetic moment measurements. The IR-spectra reveal the presence of variable modes of chelation for the investigated ligands. A variety of binuclear or mononuclear complexes were obtained with the two ligands in tri-, tetra or pentadentate forms. The bonding sites are the pyridine nitrogen, two azomethine nitrogen atoms and ketonic oxygen in case of H 2L a or sulphur atoms in case of H 2L b. The Coats-Redfern equation has been used to calculate the kinetic and thermodynamic parameters for the different thermal decomposition steps of some complexes. Cyclic voltammograms of Co(II) and Ni(II) show quasi-reversible peaks. The redox properties and the nature of the electro-active species of the complexes have been characterized.

  9. Density functional theory study of interaction, bonding and affinity of group IIb transition metal cations with nucleic acid bases

    NASA Astrophysics Data System (ADS)

    Bagchi, Sabyasachi; Mandal, Debasish; Ghosh, Deepanwita; Das, Abhijit K.

    2012-05-01

    The structure, bonding, and energetics of the complexes obtained from the interaction between the most stable tautomeric forms of free DNA and RNA bases and Zn2+, Cd2+ and Hg2+ cations have been studied using density functional B3LYP method. The 6-311+G (2df, 2p) basis set along with LANL2DZ pseudopotentials for the cations are used in the calculations. The tautomerization paths of the nucleobases are investigated and transition states between the tautomeric forms of the free bases are located. The relative stability of the complexes and the tautomers of the free nucleobases are discussed referring to MIA and relative energy values. For uracil, thymine and adenine, interaction of the metal cations with the most stable tautomers form the least stable molecular complexes. For cytosine and guanine, the stability of the metalated complexes differs significantly. The enthalpy (ΔH), entropy (TΔS) and free energy (ΔG) of the complexes at 298 K have also been calculated.

  10. Approximating metal-insulator transitions

    NASA Astrophysics Data System (ADS)

    Danieli, Carlo; Rayanov, Kristian; Pavlov, Boris; Martin, Gaven; Flach, Sergej

    2015-12-01

    We consider quantum wave propagation in one-dimensional quasiperiodic lattices. We propose an iterative construction of quasiperiodic potentials from sequences of potentials with increasing spatial period. At each finite iteration step, the eigenstates reflect the properties of the limiting quasiperiodic potential properties up to a controlled maximum system size. We then observe approximate Metal-Insulator Transitions (MIT) at the finite iteration steps. We also report evidence on mobility edges, which are at variance to the celebrated Aubry-André model. The dynamics near the MIT shows a critical slowing down of the ballistic group velocity in the metallic phase, similar to the divergence of the localization length in the insulating phase.

  11. Synthesis of transition metal carbonitrides

    DOEpatents

    Munir, Zuhair A. R.; Eslamloo-Grami, Maryam

    1994-01-01

    Transition metal carbonitrides (in particular, titanium carbonitride, TiC.sub.0.5 N.sub.0.5) are synthesized by a self-propagating reaction between the metal (e.g., titanium) and carbon in a nitrogen atmosphere. Complete conversion to the carbonitride phase is achieved with the addition of TiN as diluent and with a nitrogen pressure .gtoreq.0.6 MPa. Thermodynamic phase-stability calculations and experimental characterizations of quenched samples provided revealed that the mechanism of formation of the carbonitride is a two-step process. The first step involves the formation of the nonstoichiometric carbide, TiC.sub.0.5, and is followed by the formation of the product by the incorporation of nitrogen in the defect-structure carbide.

  12. Pseudopotential-Based Correlation Consistent Composite Approach (rp-ccCA) for First- and Second-Row Transition Metal Thermochemistry.

    PubMed

    Manivasagam, Sivabalan; Laury, Marie L; Wilson, Angela K

    2015-07-01

    The relativistic-pseudopotential correlation consistent composite approach (rp-ccCA) was used to determine the enthalpy of formation (ΔHf) of 24 first row (3d) transition metal compounds. The rp-ccCA-derived ΔHf's were compared to ΔHf's previously obtained with an all-electron composite method for transition metals (ccCA-TM). For the 3d metal systems, rp-ccCA achieves transition metal accuracy, within 3 kcal/mol of reliable experimental data, overall. By utilizing pseudopotentials within the rp-ccCA methodology, we observed a significant computational time savings (53%) in comparison to the all-electron basis sets employed within ccCA-TM. With the proven reliability and accuracy of rp-ccCA, the methodology was employed to construct a calibration set of 210 second-row (4d) transition metal compounds and their ΔHf's. The 4d calibration set is referred to as 4dHf-210. Within the 4dHf-210 set, there were 61 molecules with available experimental data. The average experimental uncertainty was 4.05 kcal/mol and the mean absolute deviation of rp-ccCA was 3.64 kcal/mol, excluding outliers (10 total). This study provides a large set of energetics that can be used to gauge existing and future computational methodologies and to aid experimentalists in reaction design. PMID:26000954

  13. Efficient Thermal-Light Interconversions Based on Optical Topological Transition in the Metal-Dielectric Multilayered Metamaterials.

    PubMed

    Zhou, Jing; Chen, Xi; Guo, L Jay

    2016-04-01

    Metal-dielectric multilayered metamaterials are proposed to work as wideband spectral-selective emitters/absorbers due to the topological change in isofrequency contour around the epsilon-near-zero point. By setting the transition at the border between the visible and IR ranges, the metal-dielectric multilayered metamaterials become good absorbers/emitters for visible light and good reflectors for IR light, which are desirable for efficient thermal-light interconversions. PMID:26891165

  14. Recent progress in high performance and reliable n-type transition metal oxide-based thin film transistors

    NASA Astrophysics Data System (ADS)

    Kwon, Jang Yeon; Kyeong Jeong, Jae

    2015-02-01

    This review gives an overview of the recent progress in vacuum-based n-type transition metal oxide (TMO) thin film transistors (TFTs). Several excellent review papers regarding metal oxide TFTs in terms of fundamental electron structure, device process and reliability have been published. In particular, the required field-effect mobility of TMO TFTs has been increasing rapidly to meet the demands of the ultra-high-resolution, large panel size and three dimensional visual effects as a megatrend of flat panel displays, such as liquid crystal displays, organic light emitting diodes and flexible displays. In this regard, the effects of the TMO composition on the performance of the resulting oxide TFTs has been reviewed, and classified into binary, ternary and quaternary composition systems. In addition, the new strategic approaches including zinc oxynitride materials, double channel structures, and composite structures have been proposed recently, and were not covered in detail in previous review papers. Special attention is given to the advanced device architecture of TMO TFTs, such as back-channel-etch and self-aligned coplanar structure, which is a key technology because of their advantages including low cost fabrication, high driving speed and unwanted visual artifact-free high quality imaging. The integration process and related issues, such as etching, post treatment, low ohmic contact and Cu interconnection, required for realizing these advanced architectures are also discussed.

  15. Colorimetric recognition of different enzymology-concerning transition metals based on a hybrid cluster complex.

    PubMed

    Li, Shun-Hua; Yuan, Wen-Tao; Zheng, Hong; Xu, Jin-Gou

    2004-07-01

    A hybrid cluster complex, formed by chelating a chromogenic ligand to a [2Fe-2S] cluster, sensitively exhibited differential colorimetric responses towards Hg2+, Cd2+, Cr3+, Pb2, Sn2+, Cu2+, Zn2+, Fe3+ and Co2+ in water at physiological pH. Speciation of some of these metal elements, such as Cr(III) and Sn(IV), was also studied by UV/Vis absorption. PMID:15293390

  16. Mechanical properties, glass transition temperature, and bond enthalpy trends of high metalloid Fe-based bulk metallic glasses

    SciTech Connect

    Gu, X. J.; Poon, S. Joseph; Shiflet, Gary J.; Widom, Michael

    2008-04-21

    Mechanical properties and glass transition temperatures (T{sub g}) of Fe-Cr-Mo-P-C-B bulk metallic glasses containing up to 27 at. % metalloids have been studied. The shear modulus (G) is found to decrease with increasing metalloid content and a maximum plastic strain of {approx}3% is obtained, despite the increase in the number of strong metal-metalloid bonds. Also, T{sub g} increases with the decrease in G, in contrast to usual behavior. By employing first-principles calculations, the results are discussed in light of atomic bonding and connectivity in the amorphous network. The findings are relevant to understanding ductility and glass transition of metallic glasses.

  17. Magnetism and electronic phase transitions in monoclinic transition metal dichalcogenides with transition metal atoms embedded

    NASA Astrophysics Data System (ADS)

    Lin, Xianqing; Ni, Jun

    2016-08-01

    First-principles calculations have been performed to study the energetic, electronic, and magnetic properties of substitutional 3d transition metal dopants in monoclinic transition metal dichalcogenides (TMDs) as topological insulators ( 1 T ' - MX 2 with M = (Mo, W) and X = (S, Se)). We find various favorite features in these doped systems to introduce magnetism and other desirable electronic properties: (i) The Mn embedded monoclinic TMDs are magnetic, and the doped 1 T ' - MoS 2 still maintains the semiconducting character with high concentration of Mn, while an electronic phase transition occurs in other Mn doped monoclinic TMDs with an increasing concentration of Mn. Two Mn dopants prefer the ferromagnetic coupling except for substitution of the nearest Mo atoms in 1 T ' - MoS 2 , and the strength of exchange interaction shows anisotropic behavior with dopants along one Mo zigzag chain having much stronger coupling. (ii) The substitutional V is a promising hole dopant, which causes little change to the energy dispersion around the conduction and valence band edges in most systems. In contrast, parts of the conduction band drop for the electron dopants Co and Ni due to the large structural distortion. Moreover, closing band gaps of the host materials are observed with increasing carrier concentration. (iii) Single Fe dopant has a magnetic moment, but it also dopes electrons. When two Fe dopants have a small distance, the systems turn into nonmagnetic semiconductors. (iv) The formation energies of all dopants are much lower than those in hexagonal TMDs and are all negative in certain growth conditions, suggesting possible realization of the predicted magnetism, electronic phase transitions as well as carrier doping in 1 T ' - MX 2 based topological devices.

  18. Elution of uranium and transition metals from amidoxime-based polymer adsorbents for sequestering uranium from seawater

    DOE PAGESBeta

    Pan, Horng-Bin; Kuo, Li-Jung; Miyamoto, Naomi; Wood, Jordana; Strivens, Jonathan E.; Gill, Gary; Janke, Christopher James; Wai, Chien

    2015-11-30

    High-surface-area amidoxime and carboxylic acid grafted polymer adsorbents developed at Oak Ridge National Laboratory were tested for sequestering uranium in a flowing seawater flume system at the PNNL-Marine Sciences Laboratory. FTIR spectra indicate that a KOH conditioning process is necessary to remove the proton from the carboxylic acid and make the sorbent effective for sequestering uranium from seawater. The alkaline conditioning process also converts the amidoxime groups to carboxylate groups in the adsorbent. Both Na2CO3 H2O2 and hydrochloric acid elution methods can remove ~95% of the uranium sequestered by the adsorbent after 42 days of exposure in real seawater. Themore » Na2CO3 H2O2 elution method is more selective for uranium than conventional acid elution. Iron and vanadium are the two major transition metals competing with uranium for adsorption to the amidoxime-based adsorbents in real seawater. Tiron (4,5-Dihydroxy-1,3-benzenedisulfonic acid disodium salt, 1 M) can remove iron from the adsorbent very effectively at pH around 7. The coordination between vanadium (V) and amidoxime is also discussed based on our 51V NMR data.« less

  19. Elution of uranium and transition metals from amidoxime-based polymer adsorbents for sequestering uranium from seawater

    SciTech Connect

    Pan, Horng-Bin; Kuo, Li-Jung; Miyamoto, Naomi; Wood, Jordana; Strivens, Jonathan E.; Gill, Gary; Janke, Christopher James; Wai, Chien

    2015-11-30

    High-surface-area amidoxime and carboxylic acid grafted polymer adsorbents developed at Oak Ridge National Laboratory were tested for sequestering uranium in a flowing seawater flume system at the PNNL-Marine Sciences Laboratory. FTIR spectra indicate that a KOH conditioning process is necessary to remove the proton from the carboxylic acid and make the sorbent effective for sequestering uranium from seawater. The alkaline conditioning process also converts the amidoxime groups to carboxylate groups in the adsorbent. Both Na2CO3 H2O2 and hydrochloric acid elution methods can remove ~95% of the uranium sequestered by the adsorbent after 42 days of exposure in real seawater. The Na2CO3 H2O2 elution method is more selective for uranium than conventional acid elution. Iron and vanadium are the two major transition metals competing with uranium for adsorption to the amidoxime-based adsorbents in real seawater. Tiron (4,5-Dihydroxy-1,3-benzenedisulfonic acid disodium salt, 1 M) can remove iron from the adsorbent very effectively at pH around 7. The coordination between vanadium (V) and amidoxime is also discussed based on our 51V NMR data.

  20. Synthesis and antioxidant activities of transition metal complexes based 3-hydroxysalicylaldehyde-S-methylthiosemicarbazone

    NASA Astrophysics Data System (ADS)

    Bal-Demirci, Tülay; Şahin, Musa; Kondakçı, Esin; Özyürek, Mustafa; Ülküseven, Bahri; Apak, Reşat

    2015-03-01

    The nickel(II), iron(III), oxovanadium(IV) complexes of the 3-hydroxysalicylidene-S-methyl-thiosemicarbazone (L) were obtained from the 3-hydroxysalicyldehyde-S-methylthiosemicarbazone with the R1-substituted-salicylaldehyde (R1: H, 3-OH) in the presence of Ni(II), Fe(III), VO(IV) as template ion. The ligand and its complexes were characterized by elemental analysis, electronic, UV/Vis., 1H NMR, EPR and IR studies. The free ligand and its metal complexes have been tested for in vitro antioxidant capacity by reduction of copper(II) neocuproine (Cu(II)-Nc) using the CUPRAC method. The ligand exhibited more potent in vitro antioxidant capacity than its complexes. The obtained trolox equivalent antioxidant capacity (TEAC) value of the iron(III) complex (TEACCUPRAC = 3.27) was higher than those of other complexes. Furthermore, the antioxidant activity of the free ligand and its complexes were determined by in vitro methods measuring the scavenging activity of reactive oxygen species (ROS) including hydroxyl radical (radOH), superoxide anion radical (O2rad -), and hydrogen peroxide (H2O2), showing that especially the V(IV) and Fe(III) complexes had significant scavenging activity for ROS.

  1. Synthesis and antioxidant activities of transition metal complexes based 3-hydroxysalicylaldehyde-S-methylthiosemicarbazone.

    PubMed

    Bal-Demirci, Tülay; Şahin, Musa; Kondakçı, Esin; Özyürek, Mustafa; Ülküseven, Bahri; Apak, Reşat

    2015-03-01

    The nickel(II), iron(III), oxovanadium(IV) complexes of the 3-hydroxysalicylidene-S-methyl-thiosemicarbazone (L) were obtained from the 3-hydroxysalicyldehyde-S-methylthiosemicarbazone with the R1-substituted-salicylaldehyde (R1: H, 3-OH) in the presence of Ni(II), Fe(III), VO(IV) as template ion. The ligand and its complexes were characterized by elemental analysis, electronic, UV/Vis., (1)HNMR, EPR and IR studies. The free ligand and its metal complexes have been tested for in vitro antioxidant capacity by reduction of copper(II) neocuproine (Cu(II)-Nc) using the CUPRAC method. The ligand exhibited more potent in vitro antioxidant capacity than its complexes. The obtained trolox equivalent antioxidant capacity (TEAC) value of the iron(III) complex (TEACCUPRAC=3.27) was higher than those of other complexes. Furthermore, the antioxidant activity of the free ligand and its complexes were determined by in vitro methods measuring the scavenging activity of reactive oxygen species (ROS) including hydroxyl radical (OH), superoxide anion radical (O2(-)), and hydrogen peroxide (H2O2), showing that especially the V(IV) and Fe(III) complexes had significant scavenging activity for ROS. PMID:25467658

  2. Synthesis and characterization of three-dimensional transition metal ions doped zinc oxide based dilute magnetic semiconductor thin films

    NASA Astrophysics Data System (ADS)

    Samanta, Kousik

    Dilute magnetic semiconductors (DMS), especially 3d-transition metal (TM) doped ZnO based DMS materials are the most promising candidates for optoelectronics and spintronics applications; e.g. in spin light emitting diode (SLED), spin transistors, and spin field effect transistors (SFET), etc. In the present dissertation, thin films of Zn1-xTMxO (TM = Co2+, Cu2+, and Mn2+) were grown on (0001) oriented Al2O3 substrates by pulsed laser deposition (PLD) technique. The films were highly c-axis oriented, nearly single crystalline, and defects free for a limited concentration of the dilution of transition metal ions. In particular, we have obtained single crystalline phases of Zn1-xTMxO thin films for up to 10, 3, and 5 stoichiometric percentages of Co2+, Cu2+, and Mn2+ respectively. Raman micro-probe system was used to understand the structural and lattice dynamical properties at different physical conditions. The confinement of optical phonons in the disorder lattice was explained by alloy potential fluctuation (APF) using a spatial correlation (SC) model. The detailed analysis of the optical phonon behavior in disorder lattice confirmed the substitution of the transition metal ions in Zn 2+ site of the ZnO host lattice. The secondary phases of ZnCo 2O4, CuO, and ZnMn2O4 were detected in higher Co, Cu, and Mn doped ZnO thin films respectively; where as, XRD did not detect these secondary phases in the same samples. Room temperature ferromagnetism was observed in Co2+ and Cu2+ ions doped ZnO thin films with maximum saturation magnetization (Ms) of 1.0 and 0.76 muB respectively. The origin of the observed ferromagnetism in Zn1-xCoxO thin films was tested by the controlled introduction of shallow donors (Al) in Zn0.9-x Co0.1O:Alx (x = 0.005 and 0.01) thin films. The saturation magnetization for the 10% Co-doped ZnO (1.0 muB /Co) at 300K reduced (˜0.25 muB/Co) due to Al doping. The observed ferromagnetism and the reduction due to Al doping can be explained by the Bound

  3. Complexity in Transition Metal Oxides

    NASA Astrophysics Data System (ADS)

    Dagotto, Elbio; Alvarez, Gonzalo; Moreo, Adriana

    2004-03-01

    Recent computational results in the context of models for manganites and cuprates will be briefly discussed. It is argued that correlations in quenched disorder -- needed to mimic cooperative Jahn-Teller effects -- are important to have colossal magnetoresistance in 3D. A related recently discussed metal-insulator transition induced by disorder in a one-orbital model with cooperative phonons is intuitively explained [1]. In addition, it is argued that colossal effects should be far more common than currently known, and they may appear in cuprate superconductors as well [2]. [1] J. Burgy et al., cond-mat/0308456; C. Sen, G. Alvarez, and E. Dagotto, preprint. [2] See also Adriana Moreo, invited talk, March APS 04; G. Alvarez, M. Mayr et al., preprint.

  4. Recombination Kinetics and Effects of Superacid Treatment in Sulfur- and Selenium-Based Transition Metal Dichalcogenides.

    PubMed

    Amani, Matin; Taheri, Peyman; Addou, Rafik; Ahn, Geun Ho; Kiriya, Daisuke; Lien, Der-Hsien; Ager, Joel W; Wallace, Robert M; Javey, Ali

    2016-04-13

    Optoelectronic devices based on two-dimensional (2D) materials have shown tremendous promise over the past few years; however, there are still numerous challenges that need to be overcome to enable their application in devices. These include improving their poor photoluminescence (PL) quantum yield (QY) as well as better understanding of exciton-based recombination kinetics. Recently, we developed a chemical treatment technique using an organic superacid, bis(trifluoromethane)sulfonimide (TFSI), which was shown to improve the quantum yield in MoS2 from less than 1% to over 95%. Here, we perform detailed steady-state and transient optical characterization on some of the most heavily studied direct bandgap 2D materials, specifically WS2, MoS2, WSe2, and MoSe2, over a large pump dynamic range to study the recombination mechanisms present in these materials. We then explore the effects of TFSI treatment on the PL QY and recombination kinetics for each case. Our results suggest that sulfur-based 2D materials are amenable to repair/passivation by TFSI, while the mechanism is thus far ineffective on selenium based systems. We also show that biexcitonic recombination is the dominant nonradiative pathway in these materials and that the kinetics for TFSI treated MoS2 and WS2 can be described using a simple two parameter model. PMID:26978038

  5. Piperazine pivoted transition metal dithiocarbamates

    NASA Astrophysics Data System (ADS)

    Khan, Sadaf; Nami, Shahab A. A.; Siddiqi, K. S.

    2008-03-01

    A quadridentate ligand disodium bis(2,2'-dithiopiperazinato-2,2'-diamino diethylamine) Na 2L 2 and its self assembled transition metal complexes of the type, M 2(L 2) 2 {M = Mn(II), Fe(II), Co(II), Ni(II), Cu(II), Zn(II), Cd(II) and Hg(II)} have been reported. The piperazine pivoted homodinuclear complexes have been characterized by a range of spectral, thermal, microanalytical and conductometric techniques. On the basis of IR and 1HNMR data a symmetrical bidentate coordination of the dithiocarbamato moiety has been observed in all the cases. The TGA profile of the ligand exhibits two stage thermolytic pattern although the complexes decompose in three steps, respectively. Metal sulfide is found to be the end product. The formation of homodinuclear complexes has been ascertained on the basis of FAB mass spectral data and a probable fragmentation pattern has been proposed. On the basis of UV-visible spectroscopic results and room temperature magnetic moment data a tetrahedral geometry has been proposed for all the complexes except for the Ni(II) and Cu(II) which are found to be square-planar.

  6. The dynamic behavior of thin-film ionic transition metal complex-based light-emitting electrochemical cells

    SciTech Connect

    Meier, Sebastian B. E-mail: wiebke.sarfert@siemens.com; Hartmann, David; Sarfert, Wiebke E-mail: wiebke.sarfert@siemens.com; Winnacker, Albrecht

    2014-09-14

    Light-emitting electrochemical cells (LECs) have received increasing attention during recent years due to their simple architecture, based on solely air-stabile materials, and ease of manufacture in ambient atmosphere, using solution-based technologies. The LEC's active layer offers semiconducting, luminescent as well as ionic functionality resulting in device physical processes fundamentally different as compared with organic light-emitting diodes. During operation, electrical double layers (EDLs) form at the electrode interfaces as a consequence of ion accumulation and electrochemical doping sets in leading to the in situ development of a light-emitting p-i-n junction. In this paper, we comment on the use of impedance spectroscopy in combination with complex nonlinear squares fitting to derive key information about the latter events in thin-film ionic transition metal complex-based light-emitting electrochemical cells based on the model compound bis-2-phenylpyridine 6-phenyl-2,2´-bipyridine iridium(III) hexafluoridophosphate ([Ir(ppy)₂(pbpy)][PF₆]). At operating voltages below the bandgap potential of the ionic complex used, we obtain the dielectric constant of the active layer, the conductivity of mobile ions, the transference numbers of electrons and ions, and the thickness of the EDLs, whereas the transient thickness of the p-i-n junction is determined at voltages above the bandgap potential. Most importantly, we find that charge transport is dominated by the ions when carrier injection from the electrodes is prohibited, that ion movement is limited by the presence of transverse internal interfaces and that the width of the intrinsic region constitutes almost 60% of the total active layer thickness in steady state at a low operating voltage.

  7. Assessing the density functional theory-based multireference configuration interaction (DFT/MRCI) method for transition metal complexes

    SciTech Connect

    Escudero, Daniel E-mail: thiel@kofo.mpg.de; Thiel, Walter E-mail: thiel@kofo.mpg.de

    2014-05-21

    We report an assessment of the performance of density functional theory-based multireference configuration interaction (DFT/MRCI) calculations for a set of 3d- and 4d-transition metal (TM) complexes. The DFT/MRCI results are compared to published reference data from reliable high-level multi-configurational ab initio studies. The assessment covers the relative energies of different ground-state minima of the highly correlated CrF{sub 6} complex, the singlet and triplet electronically excited states of seven typical TM complexes (MnO{sub 4}{sup −}, Cr(CO){sub 6}, [Fe(CN){sub 6}]{sup 4−}, four larger Fe and Ru complexes), and the corresponding electronic spectra (vertical excitation energies and oscillator strengths). It includes comparisons with results from different flavors of time-dependent DFT (TD-DFT) calculations using pure, hybrid, and long-range corrected functionals. The DFT/MRCI method is found to be superior to the tested TD-DFT approaches and is thus recommended for exploring the excited-state properties of TM complexes.

  8. Elution of Uranium and Transition Metals from Amidoxime-Based Polymer Adsorbents for Sequestering Uranium from Seawater

    SciTech Connect

    Pan, Horng-Bin; Kuo, Li-Jung; Wai, Chien M.; Miyamoto, Naomi; Joshi, Ruma; Wood, Jordana R.; Strivens, Jonathan E.; Janke, Christopher J.; Oyola, Yatsandra; Das, Sadananda; Mayes, Richard T.; Gill, Gary A.

    2015-11-30

    High-surface-area amidoxime and carboxylic acid grafted polymer adsorbents developed at Oak Ridge National Laboratory were tested for sequestering uranium in a flowing seawater flume system at the PNNL-Marine Sciences Laboratory. FTIR spectra indicate that a KOH conditioning process is necessary to remove the proton from the carboxylic acid and make the sorbent effective for sequestering uranium from seawater. The alkaline conditioning process also converts the amidoxime groups to carboxylate groups in the adsorbent. Both Na2CO3-H2O2 and hydrochloric acid elution methods can remove ~95% of the uranium sequestered by the adsorbent after 42 days of exposure in real seawater. The Na2CO3-H2O2 elution method is more selective for uranium than conventional acid elution. Iron and vanadium are the two major transition metals competing with uranium for adsorption to the amidoxime-based adsorbents in real seawater.

  9. Tunable Ultraviolet Photoresponse in Solution-Processed p-n Junction Photodiodes Based on Transition-Metal Oxides.

    PubMed

    Xie, Ting; Liu, Guannan; Wen, Baomei; Ha, Jong Y; Nguyen, Nhan V; Motayed, Abhishek; Debnath, Ratan

    2015-05-13

    Solution-processed p-n heterojunction photodiodes have been fabricated based on transition-metal oxides in which NiO and ternary Zn(1-x)Mg(x)O (x = 0-0.1) have been employed as p-type and n-type semiconductors, respectively. Composition-related structural, electrical, and optical properties are also investigated for all the films. It has been observed that the bandgap of Zn(1-x)Mg(x)O films can be tuned between 3.24 and 3.49 eV by increasing Mg content. The fabricated highly visible-blind p-n junction photodiodes show an excellent rectification ratio along with good photoresponse and quantum efficiency under ultraviolet (UV) illumination. With an applied reverse bias of 1 V and depending on the value of x, the maximum responsivity of the devices varies between 0.22 and 0.4 A/W and the detectivity varies between 0.17 × 10(12) and 2.2 × 10(12) cm (Hz)(1/2)/W. The photodetectors show an excellent UV-to-visible rejection ratio. Compositional nonuniformity has been observed locally in the alloyed films with x = 0.1, which is manifested in photoresponse and X-ray analysis data. This paper demonstrates simple solution-processed, low cost, band tunable photodiodes with excellent figures of merit operated under low bias. PMID:25898025

  10. Ferroelectric control of metal-insulator transition

    NASA Astrophysics Data System (ADS)

    He, Xu; Jin, Kui-juan; Ge, Chen; Ma, Zhong-shui; Yang, Guo-zhen

    2016-03-01

    We propose a method of controlling the metal-insulator transition of one perovskite material at its interface with another ferroelectric material based on first principle calculations. The operating principle is that the rotation of oxygen octahedra tuned by the ferroelectric polarization can modulate the superexchange interaction in this perovskite. We designed a tri-color superlattice of (BiFeO3)N/LaNiO3/LaTiO3, in which the BiFeO3 layers are ferroelectric, the LaNiO3 layer is the layer of which the electronic structure is to be tuned, and LaTiO3 layer is inserted to enhance the inversion asymmetry. By reversing the ferroelectric polarization in this structure, there is a metal-insulator transition of the LaNiO3 layer because of the changes of crystal field splitting of the Ni eg orbitals and the bandwidth of the Ni in-plane eg orbital. It is highly expected that a metal-transition can be realized by designing the structures at the interfaces for more materials.

  11. Induced anisotropy in FeCo-based nanocomposites: Early transition metal content dependence

    SciTech Connect

    Shen, S; DeGeorge, V; Ohodnicki, PR; Kernion, SJ; Keylin, V; Huth, JF; McHenry, ME

    2014-05-07

    Soft magnetic nanocomposites variants of FeCo-based (HTX002) alloys (Fe65Co35)(81+x)B12Nb4-xSi2Cu1, exhibiting high inductions (up to 1.9 T), low losses, and high temperature stability are studied for high frequency inductors and current sensors. For alloys with x 0, 1, 1.5, 2, and 3, we report field induced anisotropy, K-U, after annealing at temperatures of 340-450 degrees C for 1 h in a 2 T transverse magnetic field. The anisotropy field, H-K, measured by AC permeametry on toroidal cores, and by first order reversal curves on square sections of ribbon, decreases with annealing temperature and saturates at high annealing temperatures suggesting a nanostructure related anisotropy mechanism in which the amorphous phase exhibits a higher H-K than the crystalline phase. A high saturation induction nanocrystalline phase and high H-K amorphous phase were achieved by low temperature annealing resulting in a value of K-U exceeding 14 X 10(3) erg/cm(3), more than twice that reported previously for Fe-rich amorphous and nanocomposite alloys. (C) 2014 AIP Publishing LLC.

  12. High temperature thermoelectric properties of Zr and Hf based transition metal dichalcogenides: A first principles study.

    PubMed

    Yumnam, George; Pandey, Tribhuwan; Singh, Abhishek K

    2015-12-21

    We investigate the electronic and thermal transport properties of bulk MX2 compounds (M = Zr, Hf and X = S, Se) by first-principles calculations and semi-classical Boltzmann transport theory. The band structure shows the confinement of heavy and light bands along the out of plane and in-plane directions, respectively. This results in high electrical conductivity (σ) and large thermopower leading to a high power factor (S(2)σ) for moderate n-type doping. The phonon dispersion demonstrates low frequency flat acoustical modes, which results in low group velocities (vg). Consequently, lowering the lattice thermal conductivity (κlatt) below 2 W/m K. Low κlatt combined with high power factor results in ZT > 0.8 for all the bulk MX2 compounds at high temperature of 1200 K. In particular, the ZTmax of HfSe2 exceeds 1 at 1400 K. Our results show that Hf/Zr based dichalcogenides are very promising for high temperature thermoelectric application. PMID:26696067

  13. Induced anisotropy in FeCo-based nanocomposites: Early transition metal content dependence

    NASA Astrophysics Data System (ADS)

    Shen, S.; DeGeorge, V.; Ohodnicki, P. R.; Kernion, S. J.; Keylin, V.; Huth, J. F.; McHenry, M. E.

    2014-05-01

    Soft magnetic nanocomposites variants of FeCo-based (HTX002) alloys (Fe65Co35)81+xB12Nb4-xSi2Cu1, exhibiting high inductions (up to 1.9 T), low losses, and high temperature stability are studied for high frequency inductors and current sensors. For alloys with x = 0, 1, 1.5, 2, and 3, we report field induced anisotropy, KU, after annealing at temperatures of 340-450 °C for 1 h in a 2 T transverse magnetic field. The anisotropy field, HK, measured by AC permeametry on toroidal cores, and by first order reversal curves on square sections of ribbon, decreases with annealing temperature and saturates at high annealing temperatures suggesting a nanostructure related anisotropy mechanism in which the amorphous phase exhibits a higher HK than the crystalline phase. A high saturation induction nanocrystalline phase and high HK amorphous phase were achieved by low temperature annealing resulting in a value of KU exceeding 14 × 103 erg/cm3, more than twice that reported previously for Fe-rich amorphous and nanocomposite alloys.

  14. High temperature thermoelectric properties of Zr and Hf based transition metal dichalcogenides: A first principles study

    SciTech Connect

    Yumnam, George; Pandey, Tribhuwan; Singh, Abhishek K.

    2015-12-21

    We investigate the electronic and thermal transport properties of bulk MX{sub 2} compounds (M = Zr, Hf and X = S, Se) by first-principles calculations and semi-classical Boltzmann transport theory. The band structure shows the confinement of heavy and light bands along the out of plane and in-plane directions, respectively. This results in high electrical conductivity (σ) and large thermopower leading to a high power factor (S{sup 2}σ) for moderate n-type doping. The phonon dispersion demonstrates low frequency flat acoustical modes, which results in low group velocities (v{sub g}). Consequently, lowering the lattice thermal conductivity (κ{sub latt}) below 2 W/m K. Low κ{sub latt} combined with high power factor results in ZT > 0.8 for all the bulk MX{sub 2} compounds at high temperature of 1200 K. In particular, the ZT{sub max} of HfSe{sub 2} exceeds 1 at 1400 K. Our results show that Hf/Zr based dichalcogenides are very promising for high temperature thermoelectric application.

  15. Method for dry etching of transition metals

    DOEpatents

    Ashby, Carol I. H.; Baca, Albert G.; Esherick, Peter; Parmeter, John E.; Rieger, Dennis J.; Shul, Randy J.

    1998-01-01

    A method for dry etching of transition metals. The method for dry etching of a transition metal (or a transition metal alloy such as a silicide) on a substrate comprises providing at least one nitrogen- or phosphorous-containing .pi.-acceptor ligand in proximity to the transition metal, and etching the transition metal to form a volatile transition metal/.pi.-acceptor ligand complex. The dry etching may be performed in a plasma etching system such as a reactive ion etching (RIE) system, a downstream plasma etching system (i.e. a plasma afterglow), a chemically-assisted ion beam etching (CAIBE) system or the like. The dry etching may also be performed by generating the .pi.-acceptor ligands directly from a ligand source gas (e.g. nitrosyl ligands generated from nitric oxide), or from contact with energized particles such as photons, electrons, ions, atoms, or molecules. In some preferred embodiments of the present invention, an intermediary reactant species such as carbonyl or a halide ligand is used for an initial chemical reaction with the transition metal, with the intermediary reactant species being replaced at least in part by the .pi.-acceptor ligand for forming the volatile transition metal/.pi.-acceptor ligand complex.

  16. Method for dry etching of transition metals

    DOEpatents

    Ashby, C.I.H.; Baca, A.G.; Esherick, P.; Parmeter, J.E.; Rieger, D.J.; Shul, R.J.

    1998-09-29

    A method for dry etching of transition metals is disclosed. The method for dry etching of a transition metal (or a transition metal alloy such as a silicide) on a substrate comprises providing at least one nitrogen- or phosphorus-containing {pi}-acceptor ligand in proximity to the transition metal, and etching the transition metal to form a volatile transition metal/{pi}-acceptor ligand complex. The dry etching may be performed in a plasma etching system such as a reactive ion etching (RIE) system, a downstream plasma etching system (i.e. a plasma afterglow), a chemically-assisted ion beam etching (CAIBE) system or the like. The dry etching may also be performed by generating the {pi}-acceptor ligands directly from a ligand source gas (e.g. nitrosyl ligands generated from nitric oxide), or from contact with energized particles such as photons, electrons, ions, atoms, or molecules. In some preferred embodiments of the present invention, an intermediary reactant species such as carbonyl or a halide ligand is used for an initial chemical reaction with the transition metal, with the intermediary reactant species being replaced at least in part by the {pi}-acceptor ligand for forming the volatile transition metal/{pi}-acceptor ligand complex.

  17. Thermodynamic Hydricity of Transition Metal Hydrides.

    PubMed

    Wiedner, Eric S; Chambers, Matthew B; Pitman, Catherine L; Bullock, R Morris; Miller, Alexander J M; Appel, Aaron M

    2016-08-10

    Transition metal hydrides play a critical role in stoichiometric and catalytic transformations. Knowledge of free energies for cleaving metal hydride bonds enables the prediction of chemical reactivity, such as for the bond-forming and bond-breaking events that occur in a catalytic reaction. Thermodynamic hydricity is the free energy required to cleave an M-H bond to generate a hydride ion (H(-)). Three primary methods have been developed for hydricity determination: the hydride transfer method establishes hydride transfer equilibrium with a hydride donor/acceptor pair of known hydricity, the H2 heterolysis method involves measuring the equilibrium of heterolytic cleavage of H2 in the presence of a base, and the potential-pKa method considers stepwise transfer of a proton and two electrons to give a net hydride transfer. Using these methods, over 100 thermodynamic hydricity values for transition metal hydrides have been determined in acetonitrile or water. In acetonitrile, the hydricity of metal hydrides spans a range of more than 50 kcal/mol. Methods for using hydricity values to predict chemical reactivity are also discussed, including organic transformations, the reduction of CO2, and the production and oxidation of hydrogen. PMID:27483171

  18. Synthesis of arsenic transition metal sulfides and metal arsenides

    SciTech Connect

    Singhal, G.H.; Brown, L.D.; Ryan, D.F.

    1993-12-31

    One of the chief problems in upgrading shale oil is the presence of inherent arsenic which is known to poison downstream catalysts. Highly dispersed transition metal sulfides formed in situ from the decomposition of dithiocarbamate (DTC) complexes of transition metals show excellent potential as dearsenation agents. The authors have studied the reaction of these sulfides with various arsenic compositions and characterized the metal arsenides and arsenic metal sulfides formed as well as the ease of their formation. Thus, the reaction of bis(butyldithiocarbamato)Ni, (NiBuDTC) with model compounds was very facile and gave NiAs, NiAsS, and NiAs2=xSx. In general the effectiveness of the sulfides for dearsenation followed the sequence Ni>Mo{much_gt}Co, while iron sulfides were totally ineffective. Based upon these results, tests were run in autoclaves (as well as a fixed-bed flow-through unit) with NiBuDTC and shale oil having 73 ppm inherent As. Under optimum conditions, dearsenation down to les than 1 ppm was obtained.

  19. Superconducting Metallic Glass Transition-Edge-Sensors

    NASA Technical Reports Server (NTRS)

    Hays, Charles C. (Inventor)

    2013-01-01

    A superconducting metallic glass transition-edge sensor (MGTES) and a method for fabricating the MGTES are provided. A single-layer superconducting amorphous metal alloy is deposited on a substrate. The single-layer superconducting amorphous metal alloy is an absorber for the MGTES and is electrically connected to a circuit configured for readout and biasing to sense electromagnetic radiation.

  20. WASP-36b: A NEW TRANSITING PLANET AROUND A METAL-POOR G-DWARF, AND AN INVESTIGATION INTO ANALYSES BASED ON A SINGLE TRANSIT LIGHT CURVE

    SciTech Connect

    Smith, A. M. S.; Anderson, D. R.; Hellier, C.; Maxted, P. F. L.; Smalley, B.; Southworth, J.; Collier Cameron, A.; Gillon, M.; Jehin, E.; Lendl, M.; Queloz, D.; Triaud, A. H. M. J.; Pepe, F.; Segransan, D.; Udry, S.; West, R. G.; Barros, S. C. C.; Pollacco, D.; Street, R. A.

    2012-04-15

    We report the discovery, from WASP and CORALIE, of a transiting exoplanet in a 1.54 day orbit. The host star, WASP-36, is a magnitude V = 12.7, metal-poor G2 dwarf (T{sub eff} = 5959 {+-} 134 K), with [Fe/H] =-0.26 {+-} 0.10. We determine the planet to have mass and radius, respectively, 2.30 {+-} 0.07 and 1.28 {+-} 0.03 times that of Jupiter. We have eight partial or complete transit light curves, from four different observatories, which allow us to investigate the potential effects on the fitted system parameters of using only a single light curve. We find that the solutions obtained by analyzing each of these light curves independently are consistent with our global fit to all the data, despite the apparent presence of correlated noise in at least two of the light curves.

  1. DNA-based biosensor for comparative study of catalytic effect of transition metals on autoxidation of sulfite.

    PubMed

    Ensafi, Ali A; Heydari-Bafrooei, Esmaeil; Rezaei, Behzad

    2013-01-15

    The transition metal-catalyzed oxidation of sulfur(IV) oxides has been known for more than 100 years. However, to the best of the authors' knowledge, no electrochemical quantitative study has yet been carried out to determine its nature. In view of the transition metal catalyzed oxidation of sulfur(IV) oxides, a series of radicals are involved in the overall reaction process whereby the sulfite, in the presence of transition metals, may cause damages to DNA through the generation of these highly reactive species. In the present work, {MWCNTs-PDDA/DNA}(2) layer-by-layer (LBL) films were prepared to detect DNA damage induced by radicals generated from sulfite autoxidation using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The change in the peak potential separation (ΔE(p)) and charge transfer resistance (R(p)) after incubation of the DNA biosensor in the damaging solution for a certain time was used as indicators of DNA damage. It was found that sulfite in the presence of Co(II), Cu(II), Cr(VI), Fe(III), and Mn(II) caused damage to DNA while neither sulfite alone nor metal ions alone did have the same effect. The results suggest that sulfite is rapidly autoxidized in the presence of Co(II), Cu(II), Cr(VI), Fe(III), and Mn(II), producing radicals that cause the DNA damage. These radicals can be ranked in a descending order of their ability to induce DNA damage with sulfite as follows: Fe(III) > Co(II) > Cu(II) > Cr(VI) > Mn(II). The DNA damage induced by sulfite plus Co(II), Cr(VI), and Fe(III) was inhibited by primary alcohols, but they were not when superoxide dismutase (SOD) and tert-butyl alcohol were used. Comparison of methods used to determine the minimum concentration of a transition metal for sulfite induced DNA damage revealed that electrochemical impedance spectroscopy and cyclic voltammetry outperformed the quantitative comparison of different reagents. PMID:23244055

  2. Synchronization of pairwise-coupled, identical, relaxation oscillators based on metal-insulator phase transition devices: A model study

    NASA Astrophysics Data System (ADS)

    Parihar, Abhinav; Shukla, Nikhil; Datta, Suman; Raychowdhury, Arijit

    2015-02-01

    Computing with networks of synchronous oscillators has attracted wide-spread attention as novel materials and device topologies have enabled realization of compact, scalable and low-power coupled oscillatory systems. Of particular interest are compact and low-power relaxation oscillators that have been recently demonstrated using MIT (metal-insulator-transition) devices using properties of correlated oxides. Further the computational capability of pairwise coupled relaxation oscillators has also been shown to outperform traditional Boolean digital logic circuits. This paper presents an analysis of the dynamics and synchronization of a system of two such identical coupled relaxation oscillators implemented with MIT devices. We focus on two implementations of the oscillator: (a) a D-D configuration where complementary MIT devices (D) are connected in series to provide oscillations and (b) a D-R configuration where it is composed of a resistor (R) in series with a voltage-triggered state changing MIT device (D). The MIT device acts like a hysteresis resistor with different resistances in the two different states. The synchronization dynamics of such a system has been analyzed with purely charge based coupling using a resistive (RC) and a capacitive (CC) element in parallel. It is shown that in a D-D configuration symmetric, identical and capacitively coupled relaxation oscillator system synchronizes to an anti-phase locking state, whereas when coupled resistively the system locks in phase. Further, we demonstrate that for certain range of values of RC and CC, a bistable system is possible which can have potential applications in associative computing. In D-R configuration, we demonstrate the existence of rich dynamics including non-monotonic flows and complex phase relationship governed by the ratios of the coupling impedance. Finally, the developed theoretical formulations have been shown to explain experimentally measured waveforms of such pairwise coupled

  3. Synthesis, thermal and spectral studies of first-row transition metal complexes with girard P reagent-based ligand

    NASA Astrophysics Data System (ADS)

    El-Ayaan, Usama; Kenawy, I. M.; El-Reash, Y. G. Abu

    2007-10-01

    A new series of first-row transition metal complexes with 1-acetylpyridinium chloride-4-benzoyl thiosemicarbazide (H 2GPBzIT) have been prepared and characterized by elemental analysis, spectroscopic and magnetic measurements. The proton-ligand ionization constants were determined potentiometrically using Irving-Rossotti technique. The stability constants of complexes were also calculated and were found in agreement with the seq uence of stability constants of Irving and Williams. Thermal stability and degradation kinetics have been measured using thermogravimetric analyzer. Kinetic parameters were obtained for each stage of thermal degradation of complexes using Coats-Redfern method.

  4. Raman spectroscopy of transition metal dichalcogenides.

    PubMed

    Saito, R; Tatsumi, Y; Huang, S; Ling, X; Dresselhaus, M S

    2016-09-01

    Raman spectroscopy of transition metal dichalcogenides (TMDs) is reviewed based on our recent theoretical and experimental works. First, we discuss the semi-classical and quantum mechanical description for the polarization dependence of Raman spectra of TMDs in which the optical dipole transition matrix elements as a function of laser excitation energy are important for understanding the polarization dependence of the Raman intensity and Raman tensor. Overviewing the symmetry of TMDs, we discuss the dependence of the Raman spectra of TMDs on layer thickness, polarization, laser energy and the structural phase. Furthermore, we discuss the Raman spectra of twisted bilayer and heterostructures of TMDs. Finally, we give our perspectives on the Raman spectroscopy of TMDs. PMID:27388703

  5. Raman spectroscopy of transition metal dichalcogenides

    NASA Astrophysics Data System (ADS)

    Saito, R.; Tatsumi, Y.; Huang, S.; Ling, X.; Dresselhaus, M. S.

    2016-09-01

    Raman spectroscopy of transition metal dichalcogenides (TMDs) is reviewed based on our recent theoretical and experimental works. First, we discuss the semi-classical and quantum mechanical description for the polarization dependence of Raman spectra of TMDs in which the optical dipole transition matrix elements as a function of laser excitation energy are important for understanding the polarization dependence of the Raman intensity and Raman tensor. Overviewing the symmetry of TMDs, we discuss the dependence of the Raman spectra of TMDs on layer thickness, polarization, laser energy and the structural phase. Furthermore, we discuss the Raman spectra of twisted bilayer and heterostructures of TMDs. Finally, we give our perspectives on the Raman spectroscopy of TMDs.

  6. Multifunctional Ligands in Transition Metal Catalysis

    SciTech Connect

    Crabtree, Robert H

    2011-01-01

    Sophisticated ligands are now being designed that do far more than just fulfil their traditional spectator roles by binding to the metal and providing a sterically-defined binding pocket for the substrate in homogeneous transition metal catalysis. This Focus review emphasizes selected cases in which ligands carry additional functional groups that change the properties of the ligand as a result of an external stimulus or undergo catalytically-relevant ligand-based reactivity. These include proton responsive ligands capable of gaining or losing one or more protons, ligands having a hydrogen bonding function, electroresponsive ligands capable of gaining or losing one or more electrons, and photoresponsive ligands capable of undergoing a useful change of properties upon irradiation. Molecular recognition ligands and proton coupled electron transfer (PCET) are briefly discussed.

  7. New pathways for organic synthesis. Practical applications of transition metals

    SciTech Connect

    Colquhoun, H.M.; Holton, J.; Thompson, D.J.; Twigg, M.V.

    1984-01-01

    This book contains a considerable number of transition-metal-based procedures that have genuine applications in synthesis, and which are arranged according to the nature of the organic product or synthetic transformation being carried out. The objective is to provide those engaged in the preparation of pharmaceuticals, natural products, herbicides, dyestuffs, and other organic chemicals with a practical guide to the application of transition metals in organic synthesis. Topics considered include the formation of carbon-carbon bonds, the formation of carbocyclic compounds, the formation of heterocyclic compounds, the isomerization of alkenes, the direct introduction and removal of carbonyl groups, reduction, oxidation, and preparing and handling transition metal catalysts.

  8. Base-promoted synthesis of coumarins from salicylaldehydes and aryl-substituted 1,1-dibromo-1-alkenes under transition-metal-free conditions.

    PubMed

    Liu, Jianming; Zhang, Xin; Shi, Lijun; Liu, Muwen; Yue, Yuanyuan; Li, Fuwei; Zhuo, Kelei

    2014-09-01

    Facile synthesis of coumarin via the tandem reaction of salicylaldehyde with aryl-substituted 1,1-dibromo-1-alkene was developed. This new protocol proceeds smoothly under mild and transition-metal-free conditions, it allows rapid access to coumarins containing various heteroatoms that are more difficult to prepare by traditional methods. Based on the isolated intermediate of 4-(diethylamino)-3-phenylchroman-2-one and detailed mechanistic studies, a credible tandem pathway was proposed. PMID:25027244

  9. Electronic doping of transition metal oxide perovskites

    NASA Astrophysics Data System (ADS)

    Cammarata, Antonio; Rondinelli, James M.

    2016-05-01

    CaFeO3 is a prototypical negative charge transfer oxide that undergoes electronic metal-insulator transition concomitant with a dilation and contraction of nearly rigid octahedra. Altering the charge neutrality of the bulk system destroys the electronic transition, while the structure is significantly modified at high charge content. Using density functional theory simulations, we predict an alternative avenue to modulate the structure and the electronic transition in CaFeO3. Charge distribution can be modulated using strain-rotation coupling and thin film engineering strategies, proposing themselves as a promising avenue for fine tuning electronic features in transition metal-oxide perovskites.

  10. Ultrafast photophysics of transition metal complexes.

    PubMed

    Chergui, Majed

    2015-03-17

    The properties of transition metal complexes are interesting not only for their potential applications in solar energy conversion, OLEDs, molecular electronics, biology, photochemistry, etc. but also for their fascinating photophysical properties that call for a rethinking of fundamental concepts. With the advent of ultrafast spectroscopy over 25 years ago and, more particularly, with improvements in the past 10-15 years, a new area of study was opened that has led to insightful observations of the intramolecular relaxation processes such as internal conversion (IC), intersystem crossing (ISC), and intramolecular vibrational redistribution (IVR). Indeed, ultrafast optical spectroscopic tools, such as fluorescence up-conversion, show that in many cases, intramolecular relaxation processes can be extremely fast and even shorter than time scales of vibrations. In addition, more and more examples are appearing showing that ultrafast ISC rates do not scale with the magnitude of the metal spin-orbit coupling constant, that is, that there is no heavy-atom effect on ultrafast time scales. It appears that the structural dynamics of the system and the density of states play a crucial role therein. While optical spectroscopy delivers an insightful picture of electronic relaxation processes involving valence orbitals, the photophysics of metal complexes involves excitations that may be centered on the metal (called metal-centered or MC) or the ligand (called ligand-centered or LC) or involve a transition from one to the other or vice versa (called MLCT or LMCT). These excitations call for an element-specific probe of the photophysics, which is achieved by X-ray absorption spectroscopy. In this case, transitions from core orbitals to valence orbitals or higher allow probing the electronic structure changes induced by the optical excitation of the valence orbitals, while also delivering information about the geometrical rearrangement of the neighbor atoms around the atom of

  11. Transition Metal Nitrides: A First Principles Study

    NASA Astrophysics Data System (ADS)

    Pathak, Ashish; Singh, A. K.

    2016-04-01

    The present work describes the structural stability and electronic and mechanical properties of transition metal nitrides (TmNs: B1 cubic structure (cF8, Fm ‾ overline 3 m)) using first principles density functional theory (DFT) within generalized gradient approximation (GGA). The lattice constant of TmNs increases with increasing the atomic radii of the transition metals. Stability of the TmNs decreases from IVB to VIB groups due to increase in formation energy/atom. The bonding characteristics of these nitrides have been explained based on electronic density of states and charge density. All the TmNs satisfy Born stability criteria in terms of elastic constants except CrN and MoN that do not exist in equilibrium binary phase diagrams. The groups IVB and V-VIB nitrides are associated with brittle and ductile behaviour based on G/B ratios, respectively. The estimated melting temperatures of these nitrides exhibit reasonably good agreement with calculated with B than those of the C11 for all nitrides.

  12. Tunable magnetocaloric effect in transition metal alloys.

    PubMed

    Belyea, Dustin D; Lucas, M S; Michel, E; Horwath, J; Miller, Casey W

    2015-01-01

    The unpredictability of geopolitical tensions and resulting supply chain and pricing instabilities make it imperative to explore rare earth free magnetic materials. As such, we have investigated fully transition metal based "high entropy alloys" in the context of the magnetocaloric effect. We find the NiFeCoCrPdx family exhibits a second order magnetic phase transition whose critical temperature is tunable from 100 K to well above room temperature. The system notably displays changes in the functionality of the magnetic entropy change depending on x, which leads to nearly 40% enhancement of the refrigerant capacity. A detailed statistical analysis of the universal scaling behavior provides direct evidence that heat treatment and Pd additions reduce the distribution of exchange energies in the system, leading to a more magnetically homogeneous alloy. The general implications of this work are that the parent NiFeCoCr compound can be tuned dramatically with FCC metal additives. Together with their relatively lower cost, their superior mechanical properties that aid manufacturability and their relative chemical inertness that aids product longevity, NiFeCoCr-based materials could ultimately lead to commercially viable magnetic refrigerants. PMID:26507636

  13. Tunable magnetocaloric effect in transition metal alloys

    PubMed Central

    Belyea, Dustin D.; Lucas, M. S.; Michel, E.; Horwath, J.; Miller, Casey W.

    2015-01-01

    The unpredictability of geopolitical tensions and resulting supply chain and pricing instabilities make it imperative to explore rare earth free magnetic materials. As such, we have investigated fully transition metal based “high entropy alloys” in the context of the magnetocaloric effect. We find the NiFeCoCrPdx family exhibits a second order magnetic phase transition whose critical temperature is tunable from 100 K to well above room temperature. The system notably displays changes in the functionality of the magnetic entropy change depending on x, which leads to nearly 40% enhancement of the refrigerant capacity. A detailed statistical analysis of the universal scaling behavior provides direct evidence that heat treatment and Pd additions reduce the distribution of exchange energies in the system, leading to a more magnetically homogeneous alloy. The general implications of this work are that the parent NiFeCoCr compound can be tuned dramatically with FCC metal additives. Together with their relatively lower cost, their superior mechanical properties that aid manufacturability and their relative chemical inertness that aids product longevity, NiFeCoCr-based materials could ultimately lead to commercially viable magnetic refrigerants. PMID:26507636

  14. Tunable magnetocaloric effect in transition metal alloys

    NASA Astrophysics Data System (ADS)

    Belyea, Dustin D.; Lucas, M. S.; Michel, E.; Horwath, J.; Miller, Casey W.

    2015-10-01

    The unpredictability of geopolitical tensions and resulting supply chain and pricing instabilities make it imperative to explore rare earth free magnetic materials. As such, we have investigated fully transition metal based “high entropy alloys” in the context of the magnetocaloric effect. We find the NiFeCoCrPdx family exhibits a second order magnetic phase transition whose critical temperature is tunable from 100 K to well above room temperature. The system notably displays changes in the functionality of the magnetic entropy change depending on x, which leads to nearly 40% enhancement of the refrigerant capacity. A detailed statistical analysis of the universal scaling behavior provides direct evidence that heat treatment and Pd additions reduce the distribution of exchange energies in the system, leading to a more magnetically homogeneous alloy. The general implications of this work are that the parent NiFeCoCr compound can be tuned dramatically with FCC metal additives. Together with their relatively lower cost, their superior mechanical properties that aid manufacturability and their relative chemical inertness that aids product longevity, NiFeCoCr-based materials could ultimately lead to commercially viable magnetic refrigerants.

  15. Synthesis, Spectral Characterization, and Biological Evaluation of Transition Metal Complexes of Bidentate N, O Donor Schiff Bases

    PubMed Central

    Sumrra, Sajjad Hussain; Ambreen, Sabahat; Imran, Muhammad; Danish, Muhammad; Rehmani, Fouzia Sultana

    2014-01-01

    New series of three bidentate N, O donor type Schiff bases (L1)–(L3) were prepared by using ethylene-1,2-diamine with 5-methyl furfural, 2-anisaldehyde, and 2-hydroxybenzaldehyde in an equimolar ratio. These ligands were further complexed with Co(II), Cu(II), Ni(II), and Zn(II) metals to produce their new metal complexes having an octahedral geometry. These compounds were characterized on the basis of their physical, spectral, and analytical data. Elemental analysis and spectral data of the uncomplexed ligands and their metal(II) complexes were found to be in good agreement with their structures, indicating high purity of all the compounds. All ligands and their metal complexes were screened for antimicrobial activity. The results of antimicrobial activity indicated that metal complexes have significantly higher activity than corresponding ligands. This higher activity might be due to chelation process which reduces the polarity of metal ion by coordinating with ligands. PMID:25147493

  16. Thermomechanical properties of 3d transition metals

    SciTech Connect

    Karaoglu, B.; Rahman, S.M.M. . Dept. of Physics)

    1994-05-15

    The authors have investigated the density variation of the Einstein temperatures and elastic constants of the 3d transition metals. In this respect they have employed the transition metal (TM) pair potentials involving the sp contribution with an appropriate exchange and correlation function, the d-band broadening contribution and the d-band hybridization term. These calculations are aimed at testing the TM pair potentials in generating the quasilocal and local thermomechanical properties.

  17. Bi-phase transition diagrams of metallic thin multilayers

    SciTech Connect

    Li, J.C.; Liu, W.; Jiang, Q. . E-mail: jiangq@jlu.edu.cn

    2005-02-01

    Phase transitions of metallic multilayers induced by differences in interface energy are considered thermodynamically, based on a thermodynamic model for interface energy and the Goldschmidt premise for lattice contraction. Bi-phase transition diagrams of Co/Cr, Zr/Nb, Ti/Nb and Ti/Al multilayers are constructed, which are in agreement with experimental results.

  18. Four Hybrid Materials Based on Preyssler P5W30 Polyoxometalate and First-Row Transition-Metal Complex.

    PubMed

    Hu, Tuo-Ping; Zhao, Ya-Qin; Jagličić, Zvonko; Yu, Kai; Wang, Xing-Po; Sun, Di

    2015-08-01

    Four Preyssler P5W30 based inorganic-organic hybrids, formulated as {[Cu12(pbtz)2(Hpbtz)2(OH)4(H2O)16][Na(H2O)P5W30O110]}·16H2O (1; H2pbtz = 5'-(pyridin-2-yl)-1H,2'H-3,3'-bi(1,2,4-triazole)), {[Cu10(ttbz)2(Httbz)4(OH)6(H2O)8][K(H2O)H2P5W30O110]}·30H2O (2; Httbz = 1-(tetrazo-5-yl)-4-(triazo-1-yl)benzene), {[Ni6(bpz)6(H2O)16][Na(H2O)H2P5W30O110]}·36H2O (3; bpz = 3,3',5,5'-tetramethyl-4,4-bipyrazole), {[Co4(bpz)6(H2O)9][K(H2O)H6P5W30O110]}·46H2O (4), have been isolated and structurally identified via microanalysis, thermogravimetry (TG), infrared (IR) spectroscopy, and X-ray single-crystal diffraction. Compound 1 exhibits a 3D binodal (3,6)-connected ant framework composed of dodeca-supported P5W30 polyoxometalate (POM) clusters and discrete [Cu6(pbtz)(Hpbtz)(OH)2(H2O)8] subunits. Compound 2 is a pillared-layer 3D network constructed from [Cu5(ttbz)(Httbz)2(OH)3(H2O)4] sheets pillared by individual P5W30 clusters. Compound 3 contains octa-supporting P5W30 POM clusters and novel [Ni6(bpz)6] crown-like metallamacrocycles, which construct a (4,4)-connected pts network. Compound 4 displays a complicated 3D (5,5)-connected {4(5)·6(4)·8}{4(5)·6(5)} network built by pentasupporting P5W30 POM clusters and discrete [Co4(bpz)6(H2O)9] subunits. In 1-4, the unified features are the Preyssler-type [P5W30O110] POM as the fundamental building block, which supports the transition-metal compounds with different modes to give the resultant diverse networks. The magnetism studies indicated antiferromagnetically coupled systems for the hexa- and pentanuclear Cu(II) units in 1 and 2, respectively. The electrochemical properties demonstrate that all compounds have electrocatalytic abilities toward the reduction of hydrogen peroxide. Furthermore, the catalytic activities of 1 in the cyanosilylation of aldehydes reaction have been investigated. PMID:26196681

  19. Defect-Tolerant Monolayer Transition Metal Dichalcogenides.

    PubMed

    Pandey, Mohnish; Rasmussen, Filip A; Kuhar, Korina; Olsen, Thomas; Jacobsen, Karsten W; Thygesen, Kristian S

    2016-04-13

    Localized electronic states formed inside the band gap of a semiconductor due to crystal defects can be detrimental to the material's optoelectronic properties. Semiconductors with a lower tendency to form defect induced deep gap states are termed defect-tolerant. Here we provide a systematic first-principles investigation of defect tolerance in 29 monolayer transition metal dichalcogenides (TMDs) of interest for nanoscale optoelectronics. We find that the TMDs based on group VI and X metals form deep gap states upon creation of a chalcogen (S, Se, Te) vacancy, while the TMDs based on group IV metals form only shallow defect levels and are thus predicted to be defect-tolerant. Interestingly, all the defect sensitive TMDs have valence and conduction bands with a very similar orbital composition. This indicates a bonding/antibonding nature of the gap, which in turn suggests that dangling bonds will fall inside the gap. These ideas are made quantitative by introducing a descriptor that measures the degree of similarity of the conduction and valence band manifolds. Finally, the study is generalized to nonpolar nanoribbons of the TMDs where we find that only the defect sensitive materials form edge states within the band gap. PMID:27027786

  20. Protein-Transition Metal Ion Networks

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Proteins obtained from agricultural sources were blended with divalent metal ions. Feather keratin, egg albumin, and wheat gluten showed increases of 2-3 times in modulus with addition of divalent transition metal ions Cu2+ and Zn2+. Increasing concentrations of ions resulted in increased stiffnes...

  1. Methyl Complexes of the Transition Metals.

    PubMed

    Campos, Jesús; López-Serrano, Joaquín; Peloso, Riccardo; Carmona, Ernesto

    2016-05-01

    Organometallic chemistry can be considered as a wide area of knowledge that combines concepts of classic organic chemistry, that is, based essentially on carbon, with molecular inorganic chemistry, especially with coordination compounds. Transition-metal methyl complexes probably represent the simplest and most fundamental way to view how these two major areas of chemistry combine and merge into novel species with intriguing features in terms of reactivity, structure, and bonding. Citing more than 500 bibliographic references, this review aims to offer a concise view of recent advances in the field of transition-metal complexes containing M-CH3 fragments. Taking into account the impressive amount of data that are continuously provided by organometallic chemists in this area, this review is mainly focused on results of the last five years. After a panoramic overview on M-CH3 compounds of Groups 3 to 11, which includes the most recent landmark findings in this area, two further sections are dedicated to methyl-bridged complexes and reactivity. PMID:26991740

  2. Synthesis, characterization and biological approach of metal chelates of some first row transition metal ions with halogenated bidentate coumarin Schiff bases containing N and O donor atoms.

    PubMed

    Prabhakara, Chetan T; Patil, Sangamesh A; Toragalmath, Shivakumar S; Kinnal, Shivashankar M; Badami, Prema S

    2016-04-01

    The impregnation of halogen atoms in a molecule is an emerging trend in pharmaceutical chemistry. The presence of halogens (Cl, Br, I and F) increases the lipophilic nature of molecule and improves the penetration of lipid membrane. The presence of electronegative halogen atoms increases the bio- activity of core moiety. In the present study, Co(II), Ni(II) and Cu(II) complexes are synthesised using Schiff bases (HL(I) and HL(II)), derived from 8-formyl-7-hydroxy-4-methylcoumarin/3-chloro-8-formyl-7-hydroxy-4-methylcoumarin with 2,4-difluoroaniline/o-toluidine respectively. The synthesized compounds were characterized by spectral (IR, NMR, UV-visible, Mass, ESI-MS, ESR), thermal, fluorescence and molar conductivity studies. All the synthesized metal complexes are completely soluble in DMF and DMSO. The non-electrolytic nature of the metal complexes was confirmed by molar conductance studies. Elemental analysis study suggest [ML2(H2O)2] stoichiometry, here M=Co(II), Ni(II) and Cu(II), L=deprotonated ligand. The obtained IR data supports the binding of metal ion to Schiff base. Thermal study suggests the presence of coordinated water molecules. Electronic spectral results reveal six coordinated geometry for the synthesized metal complexes. The Schiff bases and their metal complexes were evaluated for antibacterial (Pseudomonas aureginosa and Proteus mirabilis), antifungal (Aspergillus niger and Rhizopus oryzae), anthelmintic (Pheretima posthuma) and DNA cleavage (Calf Thymus DNA) activities. PMID:26874303

  3. Synthesis, characterization and antibacterial activity of a Schiff base derived from cephalexin and sulphathiazole and its transition metal complexes

    NASA Astrophysics Data System (ADS)

    Anacona, J. R.; Rodriguez, Juan Luis; Camus, Juan

    2014-08-01

    Metal(II) coordination compounds of a cephalexin Schiff base (HL) derived from the condensation of cephalexin antibiotic with sulphathiazole were synthesized. The Schiff base ligand, mononuclear [ML(OAc)(H2O)2] (M(II) = Mn, Co, Ni, Zn) complexes and magnetically diluted trinuclear copper(II) complex [Cu3L(OH)5] were characterized by several techniques, including elemental and thermal analysis, molar conductance and magnetic susceptibility measurements, electronic, FT-IR, EPR and 1H NMR spectral studies. The analytical and molar conductance values indicated that the acetate ions coordinate to the metal ions. The Schiff base ligand HL behaves as a monoanionic tridentate NNO and tetradentate NNOO chelating agent in the mono and trinuclear complexes respectively.

  4. Synthesis, thermal and spectral studies of first-row transition metal complexes with Girard-T reagent-based ligand

    NASA Astrophysics Data System (ADS)

    El-Ayaan, Usama; Kenawy, I. M.; Abu El-Reash, Y. G.

    2007-12-01

    The complexing behaviour of 1-acetyltrimethyl ammonium chloride-4-benzoyl thiosemicarbazide (H 2GTBzIT) towards the following first-row transition metal ions namely, Cr(III), Mn(II), Co(II), Ni(II), Cu(II) and Zn(II) have been examined by elemental analysis, magnetic measurements, electronic, IR and 1H NMR. The proton-ligand ionization constants were determined potentiometrically using Irving-Rossotti technique. The stability constants of complexes were also calculated and were found in agreement with the sequence of stability constants of Irving and Williams. Thermal properties and decomposition kinetics of all complexes are investigated. The interpretation, mathematical analysis and evaluation of kinetic parameters ( E, A, Δ H, Δ S and Δ G) of all thermal decomposition stages have been evaluated using Coats-Redfern and Horowitz-Metzger equations.

  5. “Nok”. A Phytosterol-Based Amphiphile Enabling Transition Metal-Catalyzed Couplings in Water at Room Temperature

    PubMed Central

    Klumphu, Piyatida

    2014-01-01

    The third generation designer amphiphile/surfactant, “Nok” (i.e., SPGS-550-M; β-sitosteryl polyoxoethanylsuccinate), soon to be commercially available from Aldrich, can be prepared in two steps using an abundant plant feedstock, β-sitosterol, together with succinic anhydride and PEG-550-M. Upon dissolution in water it forms nanomicelles that serve as nanoreactors, which can be characterized by both cryo-TEM and dynamic light scattering analyses. Several transition metal-catalyzed reactions have been run under micellar conditions to evaluate this surfactant relative to results obtained in nanoparticles composed of TPGS-750-M (i.e., a second generation surfactant). It is shown that Nok usually affords yields that are, in general, as good or better than those typically obtained with TPGS-750-M, and yet is far less costly. PMID:24447127

  6. Transition metal contacts to graphene

    SciTech Connect

    Politou, Maria De Gendt, Stefan; Heyns, Marc; Asselberghs, Inge; Radu, Iuliana; Conard, Thierry; Richard, Olivier; Martens, Koen; Huyghebaert, Cedric; Tokei, Zsolt; Lee, Chang Seung; Sayan, Safak

    2015-10-12

    Achieving low resistance contacts to graphene is a common concern for graphene device performance and hybrid graphene/metal interconnects. In this work, we have used the circular Transfer Length Method (cTLM) to electrically characterize Ag, Au, Ni, Ti, and Pd as contact metals to graphene. The consistency of the obtained results was verified with the characterization of up to 72 cTLM structures per metal. Within our study, the noble metals Au, Ag and Pd, which form a weaker bond with graphene, are shown to result in lower contact resistance (Rc) values compared to the more reactive Ni and Ti. X-ray Photo Electron Spectroscopy and Transmission Electron Microscopy characterization for the latter have shown the formation of Ti and Ni carbides. Graphene/Pd contacts show a distinct intermediate behavior. The weak carbide formation signature and the low Rc values measured agree with theoretical predictions of an intermediate state of weak chemisorption of Pd on graphene.

  7. Transition metal catalysis in confined spaces.

    PubMed

    Leenders, Stefan H A M; Gramage-Doria, Rafael; de Bruin, Bas; Reek, Joost N H

    2015-01-21

    Transition metal catalysis plays an important role in both industry and in academia where selectivity, activity and stability are crucial parameters to control. Next to changing the structure of the ligand, introducing a confined space as a second coordination sphere around a metal catalyst has recently been shown to be a viable method to induce new selectivity and activity in transition metal catalysis. In this review we focus on supramolecular strategies to encapsulate transition metal complexes with the aim of controlling the selectivity via the second coordination sphere. As we will discuss, catalyst confinement can result in selective processes that are impossible or difficult to achieve by traditional methods. We will describe the template-ligand approach as well as the host-guest approach to arrive at such supramolecular systems and discuss how the performance of the catalyst is enhanced by confining it in a molecular container. PMID:25340992

  8. Method of boronizing transition-metal surfaces

    SciTech Connect

    Koyama, K.; Shimotake, H.

    1981-08-28

    A method is presented for preparing a boride layer on a transition metal substrate for use in corrosive environments or as a harden surface in machine applications. This method is particularly useful in treating current collectors for use within a high temperature and corrosive electrochemical cell environment. A melt of a alkali metal boride tetrafluoride salt including such as KF to lower its melting point is prepared including a dissolved boron containing material, for instance NiB, MnB/sub 2/, or CrB/sub 2/. A transition metal to be coated is immersed in the melt at a temperature of no more than 700/sup 0/C and a surface boride layer of that transition metal is formed within a period of about 24 hours on the substrate surface.

  9. Method of boronizing transition metal surfaces

    DOEpatents

    Koyama, Koichiro; Shimotake, Hiroshi

    1983-01-01

    A method is presented for preparing a boride layer on a transition metal substrate for use in corrosive environments or as a harden surface in machine applications. This method is particularly useful in treating current collectors for use within a high temperature and corrosive electrochemical cell environment. A melt of a alkali metal boride tetrafluoride salt including such as KF to lower its melting point is prepared including a dissolved boron containing material, for instance NiB, MnB.sub.2, or CrB.sub.2. A transition metal to be coated is immersed in the melt at a temperature of no more than 700.degree. C. and a surface boride layer of that transition metal is formed within a period of about 24 hours on the substrate surface.

  10. Method of boronizing transition metal surfaces

    DOEpatents

    Koyama, Koichiro; Shimotake, Hiroshi.

    1983-08-16

    A method is presented for preparing a boride layer on a transition metal substrate for use in corrosive environments or as a harden surface in machine applications. This method is particularly useful in treating current collectors for use within a high temperature and corrosive electrochemical cell environment. A melt of a alkali metal boride tetrafluoride salt including such as KF to lower its melting point is prepared including a dissolved boron containing material, for instance NiB, MnB[sub 2], or CrB[sub 2]. A transition metal to be coated is immersed in the melt at a temperature of no more than 700 C and a surface boride layer of that transition metal is formed within a period of about 24 hours on the substrate surface. 4 figs.

  11. Understanding topological phase transition in monolayer transition metal dichalcogenides

    NASA Astrophysics Data System (ADS)

    Choe, Duk-Hyun; Sung, Ha-Jun; Chang, K. J.

    2016-03-01

    Despite considerable interest in layered transition metal dichalcogenides (TMDs), such as M X2 with M =(Mo ,W ) and X =(S ,Se ,Te ) , the physical origin of their topological nature is still poorly understood. In the conventional view of topological phase transition (TPT), the nontrivial topology of electron bands in TMDs is caused by the band inversion between metal d - and chalcogen p -orbital bands where the former is pulled down below the latter. Here, we show that, in TMDs, the TPT is entirely different from the conventional speculation. In particular, M S2 and M S e2 exhibits the opposite behavior of TPT such that the chalcogen p -orbital band moves down below the metal d -orbital band. More interestingly, in M T e2 , the band inversion occurs between the metal d -orbital bands. Our findings cast doubts on the common view of TPT and provide clear guidelines for understanding the topological nature in new topological materials to be discovered.

  12. Synthesis of Schiff base 24-membered trivalent transition metal derivatives with their anti-inflammation and antimicrobial evaluation

    NASA Astrophysics Data System (ADS)

    Kumar, Gajendra; Devi, Shoma; Kumar, Dharmendra

    2016-03-01

    The paper presents the synthesis of macrocyclic complexes [{M(C52H36N12O4)X}X2] of Cr(III), Mn(III) and Fe(III) with Schiff base ligand (C52H36N12O4) obtained through the condensation of 1,4-dicarbonyl phenyl dihydrazide with 1,2-di(1H-indol-1-yl)ethane-1,2-dione. The newly formed Schiff base and its complexes have been characterized with the help of elemental analysis, condensation measurements, magnetic measurements and their structure configuration have been determined by various spectroscopic (electronic, IR, 1H NMR, 13C NMR, GCMS) techniques. The electronic spectra of the complexes indicate a five coordinate square pyramidal geometry of the center metal ion. These metal complexes and ligand were tested for their anti-inflammation and antimicrobial inhibiting potential and compared with standard drugs Phenyl butazone (anti-inflammation), Imipenem (antibacterial) and Miconazole (antifungal).

  13. Synthesis of Nanoporous Iminodiacetic Acid Sorbents for Binding Transition Metals

    PubMed Central

    Busche, Brad; Wiacek, Robert; Davidson, Joseph; Koonsiripaiboon, View; Yantasee, Wassana; Addleman, R. Shane; Fryxell, Glen E.

    2009-01-01

    Iminodiacetic acid (IDAA) forms strong complexes with a wide variety of metal ions. Using self-assembled monolayers in mesoporous supports (SAMMS) to present the IDAA ligand potentially allows for multiple metal-ligand interactions to enhance the metal binding affinity relative to that of randomly oriented polymer-based supports. This manuscript describes the synthesis of a novel nanostructured sorbent material built using self-assembly of a IDAA ligand inside a nanoporous silica, and demonstrates its use for capturing transition metal cations, and anionic metal complexes, such as PdCl4−2. PMID:22068901

  14. Microwave-assisted synthesis of transition metal phosphide

    SciTech Connect

    Viswanathan, Tito

    2014-12-30

    A method of synthesizing transition metal phosphide. In one embodiment, the method has the steps of preparing a transition metal lignosulfonate, mixing the transition metal lignosulfonate with phosphoric acid to form a mixture, and subjecting the mixture to a microwave radiation for a duration of time effective to obtain a transition metal phosphide.

  15. Nuclear Scattering from Transition Metals

    NASA Astrophysics Data System (ADS)

    Hira, Ajit; McKeough, James; Valerio, Mario; Cathey, Tommy

    2016-03-01

    In view of the continued interest in the scattering of light projectiles by metallic nuclei, we present a computational study of the interactions between different nuclear species of atoms such as H through F (Z <= 9) and the nuclei of Silver, Palladium and other metals. Recent work has shown that neutron scattering can be used to record holographic images of materials. We have developed a FORTRAN computer program to compute stopping cross sections and scattering angles in Ag and other metals for the small nuclear projectiles, using Monte Carlo calculation. This code allows for different angles of incidence. Next, simulations were done in the energy interval from 50 to 210 keV. The computational results thus obtained are compared with relevant experimental data. The data are further analyzed to identify periodic trends in terms of the atomic number of the projectile. Such studies also have potential applications in nuclear physics and in nuclear medicine. Funding from National Science Foundation.

  16. Synthesis, characterization and biological activity of transition metal complexes with Schiff bases derived from 2-nitrobenzaldehyde with glycine and methionine

    NASA Astrophysics Data System (ADS)

    Singh, Bibhesh K.; Rajour, Hemant K.; Prakash, Anant

    Schiff bases derived from 2-nitrobenzaldehyde with amino acids (glycine, methionine) and their Co(II), Ni(II) and Cu(II) complexes have been synthesized and characterized by various physico-chemical techniques. From spectral studies, it has been concluded that the ligands acts as bidentate molecule, coordinates metal through azomethine nitrogen and carboxylate oxygen. Mass spectrum explains the successive degradation of the molecular species in solution and justifies ML2 complexes. X-ray powder diffraction helps to determine the cell parameters of the complexes. Molecular structure of the complexes has been optimized by MM2 calculations and suggests a square planar geometry. The ligands and their metal complexes have been tested in vitro against Streptococcus, Staph, Staphylococcus aureus and Escherchia coli bacteria in order to assess their antibacterial potential. The results indicate that the biological activity increases on complexation.

  17. Chemical vapour deposition: Transition metal carbides go 2D

    NASA Astrophysics Data System (ADS)

    Gogotsi, Yury

    2015-11-01

    The unique properties of 2D materials, such as graphene or transition metal dichalcogenides, have been attracting much attention in the past decade. Now, metallically conductive and even superconducting transition metal carbides are entering the game.

  18. Anti-Ambipolar Field-Effect Transistors Based On Few-Layer 2D Transition Metal Dichalcogenides.

    PubMed

    Li, Yongtao; Wang, Yan; Huang, Le; Wang, Xiaoting; Li, Xingyun; Deng, Hui-Xiong; Wei, Zhongming; Li, Jingbo

    2016-06-22

    Two-dimensional (2D) materials and their related van der Waals heterostructures have attracted considerable interest for their fascinating new properties. There are still many challenges in realizing the potential of 2D semiconductors in practical (opto)electronics such as signal transmission and logic circuit, etc. Herein, we report the gate-tunable anti-ambipolar devices on the basis of few-layer transition metal dichalcogenides (TMDs) heterostructures to gain higher information storage density. Our study shows that carrier concentration regulated by the gate voltage plays a major role in the "anti-ambipolar" behavior, where the drain-source current can only pass through in specific range of gate voltage (Vg) and it will be restrained if the Vg goes beyond the range. Several improved strategies were theoretically discussed and experimentally adopted to obtain higher current on/off ratio for the anti-ambipolar devices, such as choosing suitable p-/n-pair, increasing carrier concentration by using thicker-layer TMDs, and so on. The modified SnS2/WSe2 device with the current on/off ratio exceeding 200 and on-state Vg ranging from -20 to 0 V was successfully achieved. On the basis of the anti-ambipolar field-effect transistors (FETs), we also reveal the potential of three-channel device unit for signal processing and information storage. With the equal quantity N of device units, 3(N) digital signals can be obtained from such three-channel devices, which are much larger than 2(N) ones obtained from traditional two-channel complementary metal oxide semiconductors (CMOS). PMID:27258569

  19. Synthesis, characterization and antibacterial activity of a tridentate Schiff base derived from cephalothin and sulfadiazine, and its transition metal complexes

    NASA Astrophysics Data System (ADS)

    Anacona, J. R.; Noriega, Natiana; Camus, Juan

    2015-02-01

    Metal(II) coordination compounds of a cephalothin Schiff base (H2L) derived from the condensation of cephalothin antibiotic with sulfadiazine were synthesized. The Schiff base ligand, mononuclear [ML(H2O)3] (M(II) = Mn, Co, Ni, Zn) complexes and magnetically diluted dinuclear copper(II) complex [CuL(H2O)3]2 were characterized by several techniques, including elemental and thermal analysis, molar conductance and magnetic susceptibility measurements, electronic, FT-IR, EPR and 1H NMR spectral studies. The cephalothin Schiff base ligand H2L behaves as a dianionic tridentate NOO chelating agent. The biological applications of complexes have been studied on two bacteria strains (Escherichia coli and Staphylococcus aureus) by agar diffusion disc method.

  20. Toward Photochemical Water Splitting Using Band-Gap-Narrowed Semiconductors and Transition-Metal Based Molecular Catalysts

    SciTech Connect

    Muckerman,J.T.; Rodriguez, J.A.; Fujita, E.

    2009-06-07

    We are carrying out coordinated theoretical and experimental studies of toward photochemical water splitting using band-gap-narrowed semiconductors (BGNSCs) with attached multi-electron molecular water oxidation and hydrogen production catalysts. We focus on the coupling between the materials properties and the H{sub 2}O redox chemistry, with an emphasis on attaining a fundamental understanding of the individual elementary steps in the following four processes: (1) Light-harvesting and charge-separation of stable oxide or oxide-derived semiconductors for solar-driven water splitting, including the discovery and characterization of the behavior of such materials at the aqueous interface; (2) The catalysis of the four-electron water oxidation by dinuclear hydroxo transition-metal complexes with quinonoid ligands, and the rational search for improved catalysts; (3) Transfer of the design principles learned from the elucidation of the DuBois-type hydrogenase model catalysts in acetonitrile to the rational design of two-electron hydrogen production catalysts for aqueous solution; (4) Combining these three elements to examine the function of oxidation catalysts on BGNSC photoanode surfaces and hydrogen production catalysts on cathode surfaces at the aqueous interface to understand the challenges to the efficient coupling of the materials functions.

  1. A Density Functional Theory Based Protocol to Compute the Redox Potential of Transition Metal Complex with the Correction of Pseudo-Counterion: General Theory and Applications.

    PubMed

    Matsui, Toru; Kitagawa, Yasutaka; Shigeta, Yasuteru; Okumura, Mitsutaka

    2013-07-01

    We propose an accurate scheme to evaluate the redox potential of a wide variety of transition metal complexes by adding a charge-dependent correction term for a counterion around the charged complexes, which is based on Generalized Born theory, to the solvation energy. The mean absolute error (MAE) toward experimental redox potentials of charged complexes is considerably reduced from 0.81 V (maximum error 1.22 V) to 0.22 V (maximum error 0.50 V). We found a remarkable exchange-correlation functional dependence on the results rather than the basis set ones. The combination of Wachters+f (for metal) and 6-31++G(d,p) (for other atoms) with the B3LYP functional gives the least MAE 0.15 V for the test complexes. This scheme is applicable to other solvents, and heavier transition metal complexes such as M1(CO)5(pycn) (M1 = Cr, Mo, W), M2(mnt)2 (M2 = Ni, Pd, Pt), and M3(bpy)3 (M3 = Fe, Ru, Os) with the same quality. PMID:26583980

  2. A structure-based analysis of the vibrational spectra of nitrosyl ligands in transition-metal coordination complexes and clusters

    NASA Astrophysics Data System (ADS)

    De La Cruz, Carlos; Sheppard, Norman

    2011-01-01

    The vibrational spectra of nitrogen monoxide or nitric oxide (NO) bonded to one or to several transition-metal (M) atom(s) in coordination and cluster compounds are analyzed in relation to the various types of such structures identified by diffraction methods. These structures are classified in: (a) terminal (linear and bent) nitrosyls, [M(σ-NO)] or [M(NO)]; (b) twofold nitrosyl bridges, [M 2(μ 2-NO)]; (c) threefold nitrosyl bridges, [M 3(μ 3-NO)]; (d) σ/π-dihaptonitrosyls or " side-on" nitrosyls; and (e) isonitrosyls (oxygen-bonded nitrosyls). Typical ranges for the values of internuclear N-O and M-N bond-distances and M-N-O bond-angles for linear nitrosyls are: 1.14-1.20 Å/1.60-1.90 Å/180-160° and for bent nitrosyls are 1.16-1.22 Å/1.80-2.00 Å/140-110°. The [M 2(μ 2-NO)] bridges have been divided into those that contain one or several metal-metal bonds and those without a formal metal/metal bond (M⋯M). Typical ranges for the M-M, N-O, M-N bond distances and M-N-M bond angles for the normal twofold NO bridges are: 2.30-3.00 Å/1.18-1.22 Å/1.80-2.00 Å/90-70°, whereas for the analogous ranges of the long twofold NO bridges these are 3.10-3.40 Å/1.20-1.24 Å/1.90-2.10 Å/130-110°. In both situations the N-O vector is approximately at right angle to the M-M (or M⋯M) vector within the experimental error; i.e. the NO group is symmetrical bonded to the two metal atoms. In contrast the threefold NO bridges can be symmetrically or unsymmetrically bonded to an M 3-plane of a cluster compound. Characteristic values for the N-O and M-N bond-distances of these NO bridges are: 1.24-1.28 Å/1.80-1.90 Å, respectively. As few dihaptonitrosyl and isonitrosyl complexes are known, the structural features of these are discussed on an individual basis. The very extensive vibrational spectroscopy literature considered gives emphasis to the data from linearly bonded NO ligands in stable closed-shell metal complexes; i.e. those which are consistent with the

  3. A structure-based analysis of the vibrational spectra of nitrosyl ligands in transition-metal coordination complexes and clusters.

    PubMed

    De La Cruz, Carlos; Sheppard, Norman

    2011-01-01

    The vibrational spectra of nitrogen monoxide or nitric oxide (NO) bonded to one or to several transition-metal (M) atom(s) in coordination and cluster compounds are analyzed in relation to the various types of such structures identified by diffraction methods. These structures are classified in: (a) terminal (linear and bent) nitrosyls, [M(σ-NO)] or [M(NO)]; (b) twofold nitrosyl bridges, [M2(μ2-NO)]; (c) threefold nitrosyl bridges, [M3(μ3-NO)]; (d) σ/π-dihaptonitrosyls or "side-on" nitrosyls; and (e) isonitrosyls (oxygen-bonded nitrosyls). Typical ranges for the values of internuclear N-O and M-N bond-distances and M-N-O bond-angles for linear nitrosyls are: 1.14-1.20 Å/1.60-1.90 Å/180-160° and for bent nitrosyls are 1.16-1.22 Å/1.80-2.00 Å/140-110°. The [M2(μ2-NO)] bridges have been divided into those that contain one or several metal-metal bonds and those without a formal metal/metal bond (M⋯M). Typical ranges for the M-M, N-O, M-N bond distances and M-N-M bond angles for the normal twofold NO bridges are: 2.30-3.00 Å/1.18-1.22 Å/1.80-2.00 Å/90-70°, whereas for the analogous ranges of the long twofold NO bridges these are 3.10-3.40 Å/1.20-1.24 Å/1.90-2.10 Å/130-110°. In both situations the N-O vector is approximately at right angle to the M-M (or M⋯M) vector within the experimental error; i.e. the NO group is symmetrical bonded to the two metal atoms. In contrast the threefold NO bridges can be symmetrically or unsymmetrically bonded to an M3-plane of a cluster compound. Characteristic values for the N-O and M-N bond-distances of these NO bridges are: 1.24-1.28 Å/1.80-1.90 Å, respectively. As few dihaptonitrosyl and isonitrosyl complexes are known, the structural features of these are discussed on an individual basis. The very extensive vibrational spectroscopy literature considered gives emphasis to the data from linearly bonded NO ligands in stable closed-shell metal complexes; i.e. those which are consistent with the

  4. Transition-metal substitutions in iron chalcogenides

    NASA Astrophysics Data System (ADS)

    Bezusyy, V. L.; Gawryluk, D. J.; Malinowski, A.; Cieplak, Marta Z.

    2015-03-01

    The a b -plane resistivity and Hall effect are studied in Fe1 -yMyTe0.65Se0.35 single crystals doped with two transition-metal elements, M = Co or Ni, over a wide doping range, 0 ≤y ≤0.2 . The superconducting transition temperature, Tc, reaches zero for Co at y ≃0.14 and for Ni at y ≃0.032 , while the resistivity at the Tc onset increases weakly with Co doping, and strongly with Ni doping. The Hall coefficient RH, positive for y =0 , remains so at high temperatures for all y , while it changes sign to negative at low T for y >0.135 (Co) and y >0.06 (Ni). The analysis based on a two-band model suggests that at high T residual hole pockets survive the doping, but holes get localized upon the lowering of T , so that the effect of the electron doping on the transport becomes evident. The suppression of the Tc by Co impurity is related to electron doping, while in the case of the Ni impurity strong electron localization most likely contributes to fast decrease of the Tc.

  5. Transition Metal Phosphide Hydroprocessing Catalysts: A review

    SciTech Connect

    Oyama, S.; Gott, T; Zhao, H; Lee, Y

    2009-01-01

    The diminishing quality of oil feedstocks coupled with increasingly more stringent environmental regulations limiting the content of sulfur in transportation fuels have given rise to a need for improved hydroprocessing technology. This review begins with a summary of the major improvements in hydrodesulfurization (HDS) and hydrodenitrogenation (HDN) catalysts and processes that have been reported in recent years. It then describes a new class of hydroprocessing catalysts, the transition metal phosphides, which have emerged as a promising group of high-activity, stable catalysts. The phosphides have physical properties resembling ceramics, so are strong and hard, yet retain electronic and magnetic properties similar to metals. Their crystal structures are based on trigonal prisms, yet they do not form layered structures like the sulfides. They display excellent performance in HDS and HDN, with the most active phosphide, Ni{sub 2}P, having activity surpassing that of promoted sulfides on the basis of sites titrated by chemisorption (CO for the phosphides, O{sub 2} for the sulfides). In the HDS of difficult heteroaromatics like 4,6-dimethyldibenzothiophene Ni{sub 2}P operates by the hydrogenation pathway, while in the HDN of substituted nitrogen compounds like 2-methylpiperidine it carries out nucleophilic substitution. The active sites for hydrogenation in Ni{sub 2}P have a square pyramidal geometry, while those for direct hydrodesulfurization have a tetrahedral geometry. Overall, Ni{sub 2}P is a promising catalyst for deep HDS in the presence of nitrogen and aromatic compounds.

  6. Dimensional diversity in transition metal trihalides

    SciTech Connect

    Jianhua Lin; Miller, G.J. )

    1993-04-14

    Structural variations of the second- and third-row transition metal trihalides are rationalized via tight-binding band calculations and evaluation of Madelung energetic factors. The observed structure for a given metal halide is controlled by both the coordination geometry at the anion and the d electron configuration at the metal. As the polarizability of the halide increases, the M-X-M angle, in general, decreases so that three-dimensional frameworks occur for the fluorides, while layer and chain structures are found for the chlorides, bromides, and iodides. Within a particular halide system, systematic structural trends also occur as the d electron configuration changes. 56 refs., 23 figs., 4 tabs.

  7. OH-transition metal bonding

    NASA Technical Reports Server (NTRS)

    Bauschlicher, Charles W., Jr.

    1986-01-01

    The bonding in both CuOH and AgOH has a covalent component that leads to a bent structure. The larger electrostatic stabilization in CuOH leads to a larger D(e) (2.83 eV) compared with AgOH (2.20 eV). Using Ni5OH to model chemisorption of OH on a Ni surface, it is found that OH adsorption in the fourfold hollow of Ni(100) leads to an OH normal to the surface, while adsorption directly above a Ni atom leads to a tilted OH. These qualitative Ni5OH calculations allow for speculation on the observed variation of OH on metal surfaces.

  8. Synthesis, spectral, antimicrobial and antitumor assessment of Schiff base derived from 2-aminobenzothiazole and its transition metal complexes

    NASA Astrophysics Data System (ADS)

    Etaiw, Safaa Eldin H.; Abd El-Aziz, Dina M.; Abd El-Zaher, Eman H.; Ali, Elham A.

    2011-09-01

    N-(thiophen-2-ylmethylene)benzo[ d]thiazol-2-amine Schiff base (L) derived from 2-aminobenzothiazole and 2-thiophenecarboxaldehyde was synthesized and characterized using elemental analysis, IR, mass spectra, 1H NMR and UV-vis spectra. Its complexes with Cu(II), Fe(III), Ni(II) and Zn(II) were prepared and isolated as solid products and characterized by elemental and thermal analyses, spectral techniques as well as magnetic susceptibility. The IR spectra showed that the Schiff base under investigation behaves as bidentate ligand. The UV-vis spectra and magnetic moment data suggested octahedral geometry around Cu(II) and Fe(III) and tetrahedral geometry around Ni(II) and Zn(II). In view of the biological activity of the Schiff base and its complexes, it has been observed that the antimicrobial activity of the Schiff base increased on complexation with the metal ion. In vitro antitumor activity assayed against five human tumor cell lines furnished the significant toxicities of the Schiff base and its complexes.

  9. High Pressure Synthesis of Transition Metal Carbonyls.

    ERIC Educational Resources Information Center

    Hagen, A. P.; And Others

    1979-01-01

    Presents an experiment which uses readily available starting materials and inexpensive equipment for synthesis of transition metal carbonyls at 1000 atm and which is intended to give students experience in techniques used in research and industry. Safety precautions are emphasized. (Author/SA)

  10. Five novel transition metal coordination polymers with 2D/3D framework structure based on flexible H{sub 2}tzda and ancillary ligand bpe

    SciTech Connect

    Wang Yuting; Xu Yan; Fan Yaoting; Hou Hongwei

    2009-10-15

    Five new transition metal coordination polymers based on H{sub 2}tzda and co-ligand bpe, {l_brace}[M(tzda)(bpe)].H{sub 2}O{r_brace}{sub n} [M=Zn(1), Cd(2), Mn(3), Co(4)] and [Ni{sub 2}(tzda){sub 2}(bpe){sub 2}(H{sub 2}O)]{sub n} (5) [H{sub 2}tzda=(1,3,4-thiadiazole-2,5-diyldithio)diacetic acid, bpe=1,2-bis(4-pyridyl)ethane], have been hydrothermally synthesized and structurally characterized. Compounds 1-4 feature a 2D-layered architecture generated from [M(tzda)]{sub n} moiety with double-chain structure cross-linking bpe spacers. However, the conformations bpe adopts in 3 and 4 are different from those in 1 and 2 due to the rotation of C-C single bond in bpe. Polymer 5 exhibits an interesting 3D porous framework with 2-fold interpenetration, in which intriguing 1D double helix chains are observed. The photoluminescence properties of 1 and 2 in the solid-state at room temperature are investigated. In addition, variable-temperature magnetic data show weak antiferromagnetic behavior in 3-5. - Graphical abstract: Five new transition metal coordination polymers based on flexible H{sub 2}tzda and bpe have been hydrothermally synthesized and characterized by X-ray diffraction, luminescent emission spectra and low-temperature magnetic measurements, respectively.

  11. Pristine and intercalated transition metal dichalcogenide superconductors

    NASA Astrophysics Data System (ADS)

    Klemm, Richard A.

    2015-07-01

    Transition metal dichalcogenides (TMDs) are quasi-two-dimensional layered compounds that exhibit strongly competing effects of charge-density wave (CDW) formation and superconductivity (SC). The weak van der Waals interlayer bonding between hexagonal layers of octahedral or trigonal prismatic TMD building blocks allows many polytypes to form. In the single layer 1 T polytype materials, one or more CDW states can form, but the pristine TMDs are not superconducting. The 2 H polytypes have two or more Fermi surfaces and saddle bands, allowing for dual orderings, which can be coexisting CDW and SC orderings, two SC gaps as in MgB2, two CDW gaps, and possibly even pseudogaps above the onset TCDW s of CDW orderings. Higher order polytypes allow for multiple CDW gaps and at least one superconducting gap. The CDW transitions TCDW s usually greatly exceed the superconducting transitions at their low Tc values, their orbital order parameters (OPs) are generally highly anisotropic and can even contain nodes, and the SC OPs can be greatly affected by their simultaneous presence. The properties of the CDWs ubiquitously seen in TMDs are remarkably similar to those of the pseudogaps seen in the high-Tc cuprates. In 2H-NbSe2, for example, the CDW renders its general s-wave SC OP orbital symmetry to be highly anisotropic and strongly reduces its Josephson coupling strength (IcRn) with the conventional SC, Pb. Hence, the pristine TMDs are highly "unconventional" in comparison with Pb, but are much more "conventional" than are the ferromagnetic superconductors such as URhGe. Applied pressure and intercalation generally suppress the TMD CDWs, allowing for enhanced SC formation, even in the 1 T polytype materials. The misfit intercalation compound (LaSe)1.14(NbSe2) and many 2 H -TMDs intercalated with organic Lewis base molecules, such as TaS2(pyridine)1/2, have completely incoherent c-axis transport, dimensional-crossover effects, and behave as stacks of intrinsic Josephson junctions

  12. I. Gas adsorption properties and porosity of transition metal-based cyanogels. II. Novel energy transfer processes in organic light-emitting devices

    NASA Astrophysics Data System (ADS)

    Deshpande, Rahul Shrikant

    The gas adsorption properties and porosity of cyanide-bridged transition metal-based gels are investigated in the first part of this dissertation. The cyanide bridges, connecting two transition metal centers, are characteristic of these gels; hence, these gels are termed cyanogels. Aerogel versus xerogel structures have a profound effect, both, on the thermodynamics and kinetics of gas adsorption on these cyanogels. Carbon dioxide is selectively adsorbed on palladium-cobalt-based cyanogels; the adsorption is fully reversible on both types of gels discussed. The thermodynamics and kinetics of the gas adsorption processes on these gels are analyzed here. From the ease and reproducibility of the CO2 desorption and the associated enthalpy values, it is concluded that CO2 is physisorbed on these gels. Both the adsorption and desorption processes are first-order in the gels. Adsorption of carbon monoxide on the palladium-cobalt cyanogels is also investigated. Unlike CO 2 physisorption, carbon monoxide is chemisorbed on these gels. An uptake of CO brings about a profound change in the xerogel morphology. The palladium-cobalt-based aerogels possess both micro- and mesoporosity; the xerogels are predominantly microporous with a narrow microporosity. The aerogel surfaces are found to be fractal as analyzed by gas adsorption. Unlike the aerogels, the xerogels do not possess surface fractality. The mechanism of adsorption of different gases on these gels is analyzed based on the gel morphologies. These transition metal-based gels are promising for a variety of applications such as heterogeneous catalysts, gas filters and magnetic materials. The porosity of these gels can be exploited to make gel-embedded filters to separate mixtures of gases based on the their differential adsorption propensities. The reversible adsorption of CO2 can be harnessed practically by using these gels as CO2 storage reservoirs. In the second part of this dissertation, the first, balanced, white

  13. Iodide effects in transition metal catalyzed reactions.

    PubMed

    Maitlis, Peter M; Haynes, Anthony; James, Brian R; Catellani, Marta; Chiusoli, Gian Paolo

    2004-11-01

    The unique properties of I(-) allow it to be involved in several different ways in reactions catalyzed by the late transition metals: in the oxidative addition, the migration, and the coupling/reductive elimination steps, as well as in substrate activation. Most steps are accelerated by I(-)(for example through an increased nucleophilicity of the metal center), but some are retarded, because a coordination site is blocked. The "soft" iodide ligand binds more strongly to soft metals (low oxidation state, electron rich, and polarizable) such as the later and heavier transition metals, than do the other halides, or N- and O-centered ligands. Hence in a catalytic cycle that includes the metal in a formally low oxidation state there will be less tendency for the metal to precipitate (and be removed from the cycle) in the presence of I(-) than most other ligands. Iodide is a good nucleophile and is also easily and reversibly oxidized to I(2). In addition, I(-) can play key roles in purely organic reactions that occur as part of a catalytic cycle. Thus to understand the function of iodide requires careful analysis, since two or sometimes more effects occur in different steps of one single cycle. Each of these topics is illustrated with examples of the influence of iodide from homogeneous catalytic reactions in the literature: methanol carbonylation to acetic acid and related reactions; CO hydrogenation; imine hydrogenation; and C-C and C-N coupling reactions. General features are summarised in the Conclusions. PMID:15510253

  14. Flexible transition metal dichalcogenide nanosheets for band-selective photodetection

    PubMed Central

    Velusamy, Dhinesh Babu; Kim, Richard Hahnkee; Cha, Soonyoung; Huh, June; Khazaeinezhad, Reza; Kassani, Sahar Hosseinzadeh; Song, Giyoung; Cho, Suk Man; Cho, Sung Hwan; Hwang, Ihn; Lee, Jinseong; Oh, Kyunghwan; Choi, Hyunyoug; Park, Cheolmin

    2015-01-01

    The photocurrent conversions of transition metal dichalcogenide nanosheets are unprecedentedly impressive, making them great candidates for visible range photodetectors. Here we demonstrate a method for fabricating micron-thick, flexible films consisting of a variety of highly separated transition metal dichalcogenide nanosheets for excellent band-selective photodetection. Our method is based on the non-destructive modification of transition metal dichalcogenide sheets with amine-terminated polymers. The universal interaction between amine and transition metal resulted in scalable, stable and high concentration dispersions of a single to a few layers of numerous transition metal dichalcogenides. Our MoSe2 and MoS2 composites are highly photoconductive even at bending radii as low as 200 μm on illumination of near infrared and visible light, respectively. More interestingly, simple solution mixing of MoSe2 and MoS2 gives rise to blended composite films in which the photodetection properties were controllable. The MoS2/MoSe2 (5:5) film showed broad range photodetection suitable for both visible and near infrared spectra. PMID:26333531

  15. Hybrid uranium-transition-metal oxide cage clusters.

    PubMed

    Ling, Jie; Hobbs, Franklin; Prendergast, Steven; Adelani, Pius O; Babo, Jean-Marie; Qiu, Jie; Weng, Zhehui; Burns, Peter C

    2014-12-15

    Transition-metal based polyoxometalate clusters have been known for decades, whereas those built from uranyl peroxide polyhedra have more recently emerged as a family of complex clusters. Here we report the synthesis and structures of six nanoscale uranyl peroxide cage clusters that contain either tungstate or molybdate polyhedra as part of the cage, as well as phosphate tetrahedra. These transition-metal-uranium hybrid clusters exhibit unique polyhedral connectivities and topologies that include 6-, 7-, 8-, 10-, and 12-membered rings of uranyl polyhedra and uranyl ions coordinated by bidentate peroxide in both trans and cis configurations. The transition-metal polyhedra appear to stabilize unusual units built of uranyl polyhedra, rather than templating their formation. PMID:25434424

  16. Insulator to Metal Transition in Fluid Hydrogen

    SciTech Connect

    Hood, R Q; Galli, G

    2003-06-15

    The authors have investigated the insulator to metal transition (ITM) in fluid hydrogen using first principles simulations. Both density functional and quantum Monte Carlo calculations show that the electronic energy gap of the liquid vanishes at about 9 fold compression and 3000 K. At these conditions the computed conductivity values are characteristic of a poor metal. These findings are consistent with those of recent shock wave experiments but the computed conductivity is larger than the measured value. From the ab-initio results they conclude that the ITM is driven by molecular dissociation rather than disorder and that both temperature and pressure play a key role in determining structural changes in the fluid.

  17. DNA binding and recognition by binuclear transition metal complexes

    NASA Astrophysics Data System (ADS)

    Liu, Changlin; Yan, Rui; Xu, Yan; Yu, Siwang; Liao, Zhanru; Li, Dongfeng; Xu, Hui-Bie F.

    2001-09-01

    The development of small molecules that can bind and recognize DNA with sequence- or stereo-specificity under physiological conditions has been attracting a great interest in chemistry and biochemistry. Here, spectroscopic characterization and gel electrophoresis methods have been utilized to investigate the DNA binding and recognition by a variety of binuclear transition metal complexes. The result indicate that the structures and charges of binuclear transition metal complexes, compositions of coordination spheres, central metal ions and their coordination unsaturation, and separations between two central metal atoms can exert significant effects on the DNA binding and recognition. If there are not intercalative ligands into DNA base pairs or kinetically substitutable ligands by DNA phosphate groups within coordination sphere, the coordination saturation and compact binuclear transition metal complexes weaker bind to DNA than the coordination unsaturation and extended ones to DNA. Since the different transtiometal ions exhibit different affinities to DNA phosphate oxygen atoms, the binding interactions between their binuclear complexes and DNA are controlled by the affinity. He binuclear complexes with one or more negative charges lead to a consequence that they can not efficient associate with DNA, because DNA phosphodiester backbone is negatively charged. Whenthe separations between two central transition metal atoms is more than the distance between two DNA base pairs, the binuclear complexes could bind and recognize the DNA sequence with two or more base pairs. The protonated and positively charged ligands can strengthen the DNA binding and recognition by these binuclear metal complexes. Based on such DNA binding and recognition principles, the binuclear zinc complex designed in the study preferentially bind and recognize the following DNA sequence on pBR322 DNA with binding constant K.

  18. Probing the possibility of coexistence of martensite transition and half-metallicity in Ni and Co-based full-Heusler alloys: An ab initio calculation

    NASA Astrophysics Data System (ADS)

    Roy, Tufan; Pandey, Dhanshree; Chakrabarti, Aparna

    2016-05-01

    Using first-principles calculations based on density functional theory, we have studied the mechanical, electronic, and magnetic properties of Heusler alloys, namely, Ni2B C and Co2B C (B = Sc, Ti, V, Cr, and Mn as well as Y, Zr, Nb, Mo, and Tc; C = Ga and Sn). On the basis of electronic structure (density of states) and mechanical properties (tetragonal shear constant), as well as magnetic interactions (Heisenberg exchange coupling parameters), we probe the properties of these materials in detail. We calculate the formation energy of these alloys in the (face-centered) cubic austenite structure to probe the stability of all these materials. From the energetic point of view, we have studied the possibility of the electronically stable alloys having a tetragonal phase lower in energy compared to the respective cubic phase. A large number of the magnetic alloys is found to have the cubic phase as their ground state. On the other hand, for another class of alloys, the tetragonal phase has been found to have lower energy compared to the cubic phase. Further, we find that the values of tetragonal shear constant show a consistent trend: a high positive value for materials not prone to tetragonal transition and low or negative for others. In the literature, materials which have been seen to undergo the martensite transition are found to be metallic in nature. We probe here if there is any Heusler alloy which has a tendency to undergo a tetragonal transition and at the same time possesses a high spin polarization at the Fermi level. From our study, it is found that out of the four materials which exhibit a martensite phase as their ground state, three of these, namely, Ni2MnGa , Ni2MoGa , and Co2NbSn have a metallic nature; on the contrary, Co2MoGa exhibits a high spin polarization.

  19. Properties of Transition Metal Doped Alumina

    NASA Astrophysics Data System (ADS)

    Nykwest, Erik; Limmer, Krista; Brennan, Ray; Blair, Victoria; Ramprasad, Rampi

    Crystallographic texture can have profound effects on the properties of a material. One method of texturing is through the application of an external magnetic field during processing. While this method works with highly magnetic systems, doping is required to couple non-magnetic systems with the external field. Experiments have shown that low concentrations of rare earth (RE) dopants in alumina powders have enabled this kind of texturing. The magnetic properties of RE elements are directly related to their f orbital, which can have as many as 7 unpaired electrons. Since d-block elements can have as many as 5 unpaired electrons the effects of substitutional doping of 3d transition metals (TM) for Al in alpha (stable) and theta (metastable) alumina on the local structure and magnetic properties, in addition to the energetic cost, have been calculated by performing first-principles calculations based on density functional theory. This study has led to the development of general guidelines for the magnetic moment distribution at and around the dopant atom, and the dependence of this distribution on the dopant atom type and its coordination environment. It is anticipated that these findings can aid in the selection of suitable dopants help to guide parallel experimental efforts. This project was supported in part by an internship at the Army Research Laboratory, administered by the Oak Ridge Institute for Science and Education, along with a grant of computer time from the DoD High Performance Computing Modernization Program.

  20. Exciton formation in monolayer transition metal dichalcogenides.

    PubMed

    Ceballos, Frank; Cui, Qiannan; Bellus, Matthew Z; Zhao, Hui

    2016-06-01

    Two-dimensional transition metal dichalcogenides provide a unique platform to study excitons in confined structures. Recently, several important aspects of excitons in these materials have been investigated in detail. However, the formation process of excitons from free carriers has yet to be understood. Here we report time-resolved measurements on the exciton formation process in monolayer samples of MoS2, MoSe2, WS2, and WSe2. The free electron-hole pairs, injected by an ultrashort laser pulse, immediately induce a transient absorption signal of a probe pulse tuned to the exciton resonance. The signal quickly drops by about a factor of two within 1 ps and is followed by a slower decay process. In contrast, when excitons are resonantly injected, the fast decay component is absent. Based both on its excitation excess energy and intensity dependence, this fast decay process is attributed to the formation of excitons from the electron-hole pairs. This interpretation is also consistent with a model that shows how free electron-hole pairs can be about twice more effective than excitons in altering the exciton absorption strength. From our measurements and analysis of our results, we determined that the exciton formation times in these monolayers to be shorter than 1 ps. PMID:27219022

  1. Energetic characteristics of transition metal complexes.

    PubMed

    Wojewódka, Andrzej; Bełzowski, Janusz; Wilk, Zenon; Staś, Justyna

    2009-11-15

    Ten transition metal nitrate and perchlorate complexes of hydrazine and ethylenediamine were synthesized, namely [Cu(EN)(2)](ClO(4))(2), [Co(EN)(3)](ClO(4))(3), [Ni(EN)(3)](ClO(4))(2), [Hg(EN)(2)](ClO(4))(2), [Cr(N(2)H(4))(3)](ClO(4))(3), [Cd(N(2)H(4))(3)](ClO(4))(2), [Ni(N(2)H(4))(3)](NO(3))(2), [Co(N(2)H(4))(3)](NO(3))(3), [Zn(N(2)H(4))(3)](NO(3))(2), and [Cd(N(2)H(4))(3)](NO(3))(2) based on the lines of the literature reported methods. All of them were tested with applying underwater detonation test and further compared to the typical blasting explosives: RDX, HMX, TNT and PETN. From the above presented complexes [Ni(N(2)H(4))(3)](NO(3))(2) (called NHN) and [Co(N(2)H(4))(3)](NO(3))(3) (called CoHN) are known as primary explosives and can be used as the standard explosives. Explosion parameters, such as shock wave overpressure, shock wave energy equivalent and bubble energy equivalent, were determined. Evaluated energetic characteristics of the tested compounds are comparable to those of the classic high explosives and are even enhanced in some cases. PMID:19631466

  2. Exciton formation in monolayer transition metal dichalcogenides

    NASA Astrophysics Data System (ADS)

    Ceballos, Frank; Cui, Qiannan; Bellus, Matthew Z.; Zhao, Hui

    2016-06-01

    Two-dimensional transition metal dichalcogenides provide a unique platform to study excitons in confined structures. Recently, several important aspects of excitons in these materials have been investigated in detail. However, the formation process of excitons from free carriers has yet to be understood. Here we report time-resolved measurements on the exciton formation process in monolayer samples of MoS2, MoSe2, WS2, and WSe2. The free electron-hole pairs, injected by an ultrashort laser pulse, immediately induce a transient absorption signal of a probe pulse tuned to the exciton resonance. The signal quickly drops by about a factor of two within 1 ps and is followed by a slower decay process. In contrast, when excitons are resonantly injected, the fast decay component is absent. Based both on its excitation excess energy and intensity dependence, this fast decay process is attributed to the formation of excitons from the electron-hole pairs. This interpretation is also consistent with a model that shows how free electron-hole pairs can be about twice more effective than excitons in altering the exciton absorption strength. From our measurements and analysis of our results, we determined that the exciton formation times in these monolayers to be shorter than 1 ps.

  3. Magnetic and Metal-Insulator Transition in natural Transition Metal Sulfides

    NASA Astrophysics Data System (ADS)

    Wang, Renxiong; Metz, Tristin; Liu, I.-Lin; Wang, Kefeng; Wang, Xiangfeng; Jeffries, J. R.; Saha, S. R.; Greene, R. L.; Paglione, J.; Santelli, C. C.; Post, J.,

    In collaboration with the Smithsonian Institution's National Museum of Natural History, we present detailed studies of a class of natural minerals with potential to harbor correlated behavior. Transition metal sulfide minerals, such as Bornite (Cu5FeS4), are an important family of compounds known for their thermoelectric properties. We will present low temperature experimental studies of magnetic transitions and focus on a compound that exhibits a metal to insulator transition concident with entrance to an antiferromagnetic ground state, suggesting a potentially interesting system with promise for realizing new correlated states of matter in a naturally occurring mineral.

  4. (Electronic structure and reactivities of transition metal clusters)

    SciTech Connect

    Not Available

    1992-01-01

    The following are reported: theoretical calculations (configuration interaction, relativistic effective core potentials, polyatomics, CASSCF); proposed theoretical studies (clusters of Cu, Ag, Au, Ni, Pt, Pd, Rh, Ir, Os, Ru; transition metal cluster ions; transition metal carbide clusters; bimetallic mixed transition metal clusters); reactivity studies on transition metal clusters (reactivity with H{sub 2}, C{sub 2}H{sub 4}, hydrocarbons; NO and CO chemisorption on surfaces). Computer facilities and codes to be used, are described. 192 refs, 13 figs.

  5. Cascade morphology transition in bcc metals.

    PubMed

    Setyawan, Wahyu; Selby, Aaron P; Juslin, Niklas; Stoller, Roger E; Wirth, Brian D; Kurtz, Richard J

    2015-06-10

    Energetic atom collisions in solids induce shockwaves with complex morphologies. In this paper, we establish the existence of a morphological transition in such cascades. The order parameter of the morphology is defined as the exponent, b, in the defect production curve as a function of cascade energy (N(F) ~ E(MD)(b)). Response of different bcc metals can be compared in a consistent energy domain when the energy is normalized by the transition energy, μ, between the high- and the low-energy regime. Using Cr, Fe, Mo and W data, an empirical formula of μ as a function of displacement threshold energy, E(d), is presented for bcc metals. PMID:25985256

  6. Cascade morphology transition in bcc metals

    SciTech Connect

    Setyawan, Wahyu; Selby, A.; Juslin, Niklas; Stoller, Roger E.; Wirth, Brian D.; Kurtz, Richard J.

    2015-06-10

    Energetic atom collisions in solids induce shockwaves with complex morphologies. In this paper, we establish the existence of a morphological transition in such cascades. The order parameter of the morphology is defined as the exponent, $b$, in the defect production curve as a function of cascade energy ($N_F$$ \\sim$$E_{MD}^b$). Response of different bcc metals can be compared in a consistent energy domain when the energy is normalized by the transition energy, $\\mu$, between the high- and the low-energy regime. Using Cr, Fe, Mo and W data, an empirical formula of $\\mu$ as a function of displacement threshold energy, $E_d$, is presented for bcc metals.

  7. Topological phase transition in layered transition metal dichalcogenides

    NASA Astrophysics Data System (ADS)

    Choe, Duk-Hyun; Sung, Ha-Jun; Chang, Kee Joo

    Despite considerable interests in transition metal dichalcogenides (TMDs), such as MX2 with M = (Mo, W) and X = (S, Se, Te), the physical origin of their topological nature is still in its infancy. The conventional view of topological phase transition (TPT) in TMDs is that the band inversion occurs between the metal d and chalcogen p orbital bands. More precisely, the former is pulled down below the latter. Here we introduce an explicit scheme for analyzing TPT in topological materials and find that the TPT in TMDs is different from the conventional speculation. When the 1T phase undergoes a structural transformation to the 1T' phase in monolayer MX2, the band topology changes from trivial to non-trivial, leading to the TPT. We discuss the exact role of the metal d and chalcogen p orbital bands during the TPT. Our finding would provide clear guidelines for understanding the topological nature not only in TMDs but also in other topological materials yet to be explored.

  8. Single-layer transition metal sulfide catalysts

    DOEpatents

    Thoma, Steven G.

    2011-05-31

    Transition Metal Sulfides (TMS), such as molybdenum disulfide (MoS.sub.2), are the petroleum industry's "workhorse" catalysts for upgrading heavy petroleum feedstocks and removing sulfur, nitrogen and other pollutants from fuels. We have developed an improved synthesis technique to produce SLTMS catalysts, such as molybdenum disulfide, with potentially greater activity and specificity than those currently available. Applications for this technology include heavy feed upgrading, in-situ catalysis, bio-fuel conversion and coal liquefaction.

  9. Corrosion behavior of mesoporous transition metal nitrides

    SciTech Connect

    Yang, Minghui; Allen, Amy J.; Nguyen, Minh T.; Ralston, Walter T.; MacLeod, Michelle J.; DiSalvo, Francis J.

    2013-09-15

    Transition metal nitrides (TMN) have many desirable characteristics such as high hardness and good thermal stability under reducing conditions. This work reports an initial survey of the chemical stability of mesoporous TMNs (TM=Nb, V, Cr and Ti) in water at 80 °C at neutral, acidic and alkaline pH. The mesoporous TMNs had specific surface areas of 25–60 m{sup 2}/g with average pore sizes ranging from 10 to 50 nm. The high surface areas of these materials enhance the rate of corrosion per unit mass over that of a bulk material, making detection of corrosion much easier. The products were characterized by Rietveld refinement of powder X-ray diffraction (PXRD) patterns and by scanning electron microscopy (SEM). Several nitrides have corrosion rates that are, within error, not distinguishable from zero (±1 Å/day). Of the nitrides examined, CrN appears to be the most corrosion resistant under acidic conditions. None of the nitrides studied are corrosion resistant under alkaline conditions. - Graphical abstract: Corrosion behavior of mesoporous transition metal nitrides (TM=Nb, V, Cr and Ti) in acidic and alkaline solutions at 80 °C for 2 weeks. Display Omitted - highlights: • Corrosion rates of mesoporous transition metal nitrides in aqueous solution is reported. • The mesoporous TMNs had surface areas of 25–60 m{sup 2}/g. • CrN is the most corrosion resistant under the conditions studied.

  10. Aging of Transition Metal Dichalcogenide Monolayers.

    PubMed

    Gao, Jian; Li, Baichang; Tan, Jiawei; Chow, Phil; Lu, Toh-Ming; Koratkar, Nikhil

    2016-02-23

    Two-dimensional sheets of transition metal dichalcogenides are an emerging class of atomically thin semiconductors that are considered to be "air-stable", similar to graphene. Here we report that, contrary to current understanding, chemical vapor deposited transition metal dichalcogenide monolayers exhibit poor long-term stability in air. After room-temperature exposure to the environment for several months, monolayers of molybdenum disulfide and tungsten disulfide undergo dramatic aging effects including extensive cracking, changes in morphology, and severe quenching of the direct gap photoluminescence. X-ray photoelectron and Auger electron spectroscopy reveal that this effect is related to gradual oxidation along the grain boundaries and the adsorption of organic contaminants. These results highlight important challenges associated with the utilization of transition metal dichalcogenide monolayers in electronic and optoelectronic devices. We also demonstrate a potential solution to this problem, featuring encapsulation of the monolayer sheet by a 10-20 nm thick optically transparent polymer (parylene C). This strategy is shown to successfully prevent the degradation of the monolayer material under accelerated aging (i.e., high-temperature, oxygen-rich) conditions. PMID:26808328

  11. Catabolism of hyaluronan: involvement of transition metals

    PubMed Central

    Šoltés, Ladislav; Kogan, Grigorij

    2009-01-01

    One of the very complex structures in the vertebrates is the joint. The main component of the joint is the synovial fluid with its high-molar-mass glycosaminoglycan hyaluronan, which turnover is approximately twelve hours. Since the synovial fluid does not contain any hyaluronidases, the fast hyaluronan catabolism is caused primarily by reductive-oxidative processes. Eight transition metals – V23, Mn25, Fe26, Co27, Ni28, Cu29, Zn30, and Mo42 – naturally occurring in living organism are essential for the control of various metabolic and signaling pathways. They are also the key elements in catabolism of hyaluronan in the joint. In this overview, the role of these metals in physiological and pathophysiological catabolism of hyaluronan is described. The participation of these metals in the initiation and propagation of the radical degradation hyaluronan is critically reviewed. PMID:21217859

  12. Transition Metal Nitrides for Electrocatalytic Energy Conversion: Opportunities and Challenges.

    PubMed

    Xie, Junfeng; Xie, Yi

    2016-03-01

    Electrocatalytic energy conversion has been considered as one of the most efficient and promising pathways for realizing energy storage and energy utilization in modern society. To improve electrocatalytic reactions, specific catalysts are needed to lower the overpotential. In the search for efficient alternatives to noble metal catalysts, transition metal nitrides have attracted considerable interest due to their high catalytic activity and unique electronic structure. Over the past few decades, numerous nitride-based catalysts have been explored with respect to their ability to drive various electrocatalytic reactions, such as the hydrogen evolution reaction and the oxygen evolution reaction to achieve water splitting and the oxygen reduction reaction coupled with the methanol oxidation reaction to construct fuel cells or rechargeable Li-O2 batteries. This Minireview provides a brief overview of recent progress on electrocatalysts based on transition metal nitrides, and outlines the current challenges and future opportunities. PMID:26494184

  13. Pressure-induced phase transitions and metallization in VO2

    NASA Astrophysics Data System (ADS)

    Bai, Ligang; Li, Quan; Corr, Serena A.; Meng, Yue; Park, Changyong; Sinogeikin, Stanislav V.; Ko, Changhyun; Wu, Junqiao; Shen, Guoyin

    2015-03-01

    We report the results of pressure-induced phase transitions and metallization in VO2 based on synchrotron x-ray diffraction, electrical resistivity, and Raman spectroscopy. Our isothermal compression experiments at room temperature and 383 K show that the room temperature monoclinic phase (M 1 ,P 21/c ) and the high-temperature rutile phase (R ,P 42/m n m ) of VO2 undergo phase transitions to a distorted M 1 monoclinic phase (M 1' ,P 21/c ) above 13.0 GPa and to an orthorhombic phase (CaCl2-like, P n n m ) above 13.7 GPa, respectively. Upon further compression, both high-pressure phases transform into a new phase (phase X ) above 34.3 and 38.3 GPa at room temperature and 383 K, respectively. The room temperature M 1 -M 1' phase transition structurally resembles the R -CaCl2 phase transition at 383 K, suggesting a second-order displacive type of transition. Contrary to previous studies, our electrical resistivity results, Raman measurements, as well as ab initio calculations indicate that the new phase X , rather than the M 1' phase, is responsible for the metallization under pressure. The metallization mechanism is discussed based on the proposed crystal structure.

  14. Catalytic mechanism of transition-metal compounds on Mg hydrogen sorption reaction.

    PubMed

    Barkhordarian, Gagik; Klassen, Thomas; Bormann, Rüdiger

    2006-06-01

    The catalytic mechanisms of transition-metal compounds during the hydrogen sorption reaction of magnesium-based hydrides were investigated through relevant experiments. Catalytic activity was found to be influenced by four distinct physico-thermodynamic properties of the transition-metal compound: a high number of structural defects, a low stability of the compound, which however has to be high enough to avoid complete reduction of the transition metal under operating conditions, a high valence state of the transition-metal ion within the compound, and a high affinity of the transition-metal ion to hydrogen. On the basis of these results, further optimization of the selection of catalysts for improving sorption properties of magnesium-based hydrides is possible. In addition, utilization of transition-metal compounds as catalysts for other hydrogen storage materials is considered. PMID:16771356

  15. Antimicrobial Applications of Transition Metal Complexes of Benzothiazole Based Terpolymer: Synthesis, Characterization, and Effect on Bacterial and Fungal Strains

    PubMed Central

    Riswan Ahamed, Mohamed A.; Azarudeen, Raja S.; Kani, N. Mujafar

    2014-01-01

    Terpolymer of 2-amino-6-nitro-benzothiazole-ethylenediamine-formaldehyde (BEF) has been synthesized and characterized by elemental analysis and various spectral techniques like FTIR, UV-Visible, and 1H and 13C-NMR. The terpolymer metal complexes were prepared with Cu2+, Ni2+, and Zn2+ metal ions using BEF terpolymer as a ligand. The complexes have been characterized by elemental analysis and IR, UV-Visible, ESR, 1H-NMR, and 13C-NMR spectral studies. Gel permeation chromatography was used to determine the molecular weight of the ligand. The surface features and crystalline behavior of the ligand and its complexes were analyzed by scanning electron microscope and X-ray diffraction methods. Thermogravimetric analysis was used to analyze the thermal stability of the ligand and its metal complexes. Kinetic parameters such as activation energy (Ea) and order of reaction (n) and thermodynamic parameters, namely, ΔS, ΔF, S*, and Z, were calculated using Freeman-Carroll (FC), Sharp-Wentworth (SW), and Phadnis-Deshpande (PD) methods. Thermal degradation model of the terpolymer and its metal complexes was also proposed using PD method. Biological activities of the ligand and its complexes were tested against Shigella sonnei, Escherichia coli, Klebsiella species, Staphylococcus aureus, Bacillus subtilis, and Salmonella typhimurium bacteria and Aspergillus flavus, Aspergillus niger, Penicillium species, Candida albicans, Cryptococcus neoformans, Mucor species fungi. PMID:25298760

  16. Finding new ternary transition metal selenides and sulphides

    NASA Astrophysics Data System (ADS)

    Narayan, Awadhesh; Bhutani, Ankita; Eckstein, James N.; Shoemaker, Daniel P.; Wagner, Lucas K.

    The transition metal oxides exhibit many interesting physical properties, and have been explored in detail over time. Recently, the transition metal chalchogenides including selenium and sulfur have been of interest because of their correlated electron properties, as seen in the iron based superconductors and the layered transition metal dichalchogenides. However, the chalchogenides are much less explored than the oxides, and there is an open question of whether there may be new materials heretofore undiscovered. We perform a systematic combined theoretical and experimental search over ternary phase diagrams that are empty in the Inorganic Crystal Structure Database containing cations, transition metals, and one of selenium or sulfur. In these 27 ternary systems, we use a probabilistic model to reduce the likelihood of false negative predictions, which results in a list of 24 candidate materials. We then conduct a variety of synthesis experiments to check the candidate materials for stability. While the prediction method did obtain compositions that are stable, none of the candidate materials formed in our experiments. We come to the conclusion that these phase diagrams are either truly empty or have unusual structures or synthesis requirements. This work was supported by the Center for Emergent Superconductivity, Department of Energy Frontier Research Center under Grant No. DEAC0298CH1088.

  17. Epoxy nanocomposites with two-dimensional transition metal dichalcogenide additives.

    PubMed

    Eksik, Osman; Gao, Jian; Shojaee, S Ali; Thomas, Abhay; Chow, Philippe; Bartolucci, Stephen F; Lucca, Don A; Koratkar, Nikhil

    2014-05-27

    Emerging two-dimensional (2D) materials such as transition metal dichalcogenides offer unique and hitherto unavailable opportunities to tailor the mechanical, thermal, electronic, and optical properties of polymer nanocomposites. In this study, we exfoliated bulk molybdenum disulfide (MoS2) into nanoplatelets, which were then dispersed in epoxy polymers at loading fractions of up to 1% by weight. We characterized the tensile and fracture properties of the composite and show that MoS2 nanoplatelets are highly effective at enhancing the mechanical properties of the epoxy at very low nanofiller loading fractions (below 0.2% by weight). Our results show the potential of 2D sheets of transition metal dichalcogenides as reinforcing additives in polymeric composites. Unlike graphene, transition metal dichalcogenides such as MoS2 are high band gap semiconductors and do not impart significant electrical conductivity to the epoxy matrix. For many applications, it is essential to enhance mechanical properties while also maintaining the electrical insulation properties and the high dielectric constant of the polymer material. In such applications, conductive carbon based fillers such as graphene cannot be utilized. This study demonstrates that 2D transition metal dichalcogenide additives offer an elegant solution to such class of problems. PMID:24754702

  18. Synthesis, spectroscopic, cytotoxic aspects and computational study of N-(pyridine-2-ylmethylene)benzo[d]thiazol-2-amine Schiff base and some of its transition metal complexes

    NASA Astrophysics Data System (ADS)

    Abd El-Aziz, Dina M.; Etaiw, Safaa Eldin H.; Ali, Elham A.

    2013-09-01

    N-(pyridine-2-ylmethylene)benzo[d]thiazol-2-amine Schiff base (L) and its Cu(II), Fe(III), Co(II), Ni(II) and Zn(II) complexes were synthesized and characterized by a set of chemical and spectroscopic measurements using elemental analysis, electrical conductance, mass spectra, magnetic susceptibility and spectral techniques (IR, UV-Vis, 1H NMR). Elemental and mass spectrometric data are consistent with the proposed formula. IR spectra confirm the bidentate nature of the Schiff base ligand. The octahedral geometry around Cu(II), Fe(III), Ni(II) and Zn(II) as well as tetrahedral geometry around Co(II) were suggested by UV-Vis spectra and magnetic moment data. The thermal degradation behavior of the Schiff base and its complexes was investigated by thermogravimetric analysis. The structure of the Schiff base and its transition metal complexes was also theoretically studied using molecular mechanics (MM+). The obtained structures were minimized with a semi-empirical (PM3) method. The in vitro antitumor activity of the synthesized compounds was studied. The Zn-complex exhibits significant decrease in surviving fraction of breast carcinoma (MCF 7), liver carcinoma (HEPG2), colon carcinoma (HCT116) and larynx carcinoma (HEP2) cell lines human cancer.

  19. Vibrational scaling factors for transition metal carbonyls

    NASA Astrophysics Data System (ADS)

    Assefa, M. K.; Devera, J. L.; Brathwaite, A. D.; Mosley, J. D.; Duncan, M. A.

    2015-11-01

    Vibrational frequencies for a selected set of transition metal carbonyl complexes are computed with various forms of density functional theory (B3LYP, BP86, M06, and M06-L), employing several different basis sets. The computed frequencies for the carbonyl stretches are compared to the experimental values obtained from gas phase infrared spectra of isolated neutrals and ions. Recommended carbonyl-stretch scaling factors which are developed vary significantly for different functionals, but there is little variation with basis set. Scaled frequencies compared to experimental spectra for cobalt and tantalum carbonyl cations reveal additional variations in multiplet patterns and relative band intensities for different functionals.

  20. Strain induced fragility transition in metallic glass

    PubMed Central

    Yu, Hai-Bin; Richert, Ranko; Maaß, Robert; Samwer, Konrad

    2015-01-01

    Relaxation dynamics are the central topic in glassy physics. Recently, there is an emerging view that mechanical strain plays a similar role as temperature in altering the relaxation dynamics. Here, we report that mechanical strain in a model metallic glass modulates the relaxation dynamics in unexpected ways. We find that a large strain amplitude makes a fragile liquid become stronger, reduces dynamical heterogeneity at the glass transition and broadens the loss spectra asymmetrically, in addition to speeding up the relaxation dynamics. These findings demonstrate the distinctive roles of strain compared with temperature on the relaxation dynamics and indicate that dynamical heterogeneity inherently relates to the fragility of glass-forming materials. PMID:25981888

  1. Electrical Conduction in Transition-Metal Salts

    NASA Astrophysics Data System (ADS)

    Grado-Caffaro, M. A.; Grado-Caffaro, M.

    2016-04-01

    We predict that a given transition-metal salt as, for example, a K2CuCl4·2H2O-type compound, can behave as an electrical conductor in the paramagnetic case. In fact, we determine the electrical conductance in a salt of this type. This conductance is found to be quantised in agreement with previous well-known results. Related mathematical expressions in the context of superexchange interaction are obtained. In addition, we determine the corresponding (macroscopically viewed) current density and the associated electron wave functions.

  2. Strain Engineering of Transition Metal Dichalcogenides

    NASA Astrophysics Data System (ADS)

    Dadgar, Ali; Pasupathy, Abhay; Herman, Irving; Wang, Dennis; Kang, Kyungnam; Yang, Eui-Hyeok

    The application of strain to materials can cause changes to bandwidth, effective masses, degeneracies and even structural phases. In the case of the transition metal dichalcogenide (TMD) semiconductors, small strain (around 1 percent) is expected to change band gaps and mobilities, while larger strains are expected to cause phase changes from the triangular 2H phase to orthorhombic 1T' phases. We will describe experimental techniques to apply small and large (around 10 percent) strains to one or few layer samples of the TMD semiconductors, and describe the effect of the strain using optical (Raman, photoluminescence) and cryogenic transport techniques.

  3. Electrocatalysis using transition metal carbide and oxide nanocrystals

    NASA Astrophysics Data System (ADS)

    Regmi, Yagya N.

    Carbides are one of the several families of transition metal compounds that are considered economic alternatives to catalysts based on noble metals and their compounds. Phase pure transition metal carbides of group 4-6 metals, in the first three periods, were synthesized using a common eutectic salt flux synthesis method, and their electrocatalytic activities compared under uniform electrochemical conditions. Mo2C showed highest hydrogen evolution reaction (HER) and oxygen reduction reaction (ORR) activities among the nine metal carbides investigated, but all other metal carbides also showed substantial activities. All the metal carbides showed remarkable enhancement in catalytic activities as supports, when compared to traditional graphitic carbon as platinum support. Mo2C, the most active transition metal carbide electrocatalyst, was prepared using four different synthesis routes, and the synthesis route dependent activities compared. Bifunctional Mo 2C that is HER as well as oxygen evolution reaction (OER) active, was achieved when the carbide was templated on a multiwalled carbon nanotube using carbothermic reduction method. Bimetallic carbides of Fe, Co, and Ni with Mo or W were prepared using a common carbothermic reduction method. Two different stoichiometries of bimetallic carbides were obtained for each system within a 60 °C temperature window. While the bimetallic carbides showed relatively lower electrocatalytic activities towards HER and ORR in comparison to Mo2C and WC, they revealed remarkably higher OER activities than IrO2 and RuO2, the state-of-the-art OER catalysts. Bimetallic oxides of Fe, Co, and Ni with Mo and W were also prepared using a hydrothermal synthesis method and they also revealed OER activities that are much higher than RuO2 and IrO2. Additionally, the OER activities were dependent on the degree and nature of hydration in the bimetallic oxide crystal lattice, with the completely hydrated, as synthesized, cobalt molybdate and nickel

  4. Vinyl polymer agglomerate based transition metal cation chelating ion-exchange resin containing the 8-hydroxyquinoline functional group

    SciTech Connect

    Landing, W.M.; Haraldsson, C.; Paxeus, N.

    1986-12-01

    A simple synthetic route has been developed for the immobilization of 8-hydroxyquinoline onto Fractogel TSK, a highly porous, mechanically and chemically stable, hydrophilic organic resin gel. The product exhibits an exchange capacity comparable to the highest values reported for silica-immobilized 8-hydroxyquinoline but is more stable at high pH. The resin's selectivity and efficiency of collection of cationic metal species from freshwater and seawater were investigated. The resin was used in a column sequence to obtain concentration and speciation data for Al, Mn, Fe, Co, Cu, Zn, and Cd in an organic-rich freshwater sample.

  5. Transition-Metal-Catalyzed Bioorthogonal Cycloaddition Reactions.

    PubMed

    Yang, Maiyun; Yang, Yi; Chen, Peng R

    2016-02-01

    In recent years, bioorthogonal reactions have emerged as a powerful toolbox for specific labeling and visualization of biomolecules, even within the highly complex and fragile living systems. Among them, copper(I)-catalyzed azide-alkyne cycloaddition (CuAAC) reaction is one of the most widely studied and used biocompatible reactions. The cytotoxicity of Cu(I) ions has been greatly reduced due to the use of Cu(I) ligands, which enabled the CuAAC reaction to proceed on the cell surface, as well as within an intracellular environment. Meanwhile, other transition metals such as ruthenium, rhodium and silver are now under development as alternative sources for catalyzing bioorthogonal cycloadditions. In this review, we summarize the development of CuAAC reaction as a prominent bioorthogonal reaction, discuss various ligands used in reducing Cu(I) toxicity while promoting the reaction rate, and illustrate some of its important biological applications. The development of additional transition metals in catalyzing cycloaddition reactions will also be briefly introduced. PMID:27572985

  6. Metal Insulator transition in Vanadium Dioxide

    NASA Astrophysics Data System (ADS)

    Jovaini, Azita; Fujita, Shigeji; Suzuki, Akira; Godoy, Salvador

    2012-02-01

    MAR12-2011-000262 Abstract Submitted for the MAR12 Meeting of The American Physical Society Sorting Category: 03.9 (T) On the metal-insulator-transition in vanadium dioxide AZITA JOVAINI, SHIGEJI FUJITA, University at Buffalo, SALVADOR GODOY, UNAM, AKIRA SUZUKI, Tokyo University of Science --- Vanadium dioxide (VO2) undergoes a metal-insulator transition (MIT) at 340 K with the structural change from tetragonal to monoclinic crystal. The conductivity _/ drops at MIT by four orders of magnitude. The low temperature monoclinic phase is known to have a lower ground-state energy. The existence of the k-vector k is prerequisite for the conduction since the k appears in the semiclassical equation of motion for the conduction electron (wave packet). The tetragonal (VO2)3 unit is periodic along the crystal's x-, y-, and z-axes, and hence there is a three-dimensional k-vector. There is a one-dimensional k for a monoclinic crystal. We believe this difference in the dimensionality of the k-vector is the cause of the conductivity drop. Prefer Oral Session X Prefer .

  7. Laser Assisted Additively Manufactured Transition Metal Coating on Aluminum

    NASA Astrophysics Data System (ADS)

    Vora, Hitesh D.; Rajamure, Ravi Shanker; Roy, Anurag; Srinivasan, S. G.; Sundararajan, G.; Banerjee, Rajarshi; Dahotre, Narendra B.

    2016-07-01

    Various physical and chemical properties of surface and subsurface regions of Al can be improved by the formation of transition metal intermetallic phases (Al x TM y ) via coating of the transition metal (TM). The lower equilibrium solid solubility of TM in Al (<1 at.%) is a steep barrier to the formation of solid solutions using conventional alloying methods. In contrast, as demonstrated in the present work, surface engineering via a laser-aided additive manufacturing approach can effectively synthesize TM intermetallic coatings on the surface of Al. The focus of the present work included the development of process control to achieve thermodynamic and kinetic conditions necessary for desirable physical, microstructural and compositional attributes. A multiphysics finite element model was developed to predict the temperature profile, cooling rate, melt depth, dilution of W in Al matrix and corresponding micro-hardness in the coating, and the interface between the coating and the base material and the base material.

  8. Laser Assisted Additively Manufactured Transition Metal Coating on Aluminum

    NASA Astrophysics Data System (ADS)

    Vora, Hitesh D.; Rajamure, Ravi Shanker; Roy, Anurag; Srinivasan, S. G.; Sundararajan, G.; Banerjee, Rajarshi; Dahotre, Narendra B.

    2016-05-01

    Various physical and chemical properties of surface and subsurface regions of Al can be improved by the formation of transition metal intermetallic phases (Al x TM y ) via coating of the transition metal (TM). The lower equilibrium solid solubility of TM in Al (<1 at.%) is a steep barrier to the formation of solid solutions using conventional alloying methods. In contrast, as demonstrated in the present work, surface engineering via a laser-aided additive manufacturing approach can effectively synthesize TM intermetallic coatings on the surface of Al. The focus of the present work included the development of process control to achieve thermodynamic and kinetic conditions necessary for desirable physical, microstructural and compositional attributes. A multiphysics finite element model was developed to predict the temperature profile, cooling rate, melt depth, dilution of W in Al matrix and corresponding micro-hardness in the coating, and the interface between the coating and the base material and the base material.

  9. High-Pressure Thermodynamic Properties of f-electron Metals, Transition Metal Oxides, and Half-Metallic Magnets

    SciTech Connect

    Scalettar, Richard T.; Pickett, Warren E.

    2004-07-01

    This project involves research into the thermodynamic properties of f-electron metals, transition metal oxides, and half-metallic magnets at high pressure. These materials are ones in which the changing importance of electron-electron interactions as the distance between atoms is varied can tune the system through phase transitions from localized to delocalized electrons, from screened to unscreened magnetic moments, and from normal metal to one in which only a single spin specie can conduct. Three main thrusts are being pursued: (1) Mott transitions in transition metal oxides, (2) magnetism in half-metallic compounds, and (3) large volume-collapse transitions in f-band metals.

  10. High-Pressure Thermodynamic Properties of f-electron Metals, Transition Metal Oxides, and Half-Metallic Magnets

    SciTech Connect

    Richard T. Scalettar; Warren E. Pickett

    2005-08-02

    This project involves research into the thermodynamic properties of f-electron metals, transition metal oxides, and half-metallic magnets at high pressure. These materials are ones in which the changing importance of electron-electron interactions as the distance between atoms is varied can tune the system through phase transitions from localized to delocalized electrons, from screened to unscreened magnetic moments, and from normal metal to one in which only a single spin specie can conduct. Three main thrusts are being pursued: (i) Mott transitions in transition metal oxides, (ii) magnetism in half-metallic compounds, and (iii) large volume-collapse transitions in f-band metals.

  11. Research progress on polyoxometalate-based transition-metal-rare-earth heterometallic derived materials: synthetic strategies, structural overview and functional applications.

    PubMed

    Zhao, Jun-Wei; Li, Yan-Zhou; Chen, Li-Juan; Yang, Guo-Yu

    2016-03-15

    With the rapid development of science and technology and the trend of multidisciplinary pervasion, POM-based TM-RE heterometallic chemistry (POM = polyoxometalate, TM = transition-metal, RE = rare-earth) has become one of the most rapidly growing and challengeable areas of inorganic chemistry due to the impressive structural diversities, various chemical compositions and potential applications of these materials in magnetism, optics, electrochemistry, electrocatalysis and materials science. Over the past several years, continuous interest and persisting efforts have been dedicated to the preparation and exploration of POM-based TM-RE heterometallic derived materials (PTRHDMs), which have led to more than two hundred PTRHDMs. In this review, we summarize the structural types of reported PTRHDMs together with synthetic strategies, structural motifs and relevant functional applications. The exciting array of this emerging research theme presages continuous growth and great vitality. In the last section, some prospects of this branch are also presented and possible guidance for future work is outlined. PMID:26894638

  12. Synthesis, spectral characterization, molecular modeling, thermal study and biological evaluation of transition metal complexes of a bidentate Schiff base ligand

    NASA Astrophysics Data System (ADS)

    Chandra, Sulekh; Bargujar, Savita; Nirwal, Rita; Qanungo, Kushal; Sharma, Saroj K.

    2013-09-01

    Complexes of copper(II) and nickel(II) of general composition M(L)2X2, have been synthesized [where L = 3-Bromoacetophenone thiosemicarbazone and X = CH3COO-, Cl- and NO3-]. All the complexes were characterized by elemental analysis, magnetic moments, IR, electronic and EPR spectral studies. The ligand behaved as bidentate and coordinated through sulfur of sbnd Cdbnd S group and nitrogen atoms of sbnd Cdbnd N group. The copper(II) and nickel(II) complexes were found to have magnetic moments 1.94-2.02 BM, 2.96-3.02 BM respectively which was corresponding to one and two unpaired electrons respectively. The molar conductance of the complexes in solution of DMSO lies in the range of 10-20 Ω-1 cm2 mol-1 indicating their non-electrolytic behavior. On the basis of EPR, electronic and infrared spectral studies, tetragonal geometry has been assigned for copper(II) complexes and an octahedral geometry for nickel(II) complexes. The values of Nephelauxetic parameter β lie in the range 0.19-0.37 which indicated the covalent character in metal ligand ‘σ' bond. Synthesized ligand and its copper(II) and nickel(II) complexes have also been screened against different bacterial and fungal species which suggested that complexes are more active than the ligands in antimicrobial activities.

  13. New Layered Ternary Transition-Metal Tellurides

    NASA Astrophysics Data System (ADS)

    Mar, Arthur

    Several new ternary transition-metal tellurides, a class of compounds hitherto largely unexplored, have been synthesized and characterized. These are layered materials whose structures have been determined by single -crystal X-ray diffraction methods. The successful preparation of the compound TaPtTe_5 was crucial in developing an understanding of the MM'Te_5 (M = Nb, Ta; M' = Ni, Pd, Pt) series of compounds, which adopt either of two possible closely-related layered structures. Interestingly, the compound TaPdTe _5 remains unknown. Instead, the compound Ta_4Pd_3Te _{16} has been prepared. Its structure is closely related to that of the previously prepared compound Ta_3Pd _3Te_{14}. The physical properties of these compounds have been measured and correlated with the metal substitutions and interlayer separations. A new series of compounds, MM'Te _4 (M = Nb, Ta; M' = Ru, Os, Rh, Ir), has been discovered. The structure of NbIrTe_4 serves as a prototype: it is an ordered variant of the binary telluride WTe_2. Electronic band-structure calculations have been performed in order to rationalize the trends in metal-metal and tellurium -tellurium bonding observed in WTe_2 and the MM'Te_4 phases. Extension of these studies to include main-group metals has resulted in the synthesis of the new layered ternary germanium tellurides TiGeTe_6, ZrGeTe_4 , and HfGeTe_4. Because germanium can behave ambiguously in its role as a metalloid element, it serves as an anion by capping the metal-centered trigonal prisms and also as a cation in being coordinated in turn by other tellurium atoms in a trigonal pyramidal fashion. Structural relationships among these compounds are illustrated through the use of bicapped trigonal prisms and trigonal pyramids as the basic structural building blocks. The electrical and magnetic properties of these compounds have been measured. Insight into the unusual bonding and physical properties of these germanium-containing compounds has been gained through

  14. Synthesis, solvatochromaticity and bioactivities of some transition metal complexes with 2-(R-benzylideneamino)-pyridin-3-ol Schiff base derivatives

    NASA Astrophysics Data System (ADS)

    Ahmed, I. S.; Kassem, M. A.

    2010-10-01

    New four Schiff bases are prepared by condensation of 2-amino-pyridin-3-ol with 3, 4-dihydroxy-benzaldehyde (I), 2-hydroxybenzaldehyde (II), 5-bromo-2-hydroxybenzaldehyde (III), and 4-dimethylaminobenzaldehyde (IV). The structures of these compounds are characterized based on elemental analyses (C. H. N), IR and 1H NMR. Also, the electronic absorption spectra are recorded in organic solvents of different polarity. The solvents are selected to be covered a wide range of parameters (refractive index, dielectric constant and hydrogen bonding capacity). The UV-vis absorption spectra of Schiff base compounds are investigated in aqueous buffer solutions of varying pH and utilized for the determination of ionization constant, p Ka and activation free energy, Δ G* of the ionization process. The biological activity against bacterial species and fungi as microorganisms representing different microbial categories such as (two Gram-negative bacteria, Eschericha coli and Agrobacterium sp.),three Gram-positive bacteria ( Staphylococcus aureus, Bacillus subtlus and Bacillus megatherium), yeast ( Candida albicans), and fungi ( Aspergillus niger) were studied.

  15. Smoothing of ultrathin silver films by transition metal seeding

    NASA Astrophysics Data System (ADS)

    Anders, André; Byon, Eungsun; Kim, Dong-Ho; Fukuda, Kentaro; Lim, Sunnie H. N.

    2006-11-01

    The nucleation and coalescence of silver islands on coated glass was investigated by in situ measurements of the sheet resistance. Sub-monolayer amounts of niobium and other transition metals were deposited prior to the deposition of silver. It was found that in some cases, the transition metals lead to coalescence of silver at nominally thinner films with smoother topology. The smoothing or roughening effects by the presence of the transition metal can be explained by kinetically limited transition metal islands growth and oxidation, followed by defect-dominated nucleation of silver.

  16. Electron Topological Transitions of 31/2 Kind in Metals

    NASA Astrophysics Data System (ADS)

    Mikitik, G. P.; Sharlai, Yu. V.

    2016-06-01

    We consider electron topological transitions associated with certain points of band-contact lines in metals. These transitions are 31/2 kind according to the classification of Lifshits and are widespread in metals with inversion symmetry and a weak spin-orbit interaction. The 31/2 -order transitions can be detected with the magnetic susceptibility. As an example, we consider these transitions in graphite.

  17. Engineering skyrmions in transition-metal multilayers for spintronics

    NASA Astrophysics Data System (ADS)

    Dupé, B.; Bihlmayer, G.; Böttcher, M.; Blügel, S.; Heinze, S.

    2016-06-01

    Magnetic skyrmions are localized, topologically protected spin structures that have been proposed for storing or processing information due to their intriguing dynamical and transport properties. Important in terms of applications is the recent discovery of interface stabilized skyrmions as evidenced in ultra-thin transition-metal films. However, so far only skyrmions at interfaces with a single atomic layer of a magnetic material were reported, which greatly limits their potential for application in devices. Here we predict the emergence of skyrmions in [4d/Fe2/5d]n multilayers, that is, structures composed of Fe biatomic layers sandwiched between 4d and 5d transition-metal layers. In these composite structures, the exchange and the Dzyaloshinskii-Moriya interactions that control skyrmion formation can be tuned separately by the two interfaces. This allows engineering skyrmions as shown based on density functional theory and spin dynamics simulations.

  18. Engineering skyrmions in transition-metal multilayers for spintronics.

    PubMed

    Dupé, B; Bihlmayer, G; Böttcher, M; Blügel, S; Heinze, S

    2016-01-01

    Magnetic skyrmions are localized, topologically protected spin structures that have been proposed for storing or processing information due to their intriguing dynamical and transport properties. Important in terms of applications is the recent discovery of interface stabilized skyrmions as evidenced in ultra-thin transition-metal films. However, so far only skyrmions at interfaces with a single atomic layer of a magnetic material were reported, which greatly limits their potential for application in devices. Here we predict the emergence of skyrmions in [4d/Fe2/5d]n multilayers, that is, structures composed of Fe biatomic layers sandwiched between 4d and 5d transition-metal layers. In these composite structures, the exchange and the Dzyaloshinskii-Moriya interactions that control skyrmion formation can be tuned separately by the two interfaces. This allows engineering skyrmions as shown based on density functional theory and spin dynamics simulations. PMID:27257020

  19. Engineering skyrmions in transition-metal multilayers for spintronics

    PubMed Central

    Dupé, B.; Bihlmayer, G.; Böttcher, M.; Blügel, S.; Heinze, S.

    2016-01-01

    Magnetic skyrmions are localized, topologically protected spin structures that have been proposed for storing or processing information due to their intriguing dynamical and transport properties. Important in terms of applications is the recent discovery of interface stabilized skyrmions as evidenced in ultra-thin transition-metal films. However, so far only skyrmions at interfaces with a single atomic layer of a magnetic material were reported, which greatly limits their potential for application in devices. Here we predict the emergence of skyrmions in [4d/Fe2/5d]n multilayers, that is, structures composed of Fe biatomic layers sandwiched between 4d and 5d transition-metal layers. In these composite structures, the exchange and the Dzyaloshinskii–Moriya interactions that control skyrmion formation can be tuned separately by the two interfaces. This allows engineering skyrmions as shown based on density functional theory and spin dynamics simulations. PMID:27257020

  20. Tailoring magnetic skyrmions in ultra-thin transition metal films.

    PubMed

    Dupé, Bertrand; Hoffmann, Markus; Paillard, Charles; Heinze, Stefan

    2014-01-01

    Skyrmions in magnetic materials offer attractive perspectives for future spintronic applications since they are topologically stabilized spin structures on the nanometre scale, which can be manipulated with electric current densities that are by orders of magnitude lower than those required for moving domain walls. So far, they were restricted to bulk magnets with a particular chiral crystal symmetry greatly limiting the number of available systems and the adjustability of their properties. Recently, it has been experimentally discovered that magnetic skyrmion phases can also occur in ultra-thin transition metal films at surfaces. Here we present an understanding of skyrmions in such systems based on first-principles electronic structure theory. We demonstrate that the properties of magnetic skyrmions at transition metal interfaces such as their diameter and their stability can be tuned by the structure and composition of the interface and that a description beyond a micromagnetic model is required in such systems. PMID:24893652

  1. Radiation damage of transition metal carbides

    SciTech Connect

    Dixon, G.

    1991-01-01

    In this grant period we have investigated electrical properties of transition metal carbides and radiation-induced defects produced by low-temperature electron irradiation in them. Special attention has been given to the composition VC[sub 0.88] in which the vacancies on the carbon sublattice of this fcc crystal order to produce a V[sub 8]C[sub 7] superlattice. The existence of this superlattice structure was found to make the crystal somewhat resistant to radiation damage at low doses and/or at ambient temperature. At larger doses significant changes in the resistivity are produced. Annealing effects were observed which we believe to be connected with the reconstitution of the superlattice structure.

  2. Excited Biexcitons in Transition Metal Dichalcogenides

    NASA Astrophysics Data System (ADS)

    Zhang, David

    Recently, experimental measurements and theoretical modeling have been in a disagreement concerning the binding energy of biexctions in transition metal dichalcogenides. While theory predicts a smaller binding energy (~20 meV) that is, as logically expected, lower than that of the trion, experiment finds values much larger (~60 meV), actually exceeding those for the trion. In this work, we show that there exists an excited state of the biexciton which yields binding energies that match well with experimental findings and thus gives a plausible explanation for the apparent discrepancy. Furthermore, it is shown that the electron-hole correlation functions of the ground state biexciton and trion are remarkably similar, possibly explaining why a distinct signature of ground state biexcitons would not have been noticed experimentally.

  3. Trion dynamics in Transition Metal Dichalcogenide Monolayers

    NASA Astrophysics Data System (ADS)

    Singh, Akshay; Tran, Kha; Wu, Sanweng; Ross, Jason; Moody, Galan; Xu, Xiaodong; Li, Elaine

    2015-03-01

    Transition Metal Dichalcogenides (TMD's) in the monolayer limit, exhibit interesting phenomena including increased photoluminescence, spin-valley coupling and many-body effects. Excitons (bound electron-hole pairs) and trions (charged excitons) in these materials have unusually large binding energy and dominate the optical response near the band gap. In particular, trions can drift under application of an electric field and have higher spin lifetimes increasing applications in quantum spin models. We study the temporal dynamics of excitons and trions including their formation and lifetimes using time resolved two-color pump-probe spectroscopy on a monolayer TMD (MoSe2). Trions are observed to have vastly different temporal dynamics with much slower decay than excitons. We also observe rapid formation of trions when resonantly pumped while a slow rise (in temporal response) is seen for other excitation energies. We suggest that localization of trions needs to be taken into account to explain these observations.

  4. Excited Biexcitons in Transition Metal Dichalcogenides.

    PubMed

    Zhang, David K; Kidd, Daniel W; Varga, Kálmán

    2015-10-14

    The Stochastic Variational Method (SVM) is used to show that the effective mass model correctly estimates the binding energies of excitons and trions but fails to predict the experimental binding energy of the biexciton. Using high-accuracy variational calculations, it is demonstrated that the biexciton binding energy in transition metal dichalcogenides is smaller than the trion binding energy, contradicting experimental findings. It is also shown that the biexciton has bound excited states and that the binding energy of the L = 0 excited state is in very good agreement with experimental data. This excited state corresponds to a hole attached to a negative trion and may be a possible resolution of the discrepancy between theory and experiment. PMID:26422057

  5. Energy bands in some transition metals

    NASA Astrophysics Data System (ADS)

    Laurent, D. G.

    1981-08-01

    Self consistent linear combination of Gaussian orbitals energy band calculations were performed for the two paramagnetic 3d transition metals, chromium and vanadium. The energy bands densities of states and Fermi surfaces were obtained using the two most popular local exchange correlation potentials (Kohn-Sham-Gaspar and von Barth-Hedin) for chromium and the Kohn-Sham-Gaspar potential alone for vanadium. A comparison was made with the available experimental data. New interpretations for some of the neutron scattering data are made in the chromium case. Results are also presented for the Compton profiles and optical conductivities. These correlate well with the experiments if appropriate angular averages (for the Compton profile) and lifetime effcts (for the optical conductivity) are included. The electron energy loss spectrum, computed over the range 0-6.5 eV agreed well with experiment.

  6. Main-group elements as transition metals.

    PubMed

    Power, Philip P

    2010-01-14

    The last quarter of the twentieth century and the beginning decade of the twenty-first witnessed spectacular discoveries in the chemistry of the heavier main-group elements. The new compounds that were synthesized highlighted the fundamental differences between their electronic properties and those of the lighter elements to a degree that was not previously apparent. This has led to new structural and bonding insights as well as a gradually increasing realization that the chemistry of the heavier main-group elements more resembles that of transition-metal complexes than that of their lighter main-group congeners. The similarity is underlined by recent work, which has shown that many of the new compounds react with small molecules such as H(2), NH(3), C(2)H(4) or CO under mild conditions and display potential for applications in catalysis. PMID:20075912

  7. Spin-orbit damping in transition metals

    NASA Astrophysics Data System (ADS)

    Gilmore, Keith

    2008-03-01

    Magnetization dynamics are routinely described with the Landau-Lifshitz-Gilbert (LLG) equation. However, it is expected that the LLG equation fails to properly describe the large amplitude dynamics that occur during magnetization reversal. Improving switching speeds in nanoscale devices by tailoring materials requires both a qualitative understanding of the relaxation processes that contribute to damping and the ability to quantitatively calculate the resulting damping rates. We consider small amplitude LLG damping in transition metals as a prelude to approaching the more complicated mechanisms expected in complete reversal events. LLG damping rates in pure transition metal systems have non-monotonic temperature dependencies that have been empirically shown by Heinrich et al. [1] to have one part proportional to the conductivity and one part proportional to the resistivity. Kambersky [2] postulated that both contributions result from a torque between the spin and orbital moments. We have conducted first-principles calculations that validate this claim for single element systems [3]. Our calculations for Fe, Co, and Ni both qualitatively match the two trends observed in measurements and quantitatively agree with the observed damping rates. We will discuss how the spin-orbit interaction produces two contributions to damping with nearly opposite temperature dependencies and compare calculations of the damping rate versus resistivity with experimental results. [1] B. Heinrich, D.J. Meredith, and J.F. Cochran, J. Appl. Phys., 50(11), 7726 (1979). [2] V. Kambersky, Czech. J. Phys. B, 26, 1366 (1976). [3] K. Gilmore, Y.U. Idzerda, and M.D. Stiles, Phys. Rev. Lett., 99, 027204 (2007).

  8. Generic trend of work functions in transition-metal carbides and nitrides

    SciTech Connect

    Yoshitake, Michiko

    2014-11-15

    Transition-metal carbides and nitrides (TMCs and TMNs) are promising electrode materials for various electronic devices such as metal-oxide-semiconductor field-effect transistors and metal-insulator-metal capacitors. In this paper, the work functions of TMCs and TMNs are discussed systematically. Based upon the origin of the work function, the effect upon transition metal species by different periodic table groups is explained, carbides are compared with nitrides for the same transition metal, and the effect of carbon or nitrogen vacancies is discussed. In addition, a method to estimate the generic trend of the work function is proposed for TMC{sub x}, TMN{sub x}, TMC{sub 1−y}N{sub y} (transition metal carbonitrides), and TM{sub 1−z}TM′{sub z}C (alloy carbides)

  9. New Gallides and Germanides of Transition Metals

    NASA Astrophysics Data System (ADS)

    Popova, S. V.

    1982-01-01

    The analysis of the average atomic volumes (AAV) of the intermediate phases from the concentration was done in many two-component systems. It was shown that in some systems (namely transition metal with non-transition element from the IIIrd or IVth group of the periodic table) the AAV of the intermediate phases are much more less than the sum of the volumes of the pure components. It means that the formation of the intermediate phases in such systems is accompanied by a rather large decreasing of the volume in comparison with the mixture of elements. For this reason the high pressure conditions are favourable for the formation of the intermediate phases in such systems from the thermodynamical point of view. On the ground of these data the systems W-Ga, W-Ge, Re-Ga, Os-Ga, Sc-Ga, Ta-Ga, were investigated at high pressures and temperatures. It was found that many new phases are crystallised in these systems. All of them are metastable at room pressure. The composition and crystal structures of these phases were investigated at ordinary conditions.

  10. Soldering of Carbon Materials Using Transition Metal Rich Alloys.

    PubMed

    Burda, Marek; Lekawa-Raus, Agnieszka; Gruszczyk, Andrzej; Koziol, Krzysztof K K

    2015-08-25

    Joining of carbon materials via soldering has not been possible up to now due to lack of wetting of carbons by metals at standard soldering temperatures. This issue has been a severely restricting factor for many potential electrical/electronic and mechanical applications of nanostructured and conventional carbon materials. Here we demonstrate the formation of alloys that enable soldering of these structures. By addition of several percent (2.5-5%) of transition metal such as chromium or nickel to a standard lead-free soldering tin based alloy we obtained a solder that can be applied using a commercial soldering iron at typical soldering temperatures of approximately 350 °C and at ambient conditions. The use of this solder enables the formation of mechanically strong and electrically conductive joints between carbon materials and, when supported by a simple two-step technique, can successfully bond carbon structures to any metal terminal. It has been shown using optical and scanning electron microscope images as well as X-ray diffraction patterns and energy dispersive X-ray mapping that the successful formation of carbon-solder bonds is possible, first, thanks to the uniform nonreactive dispersion of transition metals in the tin-based matrix. Further, during the soldering process, these free elements diffuse into the carbon-alloy border with no formation of brazing-like carbides, which would damage the surface of the carbon materials. PMID:26256042

  11. Metal-Insulator Transition and Superconductivity in the Two-Orbital Hubbard-Holstein Model for Iron-Based Superconductors

    NASA Astrophysics Data System (ADS)

    Yamada, Takemi; Ishizuka, Jun; Ōno, Yoshiaki

    2014-04-01

    We investigate a two-orbital model for iron-based superconductors to elucidate the effect of interplay between electron correlation and Jahn-Teller electron-phonon coupling by using the dynamical mean-field theory combined with the exact diagonalization method. When the intra- and inter-orbital Coulomb interactions, U and U', increase with U = U', both the local spin and orbital susceptibilities, χs and χo, increase with χs = χo in the absence of the Hund’s rule coupling J and the electron-phonon coupling g. In the presence of J and g, there are distinct two regimes: for J ≳ 2g2/ω 0 with the phonon frequency ω0, χs is enhanced relative to χo and shows a divergence at J = Jc above which the system becomes Mott insulator, while for J ≲ 2g2/ω 0, χo is enhanced relative to χs and shows a divergence at g = gc above which the system becomes bipolaronic insulator. In the former regime, the superconductivity is mediated by antiferromagnetic fluctuations enhanced due to Fermi-surface nesting and is found to be largely dependent on carrier doping. On the other hand, in the latter regime, the superconductivity is mediated by ferro-orbital fluctuations and is observed for wide doping region including heavily doped case without the Fermi-surface nesting.

  12. Development of hybrid materials based on sponge supported reduced graphene oxide and transition metal hydroxides for hybrid energy storage devices

    PubMed Central

    Dubal, Deepak P.; Holze, Rudolf; Gomez-Romero, Pedro

    2014-01-01

    Earnest efforts have been taken to design hybrid energy storage devices using hybrid electrodes based on capacitive (rGO) and pseudocapacitive (Ni(OH)2 and Co(OH)2) materials deposited on the skeleton of 3D macroporous (indicate sponge material) sponge support. Conducting framework was formed by coating rGO on macroporous sponge on which subsequent deposition of Ni(OH)2 and Co(OH)2 was carried out. The synergetic combination of rGO and Ni(OH)2 or Co(OH)2) provides dual charge-storing mechanisms whereas 3D framework of sponge allows excellent accessibility of electrolyte to hybrid electrodes. Moreover, to further increase the energy density, hybrid devices have been fabricated with SP@rGO@Ni or SP@rGO@Co and SP@rGO as positive and negative electrodes, respectively. These hybrid devices operate with extended operating voltage windows and achieve remarkable electrochemical supercapacitive properties which make them truly promising energy storage devices for commercial production. PMID:25483007

  13. Structural, magnetic, and redox diversity of first-row transition metal complexes of a pyridine-based macrocycle: well-marked trends supported by theoretical DFT calculations.

    PubMed

    Drahoš, Bohuslav; Herchel, Radovan; Trávníček, Zdeněk

    2015-04-01

    A series of first-row transition metal complexes with 15-membered pyridine-based macrocycle (3,12,18-triaza-6,9-dioxabicyclo[12.3.1]octadeca-1(18),14,16-triene = L) was prepared ([M(II)(L)Cl2], where M = Mn, Co, Ni, Zn (1, 3, 4, 6); [Fe(III)(L)Cl2]Cl (2), [Cu(II)(L)Cl]Cl (5)) and thoroughly characterized. Depending on the complexated metal atom, the coordination number varies from 7 (Mn, Fe, Co), through 5 + 2 for Ni and 4 + 1 for Cu, to 5 for Zn accompanied by changes in the coordination geometry from the pentagonal bipyramid (1-4) to the square pyramid (5 and 6). Along the series, the metal-oxygen distances were prolonged in such manner that their bonding character was investigated, apart from X-ray structural analysis, also by ab initio calculations (Mayer's bond order, electron localization function), which confirmed that, in 4 and 5, two and one oxygen donor atoms are semicoordinated, respectively, and one and two oxygen atoms are uncoordinated in 5, and 6, respectively. On the basis of the temperature variable magnetic susceptibility measurements, 1 and 2 behave as expected for 3d(5) high-spin configuration with negligible zero-field splitting (ZFS). On the other hand, a large axial ZFS (D(Co) ≈ 40 cm(-1), D(Ni) ≈ -6.0 cm(-1)) was found for 3 and 4, and rhombic ZFS (E/D ≈ 0.15) for 4. Antiferromagnetic exchange coupling was observed for 4 and 5 (J(Ni) = -0.48 cm(-1), and J(Cu) = -2.43 cm(-1), respectively). The obtained results correlate well with ab initio calculations of ZFS parameters as well as J-values, which indicate that the antiferromagnetic exchange is mediated by hydrogen bonds. The complexes were also investigated by cyclic voltammetry in water or acetonitrile. A quasi-reversible couple Mn(II)/Mn(III) at 1.13/0.97 V, an almost reversible couple Fe(II)/Fe(III) at 0.51/0.25 V, and a one-step/multistep reduction/oxidation of Cu(II) complex 5 at -0.33 V/0.06-0.61 V were detected. PMID:25761063

  14. Polytypism in superhard transition-metal triborides

    PubMed Central

    Liang, Yongcheng; Yang, Jiong; Yuan, Xun; Qiu, Wujie; Zhong, Zheng; Yang, Jihui; Zhang, Wenqing

    2014-01-01

    The quest of novel compounds with special structures and unusual functionalities continues to be a central challenge to modern materials science. Even though their exact structures have puzzled scientists for decades, superhard transition-metal borides (TMBs) have long been believed to exist only in simple crystal structures. Here, we report on a polytypic phenomenon in superhard WB3 and MoB3 with a series of energetically degenerate structures due to the random stacking of metal layers amongst the interlocking boron layers. Such polytypism can create a multiphase solid-solution compound with a large number of interfaces amongst different polytypes, and these interfaces will strongly hinder the interlayer sliding movement within each polytype, thereby further increase the hardness of this particular material. Furthermore, in contrast to the conventional knowledge that intrinsically strong chemical bonds in superhard materials should lead to high lattice thermal conductivity, the polytypic TMB3 manifest anomalously low lattice thermal conductivity due to structural disorders and phonon folding. These findings promise to open a new avenue to searching for novel superhard materials with additional functionalities. PMID:24863493

  15. M5Si3(M=Ti, Nb, Mo) Based Transition-Metal Silicides for High Temperature Applications

    SciTech Connect

    Tang, Zhihong

    2007-01-01

    Transition metal silicides are being considered for future engine turbine components at temperatures up to 1600 C. Although significant improvement in high temperature strength, room temperature fracture toughness has been realized in the past decade, further improvement in oxidation resistance is needed. Oxidation mechanism of Ti5Si3-based alloys was investigated. Oxidation behavior of Ti5Si3-based alloy strongly depends on the atmosphere. Presence of Nitrogen alters the oxidation behavior of Ti5Si3 by nucleation and growth of nitride subscale. Ti5Si3.2and Ti5Si3C0.5 alloys exhibited an excellent oxidation resistance in nitrogen bearing atmosphere due to limited dissolution of nitrogen and increased Si/Ti activity ratio. MoSi2 coating developed by pack cementation to protect Mo-based Mo-Si-B composites was found to be effective up to 1500 C. Shifting coating composition to T1+T2+Mo3Si region showed the possibility to extend the coating lifetime above 1500 C by more than ten times via formation of slow growing Mo3Si or T2 interlayer without sacrificing the oxidation resistance of the coating. The phase equilibria in the Nb-rich portion of Nb-B system has been evaluated experimentally using metallographic analysis and differential thermal analyzer (DTA). It was shown that Nbss (solid solution) and NbB are the only two primary phases in the 0-40 at.% B composition range, and the eutectic reaction L {leftrightarrow} NbSS + NbB was determined to occur at 2104 ± 5 C by DTA.

  16. Transition metal coordination polymers based on tetrabromoterephthalic and bis(imidazole) ligands: Syntheses, structures, topological analysis and photoluminescence properties

    NASA Astrophysics Data System (ADS)

    Zhang, Xiaowei; Xing, Peiqi; Geng, Xiujuan; Sun, Daofeng; Xiao, Zhenyu; Wang, Lei

    2015-09-01

    Eight new coordination polymers (CPs), namely, [Zn(1,2-mbix)(tbtpa)]n (1), [Co(1,2-mbix)(tbtpa)]n (2), [CdCl(1,2-mbix)(tbtpa)0.5]n (3), {[Cd(1,2-bix)(tbtpa)]·H2O}n (4), {[Cd0.5(1,2-bix)(tbtpa)0.5]·H2O}n (5), {[Co0.5(1,2-bix)(tbtpa)0.5]·2H2O}n (6), {[Co(1,2-bix)(tbtpa)]·H2O}n (7) and {[Co(1,2-bix)(tbtpa)]·Diox·2H2O}n (8), were synthesized under solvothermal conditions based on mix-ligand strategy (H2tbtpa=tetrabromoterephthalic acid and 1,2-mbix=1,2-bis((2-methyl-1H-imidazol-1-yl)methyl)benzene, 1,2-bix=1,2-bis(imidazol-1-ylmethyl)benzene). All of the CPs have been structurally characterized by single-crystal X-ray diffraction analyses and further characterized by elemental analyses, IR spectroscopy, powder X-ray diffraction (PXRD), and thermogravimetric analyses (TGA). X-ray diffraction analyses show that 1 and 2 are isotypics which have 2D highly undulated networks with (4,4)-sql topology with the existence of C-H ⋯Br interactions; for 3, it has a 2D planar network with (4,4)-sql topology with the occurrence of C-H ⋯Cl interactions other than C-H ⋯Br interactions; 4 shows a 3D 2-fold interpenetrated nets with rare 65·8-mok topology which has a self-catention property. As the same case as 1 and 2, 5 and 6 are also isostructural with planar layers with 44-sql topology which further assembled into 3D supramolecular structure through the interdigitated stacking fashion and the C-Br ⋯Cph interactions. As for 7, it has a 2D slightly undulated networks with (4,4)-sql topology which has one dimension channel. While 8 has a 2-fold interpenetrated networks with (3,4)-connect jeb topology with point symbol {63}{65·8}. And their structures can be tuned by conformations of bis(imidazol) ligands and solvent mixture. Besides, the TGA properties for all compounds and the luminescent properties for 1, 3, 4, 5 are discussed in detail.

  17. Enhancing conductivity of metallic carbon nanotube networks by transition metal adsorption.

    PubMed

    Ketolainen, T; Havu, V; Puska, M J

    2015-02-01

    The conductivity of carbon nanotube thin films is mainly determined by carbon nanotube junctions, the resistance of which can be reduced by several different methods. We investigate electronic transport through carbon nanotube junctions in a four-terminal configuration, where two metallic single-wall carbon nanotubes are linked by a group 6 transition metal atom. The transport calculations are based on the Green's function method combined with the density-functional theory. The transition metal atom is found to enhance the transport through the junction near the Fermi level. However, the size of the nanotube affects the improvement in the conductivity. The enhancement is related to the hybridization of chromium and carbon atom orbitals, which is clearly reflected in the character of eigenstates near the Fermi level. The effects of chromium atoms and precursor molecules remaining adsorbed on the nanotubes outside the junctions are also examined. PMID:25662658

  18. Enhancing conductivity of metallic carbon nanotube networks by transition metal adsorption

    SciTech Connect

    Ketolainen, T. Havu, V.; Puska, M. J.

    2015-02-07

    The conductivity of carbon nanotube thin films is mainly determined by carbon nanotube junctions, the resistance of which can be reduced by several different methods. We investigate electronic transport through carbon nanotube junctions in a four-terminal configuration, where two metallic single-wall carbon nanotubes are linked by a group 6 transition metal atom. The transport calculations are based on the Green’s function method combined with the density-functional theory. The transition metal atom is found to enhance the transport through the junction near the Fermi level. However, the size of the nanotube affects the improvement in the conductivity. The enhancement is related to the hybridization of chromium and carbon atom orbitals, which is clearly reflected in the character of eigenstates near the Fermi level. The effects of chromium atoms and precursor molecules remaining adsorbed on the nanotubes outside the junctions are also examined.

  19. Resonant Ultrasound Studies of Complex Transition Metal Oxides

    SciTech Connect

    Dr. Henry Bass; Dr. J. R. Gladden

    2008-08-18

    Department of Energy EPSCoR The University of Mississippi Award: DE-FG02-04ER46121 Resonant Ultrasound Spectroscopy Studies of Complex Transition Metal Oxides The central thrust of this DOE funded research program has been to apply resonant ultrasound spectroscopy (RUS), an elegant and efficient method for determining the elastic stiffness constants of a crystal, to the complex and poorly understood class of materials known as transition metal oxides (TMOs). Perhaps the most interesting and challenging feature of TMOs is their strongly correlated behavior in which spin, lattice, and charge degrees of freedom are strongly coupled. Elastic constants are a measure of the interatomic potentials in a crystal and are thus sensitive probes into the atomic environment. This sensitivity makes RUS an ideal tool to study the coupling of phase transition order parameters to lattice strains. The most significant result of the project has been the construction of a high temperature RUS apparatus capable of making elastic constant measurements at temperatures as high as 1000 degrees Celsius. We have designed and built novel acoustic transducers which can operate as high as 600 degrees Celsius based on lithium niobate piezoelectric elements. For measurement between 600 to 1000 C, a buffer rod system is used in which the samples under test and transducers are separated by a rod with low acoustic attenuation. The high temperature RUS system has been used to study the charge order (CO) transition in transition metal oxides for which we have discovered a new transition occurring about 35 C below the CO transition. While the CO transition exhibits a linear coupling between the strain and order parameter, this new precursor transition shows a different coupling indicating a fundamentally different mechanism. We have also begun a study, in collaboration with the Jet Propulsion Laboratory, to study novel thermoelectric materials at elevated temperatures. These materials include silicon

  20. Studies on DNA binding behaviour of biologically active transition metal complexes of new tetradentate N2O2 donor Schiff bases: Inhibitory activity against bacteria

    NASA Astrophysics Data System (ADS)

    Sobha, S.; Mahalakshmi, R.; Raman, N.

    A series of Cu(II), Ni(II) and Zn(II) complexes of the type ML have been synthesized with Schiff bases derived from o-acetoacetotoluidide, 2-hydroxybenzaldehyde and o-phenylenediamine/1,4-diaminobutane. The complexes are insoluble in common organic solvents but soluble in DMF and DMSO. The measured molar conductance values in DMSO indicate that the complexes are non-electrolytic in nature. All the six metal complexes have been fully characterized with the help of elemental analyses, molecular weights, molar conductance values, magnetic moments and spectroscopic data. The analytical data helped to elucidate the structure of the metal complexes. The Schiff bases are found to act as tetradentate ligands using N2O2 donor set of atoms leading to a square-planar geometry for the complexes around all the metal ions. The binding properties of metal complexes with DNA were investigated by absorption spectra, viscosity measurements and cyclic voltammetry. Detailed analysis reveals that the metal complexes intercalate into the DNA base stack as intercalators. All the metal complexes cleave the pUC19 DNA in presence of H2O2. The Schiff bases and their complexes have been screened for their antibacterial activity against five bacterial strains (Staphylococcus aureus, Pseudomonas aeruginosa, Escherichia coli, Staphylococcus epidermidis, Klebsiella pneumoniae) by disk diffusion method. All the metal complexes have potent biocidal activity than the free ligands.

  1. Trends in Ionization Energy of Transition-Metal Elements

    ERIC Educational Resources Information Center

    Matsumoto, Paul S.

    2005-01-01

    A rationale for the difference in the periodic trends in the ionization energy of the transition-metal elements versus the main-group elements is presented. The difference is that in the transition-metal elements, the electrons enter an inner-shell electron orbital, while in the main-group elements, the electrons enter an outer-shell electron…

  2. Nanostructured transition metal oxides useful for water oxidation catalysis

    DOEpatents

    Frei, Heinz M; Jiao, Feng

    2013-12-24

    The present invention provides for a composition comprising a nanostructured transition metal oxide capable of oxidizing two H.sub.2O molecules to obtain four protons. In some embodiments of the invention, the composition further comprises a porous matrix wherein the nanocluster of the transition metal oxide is embedded on and/or in the porous matrix.

  3. Nutritional immunity: transition metals at the pathogen-host interface

    PubMed Central

    Hood, M. Indriati; Skaar, Eric P.

    2013-01-01

    Transition metals occupy an essential niche in biological systems. Their electrostatic properties stabilize substrates or reaction intermediates in the active sites of enzymes, while their heightened reactivity is harnessed for catalysis. However, the latter property renders transition metals toxic at high concentrations. Bacteria, like all living organisms, must regulate the levels of these elements to satisfy their physiological needs while avoiding harm. It is therefore not surprising that the host capitalizes on both the essentiality and toxicity of transition metals to defend against bacterial invaders. This review will discuss established and emerging paradigms in nutrient metal homeostasis at the pathogen-host interface. PMID:22796883

  4. Transition metal complexes of isonicotinic acid (2-hydroxybenzylidene)hydrazide.

    PubMed

    Abou-Melha, Khlood S

    2008-06-01

    A new series of transition metal complexes of Schiff base isonicotinic acid (2-hydroxybenzylidene)hydrazide, HL, have been synthesized. The Schiff base reacted with Cu(II), Ni(II), Co(II), Mn(II), Fe(III) and UO2(II) ions as monobasic tridentate ligand to yield mononuclear complexes of 1:2 (metal:ligand) except that of Cu(II) which form complex of 1:1 (metal:ligand). The ligand and its metal complexes were characterized by elemental analyses, IR, UV-vis, mass and 1H NMR spectra, as well as magnetic moment, conductance measurements, and thermal analyses. All complexes have octahedral configurations except Cu(II) complex which has an extra square planar geometry distorted towards tetrahedral. While, the UO2(II) complex has its favour hepta-coordination. The ligand and its metal complexes were tested against one strain Gram +ve bacteria (Staphylococcus aureus), Gram -ve bacteria (Escherichia coli), and Fungi (Candida albicans). The tested compounds exhibited higher antibacterial activities. PMID:17728178

  5. Transition metal complexes of isonicotinic acid (2-hydroxybenzylidene)hydrazide

    NASA Astrophysics Data System (ADS)

    Abou-Melha, Khlood S.

    2008-06-01

    A new series of transition metal complexes of Schiff base isonicotinic acid (2-hydroxybenzylidene)hydrazide, HL, have been synthesized. The Schiff base reacted with Cu(II), Ni(II), Co(II), Mn(II), Fe(III) and UO 2(II) ions as monobasic tridentate ligand to yield mononuclear complexes of 1:2 (metal:ligand) except that of Cu(II) which form complex of 1:1 (metal:ligand). The ligand and its metal complexes were characterized by elemental analyses, IR, UV-vis, mass and 1H NMR spectra, as well as magnetic moment, conductance measurements, and thermal analyses. All complexes have octahedral configurations except Cu(II) complex which has an extra square planar geometry distorted towards tetrahedral. While, the UO 2(II) complex has its favour hepta-coordination. The ligand and its metal complexes were tested against one strain Gram +ve bacteria ( Staphylococcus aureus), Gram -ve bacteria (Escherichia coli) , and Fungi ( Candida albicans). The tested compounds exhibited higher antibacterial activities.

  6. Syntheses, structures, and properties of transition metal coordination polymers based on a long semirigid tetracarboxylic acid and multidentate N-donor ligands

    NASA Astrophysics Data System (ADS)

    Gao, Peng; Bai, Hui; Bing, Ying-Ying; Hu, Ming

    2016-02-01

    Six transition metal coordination polymers based on a semirigid tetracarboxylic acid and the multidentate N-donor ligands have been synthesized by the hydrothermal method, namely, {[Co(H2obda) (μ2-H2O) (H2O)2]·2H2O}n (1), {[Co(obda)0.5(bpe) (H2O)2]·3H2O}n (2), {[Zn(H2obda) (H2O)4]·H4obda·6H2O}n (3), {[Zn(bpy) (H2O)4]·H2obda}n (4), {[Ni(bpy) (H2O)4]·H2obda}n (5) and {[Cu(H2obda) (bpy)2]}n (6) (H4obda = 1,4-bis(4-oxy-1,2-benzene dicarboxylic acid)benzene, bpe = 1,2-Bis(4-pyridyl)ethylene), bpy = 4,4‧-bipyridine). Compounds 1-6 were structurally characterized by the elemental analyses, infrared spectra, and single crystal X-ray diffractions. Compounds 1-2 exhibit the 2D quadrilateral and polygonal layered grid structures, respectively; a 3D supramolecular structure of 2 has been build via π···π and hydrogen bonds interactions. Compounds 3-6 reveal the 1D zigzag and linear chains structures, respectively; furthermore, 3-5 display the diverse 3D supramolecular structures via hydrogen bonds, respectively. The 1-D infinite water chain in 3 has been found between the lattice water molecules. In addition, the thermogravimetric analyses of 1-6, magnetic property of 1, and photoluminescence of 3-4 have been investigated, respectively.

  7. Density functional plus dynamical mean-field theory of the metal-insulator transition in early transition-metal oxides

    NASA Astrophysics Data System (ADS)

    Dang, Hung T.; Ai, Xinyuan; Millis, Andrew J.; Marianetti, Chris A.

    2014-09-01

    The combination of density functional theory and single-site dynamical mean-field theory, using both Hartree and full continuous-time quantum Monte Carlo impurity solvers, is used to study the metal-insulator phase diagram of perovskite transition-metal oxides of the form ABO3 with a rare-earth ion A =Sr, La, Y and transition metal B =Ti, V, Cr. The correlated subspace is constructed from atomiclike d orbitals defined using maximally localized Wannier functions derived from the full p-d manifold; for comparison, results obtained using a projector method are also given. Paramagnetic DFT + DMFT computations using full charge self-consistency along with the standard "fully localized limit" (FLL) double counting are shown to incorrectly predict that LaTiO3, YTiO3, LaVO3, and SrMnO3 are metals. A more general examination of the dependence of physical properties on the mean p-d energy splitting, the occupancy of the correlated d states, the double-counting correction, and the lattice structure demonstrates the importance of charge-transfer physics even in the early transition-metal oxides and elucidates the factors underlying the failure of the standard approximations. If the double counting is chosen to produce a p-d splitting consistent with experimental spectra, single-site dynamical mean-field theory provides a reasonable account of the materials properties. The relation of the results to those obtained from "d-only" models in which the correlation problem is based on the frontier orbital p-d antibonding bands is determined. It is found that if an effective interaction U is properly chosen the d-only model provides a good account of the physics of the d1 and d2 materials.

  8. Patterning Superatom Dopants on Transition Metal Dichalcogenides.

    PubMed

    Yu, Jaeeun; Lee, Chul-Ho; Bouilly, Delphine; Han, Minyong; Kim, Philip; Steigerwald, Michael L; Roy, Xavier; Nuckolls, Colin

    2016-05-11

    This study describes a new and simple approach to dope two-dimensional transition metal dichalcogenides (TMDCs) using the superatom Co6Se8(PEt3)6 as the electron dopant. Semiconducting TMDCs are wired into field-effect transistor devices and then immersed into a solution of these superatoms. The degree of doping is determined by the concentration of the superatoms in solution and by the length of time the films are immersed in the dopant solution. Using this chemical approach, we are able to turn mono- and few-layer MoS2 samples from moderately to heavily electron-doped states. The same approach applied on WSe2 films changes their characteristics from hole transporting to electron transporting. Moreover, we show that the superatom doping can be patterned on specific areas of TMDC films. To illustrate the power of this technique, we demonstrate the fabrication of a lateral p-n junction by selectively doping only a portion of the channel in a WSe2 device. Finally, encapsulation of the doped films with crystalline hydrocarbon layers stabilizes their properties in an ambient environment. PMID:27082448

  9. Transition metal-free olefin polymerization catalyst

    DOEpatents

    Sen, Ayusman; Wojcinski, II, Louis M.; Liu, Shengsheng

    2001-01-01

    Ethylene and/or propylene are polymerized to form high molecular weight, linear polymers by contacting ethylene and/or propylene monomer, in the presence of an inert reaction medium, with a catalyst system which consists essentially of (1) an aluminum alkyl component, such as trimethylaluminum, triethylaluminum, triisobutylaluminum, tri-n-octylaluminum and diethylaluminum hydride and (2) a Lewis acid or Lewis acid derivative component, such as B (C.sub.6 F.sub.5).sub.3, [(CH.sub.3).sub.2 N (H) (C.sub.6 H.sub.5)].sup.+ [B (C.sub.6 F.sub.5)4].sup.-, [(C.sub.2 H.sub.5).sub.3 NH].sup.+ [B C.sub.6 F.sub.5).sub.4 ],.sup.-, [C(C.sub.6 F.sub.5).sub.3 ].sup.+ [B(C.sub.6 F.sub.5).sub.4 ].sup.-, (C.sub.2 H.sub.5).sub.2 Al(OCH.sub.3), (C.sub.2 H.sub.5).sub.2 Al(2,6-di-t-butyl-4-methylphenoxide), (C.sub.2 H.sub.5)Al(2,6 -di-t-butylphenoxide).sub.2, (C.sub.2 H.sub.5).sub.2 Al(2,6-di-t-butylphonoxide) , 2,6 -di-t-butylphenol.multidot.methylaluminoxane or an alkylaluminoxane, and which may be completely free any transition metal component(s).

  10. Trion formation in monolayer transition metal dichalcogenides

    NASA Astrophysics Data System (ADS)

    Kezerashvili, Roman Ya.; Tsiklauri, Shalva M.

    We present three-body calculations for trions binding energy in monolayer transition metal dichalcogenides using the method of hyperspherical harmonics (HH). In numerical calculations for a proper treatment of Coulomb screening in two dimensions we assume that electrons and holes are interacted via Keldysh potential. The convergences of binding energy calculations for the ground state of the trion as a function of the grand angular momentum are studied. For the trion binding energy in MoS2 we obtain 19.2 mev. This value is remarkably close to the experimental one of 18 meV. A comparison with results of other calculations are presented. We also study solutions of a hyperradial equation in a minimal approximation for the ground angular momentum to examine two regimes: a long range and a short range cases when the inter particle distance is much greater and much less than the screening length. For these cases, we find analytical expressions for the energy and wave function for trion states

  11. Impact Electrochemistry of Layered Transition Metal Dichalcogenides.

    PubMed

    Lim, Chee Shan; Tan, Shu Min; Sofer, Zdeněk; Pumera, Martin

    2015-08-25

    Layered transition metal dichalcogenides (TMDs) exhibit paramount importance in the electrocatalysis of the hydrogen evolution reaction. It is crucial to determine the size of the electrocatalytic particles as well as to establish their electrocatalytic activity, which occurs at the edges of these particles. Here, we show that individual TMD (MoS2, MoSe2, WS2, or WSe2; in general MX2) nanoparticles impacting an electrode surface provide well-defined current "spikes" in both the cathodic and anodic regions. These spikes originate from direct oxidation of the nanoparticles (from M(4+) to M(6+)) at the anodic region and from the electrocatalytic currents generated upon hydrogen evolution in the cathodic region. The positive correlation between the frequency of the impacts and the concentration of TMD nanoparticles is also demonstrated here, enabling determination of the concentration of TMD nanoparticles in colloidal form. In addition, the size of individual TMD nanoparticles can be evaluated using the charge passed during every spike. The capability of detecting both the "indirect" catalytic effect of an impacting TMD nanoparticle as well as "direct" oxidation indicates that the frequency of impacts in both the "indirect" and "direct" scenarios are comparable. This suggests that all TMD nanoparticles, which are electrochemically oxidizable (thus capable of donating electrons to electrodes), are also capable of catalyzing the hydrogen reduction reaction. PMID:26241193

  12. Modern Transition-Metal-Catalyzed Carbon-Halogen Bond Formation.

    PubMed

    Petrone, David A; Ye, Juntao; Lautens, Mark

    2016-07-27

    The high utility of halogenated organic compounds has prompted the development of a vast number of transformations which install the carbon-halogen motif. Traditional routes to these building blocks have commonly involved multiple steps, harsh reaction conditions, and the use of stoichiometric and/or toxic reagents. In this regard, using transition metals to catalyze the synthesis of organohalides has become a mature field in itself, and applying these technologies has allowed for a decrease in the production of waste, higher levels of regio- and stereoselectivity, and the ability to produce enantioenriched target compounds. Furthermore, transition metals offer the distinct advantage of possessing a diverse spectrum of mechanistic possibilities which translate to the capability to apply new substrate classes and afford novel and difficult-to-access structures. This Review provides comprehensive coverage of modern transition metal-catalyzed syntheses of organohalides via a diverse array of mechanisms. Attention is given to the seminal stoichiometric organometallic studies which led to the corresponding catalytic processes being realized. By breaking this field down into the synthesis of aryl, vinyl, and alkyl halides, it becomes clear which methods have surfaced as most favored for each individual class. In general, a pronounced shift toward the use of C-H bonds as key functional groups, in addition to methods which proceed by catalytic, radical-based mechanisms has occurred. Although always evolving, this field appears to be heading in the direction of using starting materials with a significantly lower degree of prefunctionalization in addition to less expensive and abundant metal catalysts. PMID:27341176

  13. Correlated electron pseudopotentials for 3d-transition metals

    SciTech Connect

    Trail, J. R. Needs, R. J.

    2015-02-14

    A recently published correlated electron pseudopotentials (CEPPs) method has been adapted for application to the 3d-transition metals, and to include relativistic effects. New CEPPs are reported for the atoms Sc − Fe, constructed from atomic quantum chemical calculations that include an accurate description of correlated electrons. Dissociation energies, molecular geometries, and zero-point vibrational energies of small molecules are compared with all electron results, with all quantities evaluated using coupled cluster singles doubles and triples calculations. The CEPPs give better results in the correlated-electron calculations than Hartree-Fock-based pseudopotentials available in the literature.

  14. Cross-plane thermal properties of transition metal dichalcogenides

    SciTech Connect

    Muratore, C.; Varshney, V.; Gengler, J. J.; Hu, J. J.; Bultman, J. E.; Smith, T. M.; Shamberger, P. J.; Roy, A. K.; Voevodin, A. A.; Qiu, B.; Ruan, X.

    2013-02-25

    In this work, we explore the thermal properties of hexagonal transition metal dichalcogenide compounds with different average atomic masses but equivalent microstructures. Thermal conductivity values of sputtered thin films were compared to bulk crystals. The comparison revealed a >10 fold reduction in thin film thermal conductivity. Structural analysis of the films revealed a turbostratic structure with domain sizes on the order of 5-10 nm. Estimates of phonon scattering lengths at domain boundaries based on computationally derived group velocities were consistent with the observed film microstructure, and accounted for the reduction in thermal conductivity compared to values for bulk crystals.

  15. Correlated electron pseudopotentials for 3d-transition metals

    NASA Astrophysics Data System (ADS)

    Trail, J. R.; Needs, R. J.

    2015-02-01

    A recently published correlated electron pseudopotentials (CEPPs) method has been adapted for application to the 3d-transition metals, and to include relativistic effects. New CEPPs are reported for the atoms Sc - Fe, constructed from atomic quantum chemical calculations that include an accurate description of correlated electrons. Dissociation energies, molecular geometries, and zero-point vibrational energies of small molecules are compared with all electron results, with all quantities evaluated using coupled cluster singles doubles and triples calculations. The CEPPs give better results in the correlated-electron calculations than Hartree-Fock-based pseudopotentials available in the literature.

  16. Storing excitons in transition-metal dichalcogenides using dark states

    NASA Astrophysics Data System (ADS)

    Gunlycke, Daniel; Tseng, Frank; Simsek, Ergun

    Monolayer transition-metal dichalcogenides exhibit strongly bound excitons confined to two dimensions. One challenge in exploiting these excitons is that they have a finite life time and collapse through electron-hole recombination. We propose that the exciton life time could be extended by transitioning the exciton population into dark states. The symmetry of these dark states require the electron and hole to be spatially separated, which not only causes these states to be optically inactive but also inhibits electron-hole recombination. Based on an atomistic model we call the Triangular Lattice Exciton (3ALE) model, we derive transition matrix elements and approximate selection rules showing that excitons could be transitioned into and out of dark states using a pulsed infrared laser. For illustration, we also present exciton population scenarios based on different recombination decay constants. Longer exciton lifetimes could make these materials candidates for applications in energy management and quantum information processing. This work was supported by the Office of Naval Research, directly and through the Naval Research Laboratory.

  17. Solid-solid phase transitions via melting in metals.

    PubMed

    Pogatscher, S; Leutenegger, D; Schawe, J E K; Uggowitzer, P J; Löffler, J F

    2016-01-01

    Observing solid-solid phase transitions in-situ with sufficient temporal and spatial resolution is a great challenge, and is often only possible via computer simulations or in model systems. Recently, a study of polymeric colloidal particles, where the particles mimic atoms, revealed an intermediate liquid state in the transition from one solid to another. While not yet observed there, this finding suggests that such phenomena may also occur in metals and alloys. Here we present experimental evidence for a solid-solid transition via the formation of a metastable liquid in a 'real' atomic system. We observe this transition in a bulk glass-forming metallic system in-situ using fast differential scanning calorimetry. We investigate the corresponding transformation kinetics and discuss the underlying thermodynamics. The mechanism is likely to be a feature of many metallic glasses and metals in general, and may provide further insight into phase transition theory. PMID:27103085

  18. Solid–solid phase transitions via melting in metals

    PubMed Central

    Pogatscher, S.; Leutenegger, D.; Schawe, J. E. K.; Uggowitzer, P. J.; Löffler, J. F.

    2016-01-01

    Observing solid–solid phase transitions in-situ with sufficient temporal and spatial resolution is a great challenge, and is often only possible via computer simulations or in model systems. Recently, a study of polymeric colloidal particles, where the particles mimic atoms, revealed an intermediate liquid state in the transition from one solid to another. While not yet observed there, this finding suggests that such phenomena may also occur in metals and alloys. Here we present experimental evidence for a solid–solid transition via the formation of a metastable liquid in a ‘real' atomic system. We observe this transition in a bulk glass-forming metallic system in-situ using fast differential scanning calorimetry. We investigate the corresponding transformation kinetics and discuss the underlying thermodynamics. The mechanism is likely to be a feature of many metallic glasses and metals in general, and may provide further insight into phase transition theory. PMID:27103085

  19. Polyoxometalate-based organic-inorganic hybrid compounds containing transition metal mixed-organic-ligand complexes of N-containing and pyridinecarboxylate ligands.

    PubMed

    Zhao, De-Chuan; Hu, Yang-Yang; Ding, Hong; Guo, Hai-Yang; Cui, Xiao-Bing; Zhang, Xiao; Huo, Qi-Sheng; Xu, Ji-Qing

    2015-05-21

    Five new organic–inorganic hybrid compounds based on the Keggin-type polyoxoanion [SiW12O40]4−, namely [Cu3(2,2′-bpy)3(inic)(μ2-OH)(H2O)][SiW12O40]·2H2O (1), [Cu6(phen)6(μ3-Cl)2(μ2-Cl)2Cl2(inic)2][SiW12O40]·6H2O (2), [Cu2(hnic)(2,2′-bpy)2Cl]2[H2SiW12O40] (3), [Cu2(nic)(phen)2Cl2]2[SiW12O40] (4) and [Cu2(pic)(2,2′-bpy)2Cl]2[SiW12O40] (5) (inic = isonicotinic acid, hnic = 2-hydroxy-nicotinic acid, nic = nicotinic acid, pic = picolinic acid, 2,2′-bpy = 2,2′-bipyridine, phen = 1,10-phenanthroline) have been synthesized and characterized by IR, UV-Vis, XPS, XRD, cyclic voltammetric measurements, photoluminescence analysis and single crystal X-ray diffraction analysis. Crystal analysis reveals that compound 1 exhibits a 2-D double layered framework structure constructed from [SiW12O40]4− and copper-aqua-2,2′-bipy-hydroxyl-isonicotinate complexes. Compound 2 is a 0-D discrete structure formed by [SiW12O40]4− and copper-chloro-isonicotinate-phenanthroline complexes. Compound 3 shows a 1-D single chain structure based on the linkage of copper-2,2-bpy-chloro-2-hydroxy-nicotinate complexes and [SiW12O40]4−. Compounds 4 and 5 both contain polyoxometalate supported transition metal complexes, one is a polyoxometalate supported copper-chloro-nicotinate-phenanthroline complex in 4, and the other is a polyoxometalate supported copper-2,2-bpy-chloro-nicotinate complex in 5. It should be noted that nicotinic, isonicotinic and picolinic acids are structural isomers and 2-hydroxy-nicotinic acid is an in situ hydroxylated product of nicotinic acid. In addition, photocatalytic degradation of Rhodamine B (RhB) by compounds 1–5 has been investigated in aqueous solutions. PMID:25882351

  20. Transition-Metal-Doped p-Type ZnO Nanoparticle-Based Sensory Array for Instant Discrimination of Explosive Vapors.

    PubMed

    Qu, Jiang; Ge, Yuru; Zu, Baiyi; Li, Yuxiang; Dou, Xincun

    2016-03-01

    The development of portable, real-time, and cheap platforms to monitor ultratrace levels of explosives is of great urgence and importance due to the threat of terrorism attacks and the need for homeland security. However, most of the previous chemiresistor sensors for explosive detection are suffering from limited responses and long response time. Here, a transition-metal-doping method is presented to remarkably promote the quantity of the surface defect states and to significantly reduce the charge transfer distance by creating a local charge reservoir layer. Thus, the sensor response is greatly enhanced and the response time is remarkably shortened. The resulting sensory array can not only detect military explosives, such as, TNT, DNT, PNT, PA, and RDX with high response, but also can fully distinguish some of the improvised explosive vapors, such as AN and urea, due to the huge response reaching to 100%. Furthermore, this sensory array can discriminate ppb-level TNT and ppt-level RDX from structurally similar and high-concentration interfering aromatic gases in less than 12 s. Through comparison with the previously reported chemiresistor or Schottky sensors for explosive detection, the present transition-metal-doping method resulting ZnO sensor stands out and undoubtedly challenges the best. PMID:26763156

  1. Hyperfine structure studies of transition metals

    SciTech Connect

    Young, L.; Kurtz, C.; Hasegawa, S.

    1995-08-01

    This past year our studies of hyperfine structure (hfs) in metastable states of transition metals concentrated on the analysis of hfs in the four-valence electron system, Nb II. Earlier, we measured hfs intervals using the laser-rf double resonance and laser-induced fluorescence methods in a fast-ion beam of Nb{sup +}. The resulting experimental magnetic dipole and electric quadrupole interaction constants are compared to those calculated by a relativistic configuration interaction approach. These are the first hfs data on this refractory element. Theoretically, it is found that the most important contributions to the energy are the pair excitations, valence single excitations and core polarization from the shallow core. However, the inner core polarization is found to be crucial for hfs, albeit unimportant for energy. For the J=2 level at 12805 cm{sup -1}, 4d{sup 4} {sup 3}F. the theoretical relativistic configuration A-value is in agreement with the experimental result to an accuracy of 4%. Other calculated A-values are expected to be of the same accuracy. A paper describing these results was accepted for publication. Experimental studies of the four-valence electron system V{sup +} in the (4s+3d){sup 4} manifold are complete. The theoretical difficulties for the 3d manifold, noted earlier for the three-valence electron Ti{sup +}, as compared to the 4d manifold appear to be repeated in the case of the four-valence electron systems (Nb{sup +} and V{sup +}). Relativistic configuration interaction calculations are underway, after which a paper will be published.

  2. Multifunctional Ligands in Transition Metal Catalysis (invited 'Focus' article),

    SciTech Connect

    Crabtree, Robert H

    2011-01-01

    Sophisticated ligands are now being designed that do far more than just fulfil their traditional spectator roles by binding to the metal and providing a sterically-defined binding pocket for the substrate in homogeneous transition metal catalysis. This Focus review emphasizes selected cases in which ligands carry additional functional groups that change the properties of the ligand as a result of an external stimulus or undergo catalytically-relevant ligand-based reactivity. These include proton responsive ligands capable of gaining or losing one or more protons, ligands having a hydrogen bonding function, electroresponsive ligands capable of gaining or losing one or more electrons, and photoresponsive ligands capable of undergoing a useful change of properties upon irradiation. Molecular recognition ligands and proton coupled electron transfer (PCET) are briefly discussed.

  3. Transition Metal-Free Tryptophan-Selective Bioconjugation of Proteins.

    PubMed

    Seki, Yohei; Ishiyama, Takashi; Sasaki, Daisuke; Abe, Junpei; Sohma, Youhei; Oisaki, Kounosuke; Kanai, Motomu

    2016-08-31

    Chemical modifications of native proteins can facilitate production of supernatural protein functions that are not easily accessible by complementary methods relying on genetic manipulations. However, accomplishing precise control over selectivity while maintaining structural integrity and homogeneity still represents a formidable challenge. Herein, we report a transition metal-free method for tryptophan-selective bioconjugation of proteins that is based on an organoradical and operates under ambient conditions. This method exhibits low levels of cross-reactivity and leaves higher-order structures of the protein and various functional groups therein unaffected. The strategy to target less abundant amino acids contributes to the formation of structurally homogeneous conjugates, which may even be suitable for protein crystallography. The absence of toxic metals and biochemically incompatible conditions allows a rapid functional modulation of native proteins such as antibodies and pathogenic aggregative proteins, and this method may thus easily find therapeutic applications. PMID:27534812

  4. Process for making transition metal nitride whiskers

    DOEpatents

    Bamberger, C.E.

    1988-04-12

    A process for making metal nitrides, particularly titanium nitride whiskers, using a cyanide salt as a reducing agent for a metal compound in the presence of an alkali metal oxide. Sodium cyanide, various titanates and titanium oxide mixed with sodium oxide react to provide titanium nitride whiskers that can be used as reinforcement to ceramic composites. 1 fig., 1 tab.

  5. Process for making transition metal nitride whiskers

    SciTech Connect

    Bamberger, Carlos E.

    1989-01-01

    A process for making metal nitrides, particularly titanium nitride whiskers, using a cyanide salt as a reducing agent for a metal compound in the presence of an alkali metal oxide. Sodium cyanide, various titanates and titanium oxide mixed with sodium oxide react to provide titanium nitride whiskers that can be used as reinforcement to ceramic composites.

  6. Correlation-induced metal-insulator transitions in d0 magnetic superlattices based on alkaline-earth monoxides: Insights from ab initio calculations

    NASA Astrophysics Data System (ADS)

    Lu, Yi-Lin; Dong, Shengjie; Zhou, Baozeng; Zhao, Hui; Wu, Ping

    2015-06-01

    Using first-principles density functional theory calculations, we have investigated the electronic structure and magnetic properties of four superlattices (MO)1/(MX)1 (001) (M=Ca and Sr; X=N and C). Our results show that compared with standard GGA approach, the GGA plus effective Ueff scheme can correct electronic structure and magnetic properties in some extent. With enhancing electronic correlation, for (CaO)1/(CaN)1, (SrO)1/(SrN)1, and (SrO)1/(SrC)1, the bands across Fermi level are divided into two parts and the shape of isotropic spherical spin atmosphere becomes anisotropic dumbbell-like with specific orientation, accompanying metal-insulator transitions. For (CaO)1/(CaC)1, the states just smearing with the Fermi level shift to lower energy region below Fermi level, indicating the transformation from a nearly half metal to an actual half metal occurs. The different behavior of (CaO)1/(CaC)1 compared with three other compounds may be caused by the larger ionization energy of calcium than that of strontium and the smaller electronegativity of carbon than that of nitrogen.

  7. Chiral phase transition in lattice QCD as a metal-insulator transition

    SciTech Connect

    Garcia-Garcia, Antonio M.; Osborn, James C.

    2007-02-01

    We investigate the lattice QCD Dirac operator with staggered fermions at temperatures around the chiral phase transition. We present evidence of a metal-insulator transition in the low lying modes of the Dirac operator around the same temperature as the chiral phase transition. This strongly suggests the phenomenon of Anderson localization drives the QCD vacuum to the chirally symmetric phase in a way similar to a metal-insulator transition in a disordered conductor. We also discuss how Anderson localization affects the usual phenomenological treatment of phase transitions a la Ginzburg-Landau.

  8. Gold based bulk metallic glass

    SciTech Connect

    Schroers, Jan; Lohwongwatana, Boonrat; Johnson, William L.; Peker, Atakan

    2005-08-08

    Gold-based bulk metallic glass alloys based on Au-Cu-Si are introduced. The alloys exhibit a gold content comparable to 18-karat gold. They show very low liquidus temperature, large supercooled liquid region, and good processibility. The maximum casting thickness exceeds 5 mm in the best glassformer. Au{sub 49}Ag{sub 5.5}Pd{sub 2.3}Cu{sub 26.9}Si{sub 16.3} has a liquidus temperature of 644 K, a glass transition temperature of 401 K, and a supercooled liquid region of 58 K. The Vickers hardness of the alloys in this system is {approx}350 Hv, twice that of conventional 18-karat crystalline gold alloys. This combination of properties makes the alloys attractive for many applications including electronic, medical, dental, surface coating, and jewelry.

  9. Gold based bulk metallic glass

    NASA Astrophysics Data System (ADS)

    Schroers, Jan; Lohwongwatana, Boonrat; Johnson, William L.; Peker, Atakan

    2005-08-01

    Gold-based bulk metallic glass alloys based on Au-Cu-Si are introduced. The alloys exhibit a gold content comparable to 18-karat gold. They show very low liquidus temperature, large supercooled liquid region, and good processibility. The maximum casting thickness exceeds 5mm in the best glassformer. Au49Ag5.5Pd2.3Cu26.9Si16.3 has a liquidus temperature of 644K, a glass transition temperature of 401K, and a supercooled liquid region of 58K. The Vickers hardness of the alloys in this system is ˜350Hv, twice that of conventional 18-karat crystalline gold alloys. This combination of properties makes the alloys attractive for many applications including electronic, medical, dental, surface coating, and jewelry.

  10. Synthesis, structure and magnetism of new polynuclear transition metal aggregates assembled with Schiff-base ligand and anionic N-donor ligands

    NASA Astrophysics Data System (ADS)

    Li, Yangguang; Wu, Qiong; Lecren, Lollita; Clérac, Rodolphe

    2008-11-01

    Three new polynuclear aggregates [Co 6(sae) 4(N 3) 6(MeO) 2(MeOH) 2]·0.5H 2O ( 1), [Mn 4O(sae) 4(C(CN) 3)(MeOH) 3](NO 3)·MeOH ( 2) and [NaFe 6(sae) 6(MeO) 6] (N(CN) 2)·H 2O ( 3) have been synthesized with mixed ligands of Schiff-base (salicylidene-2-ethanolamine, H 2sae) and various anionic N-donor ligands (N 3-, N(CN) 2- or C(CN) 3-) and transition metal salts in methanol solution. Crystallographic data for 1: trigonal, R3¯, a = 26.113(4) Å, b = 26.113(4) Å, c = 20.689(4) Å, γ = 120°, V = 12,218(3) Å 3, Z = 9, R1( wR2) = 0.0753(0.2176); for 2: orthorhombic, Pna2 1, a = 20.746(4) Å, b = 13.357(3) Å, c = 17.992(4) Å, V = 4985.6(2) Å 3, Z = 4, R1( wR2) = 0.0357(0.0969); for 3: monoclinic, C2/ c, a = 30.311(6) Å, b = 12.452(3) Å, c = 20.789(4) Å, β = 94.75(3)°, V = 7820(3) Å 3, Z = 4, R1( wR2) = 0.0773(0.2299). Compound 1 exhibits a new rod-like [Co III4Co II2] structural feature. Compound 2 contains an unusual tetranuclear [Mn III4] cationic core. Compound 3 possesses a well-known circle-like [Fe III6] unit encapsulated a central sodium cation. Magnetic properties of these compounds have been studied revealing the presence of (i) intra-molecular antiferromagnetic interactions in 2 and 3 that induce an overall ST = 0 ground state and (ii) Co II-Co II ferromagnetic interactions in complex 1.

  11. Structural, photophysical and magnetic properties of transition metal complexes based on the dipicolylamino-chloro-1,2,4,5-tetrazine ligand.

    PubMed

    Nazarenko, Iuliia; Pop, Flavia; Sun, Qinchao; Hauser, Andreas; Lloret, Francesc; Julve, Miguel; El-Ghayoury, Abdelkrim; Avarvari, Narcis

    2015-05-21

    The ligand 3-chloro-6-dipicolylamino-1,2,4,5-tetrazine (Cl-TTZ-dipica) , prepared by the direct reaction between 3,6-dichloro-1,2,4,5-tetrazine and di(2-picolyl)-amine, afforded a series of four neutral transition metal complexes formulated as [Cl-TTZ-dipica-MCl2]2, with M = Zn(II), Cd(II), Mn(II) and Co(II), when reacted with the corresponding metal chlorides. The dinuclear structure of the isostructural complexes was disclosed by single crystal X-ray analysis, clearly indicating the formation of [M(II)-(μ-Cl)2M(II)] motifs and the involvement of the amino nitrogen atom in semi-coordination with the metal centers, thus leading to distorted octahedral coordination geometries. Moreover, the chlorine atoms, either coordinated to the metal or as a substituent on the tetrazine ring, engage respectively in specific anion-π intramolecular and intermolecular interactions with the electron-poor tetrazine units in the solid state, thus controlling the supramolecular architecture. Modulation of the emission properties is observed in the case of the Zn(II) and Cd(II) complexes when compared to the free ligand. A striking difference is observed in the magnetic properties of the Mn(II) and Co(II) complexes. An antiferromagnetic coupling takes place in the dimanganese(II) compound (J = -1.25 cm(-1)) while the Co(II) centers are ferromagnetically coupled in the corresponding complex (J = +0.55 cm(-1)), the spin Hamiltonian being defined as H = -JSA·SB. PMID:25868861

  12. Electrolytic separation of crystals of transition-metal oxides

    NASA Technical Reports Server (NTRS)

    Arnott, R. J.; Feretti, A.; Kunnamann, W.

    1969-01-01

    Versatile flux system grows large, well-formed, stoichiometric single crystals of mixed oxides of the transition-metal elements. These crystals have important uses in the microwave field, and applications as lasers and masers in communications.

  13. Electrical properties of transition metal hydrogen complexes in silicon

    SciTech Connect

    Weber, J.

    1998-12-31

    A summary is given on the electrical properties of transition-metal hydrogen complexes in silicon. Contrary to the general understanding, hydrogen leads not only to passivation of deep defect levels but also creates several new levels in the band gap due to electrically active transition-metal complexes. The author presents detailed data for Pt-H complexes and summarize briefly the results on the transition metals Ti, Co, Ni, Pd, and Ag. The introduction of hydrogen at room temperature by wet chemical etching, followed by specific annealing steps allows us to study the formation of the different complexes. In particular, depth profiles of the defect concentrations give an estimate of the number of hydrogen atoms involved in the complexes. Transition-metals binding up to four hydrogen atoms are identified.

  14. Mechanisms of transition-metal gettering in silicon

    SciTech Connect

    MYERS JR.,SAMUEL M.; SEIBT,M.; SCHROTER,W.

    2000-03-23

    The atomic process, kinetics, and equilibrium thermodynamics underlying the gettering of transition-metal impurities in Si are reviewed from a mechanistic perspective. Methods for mathematical modeling of gettering are reviewed and illustrated. Needs for further research are discussed.

  15. Design, spectral characterization, DFT and biological studies of transition metal complexes of Schiff base derived from 2-aminobenzamide, pyrrole and furan aldehyde

    NASA Astrophysics Data System (ADS)

    Tyagi, Prateek; Chandra, Sulekh; Saraswat, B. S.; Sharma, Deepansh

    2015-05-01

    A series of two biologically active Schiff base ligands L1, L2 have been synthesized in equimolar reaction of 2-aminobenzamide with pyrrol-2-carboxaldehyde and furan-2-carboxaldehyde. The synthesized Schiff bases were used for complexation with different metal ions like Co(II), Ni(II) and Cu(II) by using a molar ratio of ligand: metal as 2:1. The characterization of newly formed complexes was done by 1H NMR, UV-Vis, TGA, IR, mass spectrophotometry, EPR and molar conductivity studies. The thermal studies suggested that the complexes are more stable as compared to ligand. In DFT studies the geometries of Schiff bases and metal complexes were fully optimized with respect to the energy using the 6-31+g(d,p) basis set. On the basis of the spectral studies an octahedral geometry has been assigned for Co(II) and Ni(II) complexes and distorted octahedral geometry for Cu(II) complexes. All the synthesized compounds, were studied for their in vitro antimicrobial activities, against four bacterial strains and two fungal strains by using serial dilution method. The data also revealed that the metal complexes showed better activity than the ligands due to chelation/coordination.

  16. Design, spectral characterization, DFT and biological studies of transition metal complexes of Schiff base derived from 2-aminobenzamide, pyrrole and furan aldehyde.

    PubMed

    Tyagi, Prateek; Chandra, Sulekh; Saraswat, B S; Sharma, Deepansh

    2015-05-15

    A series of two biologically active Schiff base ligands L(1), L(2) have been synthesized in equimolar reaction of 2-aminobenzamide with pyrrol-2-carboxaldehyde and furan-2-carboxaldehyde. The synthesized Schiff bases were used for complexation with different metal ions like Co(II), Ni(II) and Cu(II) by using a molar ratio of ligand: metal as 2:1. The characterization of newly formed complexes was done by (1)H NMR, UV-Vis, TGA, IR, mass spectrophotometry, EPR and molar conductivity studies. The thermal studies suggested that the complexes are more stable as compared to ligand. In DFT studies the geometries of Schiff bases and metal complexes were fully optimized with respect to the energy using the 6-31+g(d,p) basis set. On the basis of the spectral studies an octahedral geometry has been assigned for Co(II) and Ni(II) complexes and distorted octahedral geometry for Cu(II) complexes. All the synthesized compounds, were studied for their in vitro antimicrobial activities, against four bacterial strains and two fungal strains by using serial dilution method. The data also revealed that the metal complexes showed better activity than the ligands due to chelation/coordination. PMID:25706679

  17. The transition to the metallic state in low density hydrogen.

    PubMed

    McMinis, Jeremy; Morales, Miguel A; Ceperley, David M; Kim, Jeongnim

    2015-11-21

    Solid atomic hydrogen is one of the simplest systems to undergo a metal-insulator transition. Near the transition, the electronic degrees of freedom become strongly correlated and their description provides a difficult challenge for theoretical methods. As a result, the order and density of the phase transition are still subject to debate. In this work, we use diffusion quantum Monte Carlo to benchmark the transition between paramagnetic and anti-ferromagnetic body centered cubic atomic hydrogen in its ground state. We locate the density of the transition by computing the equation of state for these two phases and identify the phase transition order by computing the band gap near the phase transition. These benchmark results show that the phase transition is continuous and occurs at a Wigner-Seitz radius of rs = 2.27(3) a0. We compare our results to previously reported density functional theory, Hedin's GW approximation, and dynamical mean field theory results. PMID:26590549

  18. Synthesis, spectroscopic studies and inhibitory activity against bactria and fungi of acyclic and macrocyclic transition metal complexes containing a triamine coumarine Schiff base ligand

    NASA Astrophysics Data System (ADS)

    Abou-Hussein, A. A.; Linert, Wolfgang

    2015-04-01

    Two series of new mono and binuclear complexes with a Schiff base ligand derived from the condensation of 3-acetylcoumarine and diethylenetriamine, in the molar ratio 2:1 have been prepared. The ligand was characterized by elemental analysis, IR, UV-visible, 1H-NMR and mass spectra. The reaction of the Schiff base ligand with cobalt(II), nickel(II), copper(II), zinc(II) and oxovanadium(IV) lead to mono or binuclear species of cyclic or macrocyclic complexes, depending on the mole ratio of metal to ligand and as well as on the method of preparation. The Schiff base ligand behaves as a cyclic bidentate, tetradendate or pentaentadentae ligand. The formation of macrocyclic complexes depends significantly on the dimension of the internal cavity, the rigidity of the macrocycles, the nature of its donor atoms and on the complexing properties of the anion involved in the coordination. Electronic spectra and magnetic moments of the complexes indicate that the geometries of the metal centers are either square pyramidal or octahedral for acyclic or macro-cyclic complexes. The structures are consistent with the IR, UV-visible, ESR, 1H-NMR, mass spectra as well as conductivity and magnetic moment measurements. The Schiff base ligand and its metal complexes were tested against two pathogenic bacteria as Gram-positive and Gram-negative bacteria as well as one kind of fungi. Most of the complexes exhibit mild antibacterial and antifungal activities against these organisms.

  19. Magnetization of ternary alloys based on Fe0.65Ni0.35 invar with 3d transition metal additions: An ab initio study

    NASA Astrophysics Data System (ADS)

    Onoue, Masatoshi; Trimarchi, Giancarlo; Freeman, Arthur J.; Popescu, Voicu; Matsen, Marc R.

    2015-01-01

    Smart susceptors are being developed for use as tooling surfaces in molding machines that use apply electro-magnetic induction heating to mold and form plastics or metal powders into structural parts, e.g., on aerospace and automotive manufacturing lines. The optimal magnetic materials for the induction heating process should have large magnetization, high magnetic permeability, but also small thermal expansion coefficient. The Fe0.65Ni0.35 invar alloy with its negligible thermal expansion coefficient is thus a natural choice for this application. Here, we use density functional theory as implemented through the Korringa-Kohn-Rostoker method within the coherent-potential approximation, to design new alloys with the large magnetization desired for smart susceptor applications. We consider the Fe0.65-xNi0.35-yMx+y alloys derived from Fe0.65Ni0.35 invar adding a third element M = Sc, Ti, V, Cr, Mn, or Co with concentration (x + y) reaching up to 5 at. %. We find that the total magnetization depends linearly on the concentration of M. Specifically, the early 3d transition metals from Sc to Cr decrease the magnetization with respect to that of the invar alloy whereas Mn and Co increase it.

  20. [Non-empirical interatomic potentials for transition metals

    SciTech Connect

    Not Available

    1993-01-01

    The report is divided into the following sections: potential-energy functions for d-band metals, potential-energy functions for aluminides and quasicrystals, electronic structure of complex structures and quasicrystals, potential-energy functions in transition-metal oxides, applications to defect structure and mechanical properties, and basic theory of interatomic potentials.

  1. [Non-empirical interatomic potentials for transition metals]. Progress report

    SciTech Connect

    Not Available

    1993-05-01

    The report is divided into the following sections: potential-energy functions for d-band metals, potential-energy functions for aluminides and quasicrystals, electronic structure of complex structures and quasicrystals, potential-energy functions in transition-metal oxides, applications to defect structure and mechanical properties, and basic theory of interatomic potentials.

  2. Configuring bonds between first-row transition metals.

    PubMed

    Eisenhart, Reed J; Clouston, Laura J; Lu, Connie C

    2015-11-17

    Alfred Werner, who pioneered the field of coordination chemistry, envisioned coordination complexes as a single, transition metal atom at the epicenter of a vast ligand space. The idea that the locus of a coordination complex could be shared by multiple metals held together with covalent bonds would eventually lead to the discovery of the quadruple and quintuple bond, which have no analogues outside of the transition metal block. Metal-metal bonding can be classified into homometallic and heterometallic groups. Although the former is dominant, the latter is arguably more intriguing because of the inherently larger chemical space in which metal-metal bonding can be explored. In 2013, Lu and Thomas independently reported the isolation of heterometallic multiple bonds with exclusively first-row transition metals. Structural and theoretical data supported triply bonded Fe-Cr and Fe-V cores. This Account describes our continued efforts to configure bonds between first-row transition metals from titanium to copper. Double-decker ligands, or binucleating platforms that brace two transition metals in proximity, have enabled the modular synthesis of diverse metal-metal complexes. The resulting complexes are also ideal for investigating the effects of an "ancillary" metal on the properties and reactivities of an "active" metal center. A total of 38 bimetallic complexes have been compiled comprising 18 unique metal-metal pairings. Twenty-one of these bimetallics are strictly isostructural, allowing for a systematic comparison of metal-metal bonding. The nature of the chemical bond between first-row metals is remarkably variable and depends on two primary factors: the total d-electron count, and the metals' relative d-orbital energies. Showcasing the range of covalent bonding are a quintuply bonded (d-d)(10) Mn-Cr heterobimetallic and the singly bonded late-late pairings, e.g., Fe-Co, which adopt unusually high spin states. A long-term goal is to rationally tailor the

  3. Exfoliation of large-area transition metal chalcogenide single layers

    PubMed Central

    Magda, Gábor Zsolt; Pető, János; Dobrik, Gergely; Hwang, Chanyong; Biró, László P.; Tapasztó, Levente

    2015-01-01

    Isolating large-areas of atomically thin transition metal chalcogenide crystals is an important but challenging task. The mechanical exfoliation technique can provide single layers of the highest structural quality, enabling to study their pristine properties and ultimate device performance. However, a major drawback of the technique is the low yield and small (typically < 10 μm) lateral size of the produced single layers. Here, we report a novel mechanical exfoliation technique, based on chemically enhanced adhesion, yielding MoS2 single layers with typical lateral sizes of several hundreds of microns. The idea is to exploit the chemical affinity of the sulfur atoms that can bind more strongly to a gold surface than the neighboring layers of the bulk MoS2 crystal. Moreover, we found that our exfoliation process is not specific to MoS2, but can be generally applied for various layered chalcogenides including selenites and tellurides, providing an easy access to large-area 2D crystals for the whole class of layered transition metal chalcogenides. PMID:26443185

  4. Magnetism In 3d Transition Metals at High Pressures

    SciTech Connect

    Iota, V

    2006-02-09

    This research project examined the changes in electronic and magnetic properties of transition metals and oxides under applied pressures, focusing on complex relationship between magnetism and phase stability in these correlated electron systems. As part of this LDRD project, we developed new measurement techniques and adapted synchrotron-based electronic and magnetic measurements for use in the diamond anvil cell. We have performed state-of-the-art X-ray spectroscopy experiments at the dedicated high-pressure beamline HP-CAT (Sector 16 Advanced Photon Source, Argonne National Laboratory), maintained in collaboration with of University of Nevada, Las Vegas and Geophysical Laboratory of The Carnegie Institution of Washington. Using these advanced measurements, we determined the evolution of the magnetic order in the ferromagnetic 3d transition metals (Fe, Co and Ni) under pressure, and found that at high densities, 3d band broadening results in diminished long range magnetic coupling. Our experiments have allowed us to paint a unified picture of the effects of pressure on the evolution of magnetic spin in 3d electron systems. The technical and scientific advances made during this LDRD project have been reported at a number of scientific meetings and conferences, and have been submitted for publication in technical journals. Both the technical advances and the physical understanding of correlated systems derived from this LDRD are being applied to research on the 4f and 5f electron systems under pressure.

  5. Chemical Trends for Transition Metal Compound Bonding to Graphene

    NASA Astrophysics Data System (ADS)

    Lange, Bjoern; Blum, Volker

    2015-03-01

    Transition metal compounds are of interest as catalysts for the hydrogen evolution reaction (HER). However, a perfect candidate to replace expensive platinum has not yet been identified. To tailor a specific compound, several properties come into play. One is the bonding to the underlying substrate, for which π-bonded carbon nanostructures are promising candidates. Here we analyze the bonding of small transition metal compound nanoclusters to a graphene layer for a range of chemical compositions: MxAy (M = Mo, Ti; A = S, O, B, N, C). The clusters are generated by an unbiased random search algorithm. We perform total energy calculations based on density functional theory to identify lowest energy clusters. We calculate binding energies using the PBE and HSE functionals with explicit van der Waals treatment and benchmark those against RPA cluster calculations. Our results indicate that molybdenum-carbides and -nitrides tend to bond tightly to graphene. Mo-oxides and -sulfides show small binding energies, indicating van der Waals bonding.

  6. Anderson metal-insulator transitions with classical magnetic impurities

    SciTech Connect

    Jung, Daniel; Kettemann, Stefan

    2014-08-20

    We study the effects of classical magnetic impurities on the Anderson metal-insulator transition (AMIT) numerically. In particular we find that while a finite concentration of Ising impurities lowers the critical value of the site-diagonal disorder amplitude W{sub c}, in the presence of Heisenberg impurities, W{sub c} is first increased with increasing exchange coupling strength J due to time-reversal symmetry breaking. The resulting scaling with J is compared to analytical predictions by Wegner [1]. The results are obtained numerically, based on a finite-size scaling procedure for the typical density of states [2], which is the geometric average of the local density of states. The latter can efficiently be calculated using the kernel polynomial method [3]. Although still suffering from methodical shortcomings, our method proves to deliver results close to established results for the orthogonal symmetry class [4]. We extend previous approaches [5] by combining the KPM with a finite-size scaling analysis. We also discuss the relevance of our findings for systems like phosphor-doped silicon (Si:P), which are known to exhibit a quantum phase transition from metal to insulator driven by the interplay of both interaction and disorder, accompanied by the presence of a finite concentration of magnetic moments [6].

  7. Anderson metal-insulator transitions with classical magnetic impurities

    NASA Astrophysics Data System (ADS)

    Jung, Daniel; Kettemann, Stefan

    2014-08-01

    We study the effects of classical magnetic impurities on the Anderson metal-insulator transition (AMIT) numerically. In particular we find that while a finite concentration of Ising impurities lowers the critical value of the site-diagonal disorder amplitude Wc, in the presence of Heisenberg impurities, Wc is first increased with increasing exchange coupling strength J due to time-reversal symmetry breaking. The resulting scaling with J is compared to analytical predictions by Wegner [1]. The results are obtained numerically, based on a finite-size scaling procedure for the typical density of states [2], which is the geometric average of the local density of states. The latter can efficiently be calculated using the kernel polynomial method [3]. Although still suffering from methodical shortcomings, our method proves to deliver results close to established results for the orthogonal symmetry class [4]. We extend previous approaches [5] by combining the KPM with a finite-size scaling analysis. We also discuss the relevance of our findings for systems like phosphor-doped silicon (Si:P), which are known to exhibit a quantum phase transition from metal to insulator driven by the interplay of both interaction and disorder, accompanied by the presence of a finite concentration of magnetic moments [6].

  8. Ab initio tight-binding Hamiltonian for transition metal dichalcogenides

    NASA Astrophysics Data System (ADS)

    Fang, Shiang; Kuate Defo, Rodrick; Shirodkar, Sharmila N.; Lieu, Simon; Tritsaris, Georgios A.; Kaxiras, Efthimios

    2015-11-01

    We present an accurate ab initio tight-binding Hamiltonian for the transition metal dichalcogenides, MoS2, MoSe2, WS2, WSe2, with a minimal basis (the d orbitals for the metal atoms and p orbitals for the chalcogen atoms) based on a transformation of the Kohn-Sham density functional theory Hamiltonian to a basis of maximally localized Wannier functions. The truncated tight-binding Hamiltonian, with only on-site, first, and partial second neighbor interactions, including spin-orbit coupling, provides a simple physical picture and the symmetry of the main band-structure features. Interlayer interactions between adjacent layers are modeled by transferable hopping terms between the chalcogen p orbitals. The full-range tight-binding Hamiltonian can be reduced to hybrid-orbital k .p effective Hamiltonians near the band extrema that capture important low-energy excitations. These ab initio Hamiltonians can serve as the starting point for applications to interacting many-body physics including optical transitions and Berry curvature of bands, of which we give some examples.

  9. The metal-insulator transition in vanadium dioxide nanobeams

    NASA Astrophysics Data System (ADS)

    Cobden, David

    2009-05-01

    Solid materials in which electron-electron correlations are strong can exhibit dramatic phase transitions, at which an abrupt change in the electronic properties occurs with a small accompanying distortion of the lattice. Such transitions could be harnessed to make electronic or optoelectronic devices or sensors embodying different principles from those in present semiconductor technology. A famous example is the metal-insulator transition in vanadium dioxide which occurs at 67 ^oC at ambient pressure. VO2 is a stable, strong material with a simple structure. Unfortunately though, applications and methodical studies of this and other phase transitions are hindered by broadening, hysteresis and mechanical degradation at the transition, caused by the inevitable domain structure. Nanostructures of the material which are smaller than the characteristic domain size do not show these problems. Using devices made from nanobeams of VO2 we have been able to achieve good control of the transition and to determine a number of its properties for the first time. For instance, we find that the metallic phase can be supercooled by more than 50 ^oC; that the resistivity of the insulator in coexistence with the metal is independent of temperature; and that the transition occurs via the intermediate M2 phase. We also study nanoelectromechanical effects where reversible buckling of the nanobeam is coupled to the phase transition, and we investigate methods of controlling the phase transition, for example using a gate voltage.

  10. Dielectric breakdown and avalanches at nonequilibrium metal-insulator transitions.

    PubMed

    Shekhawat, Ashivni; Papanikolaou, Stefanos; Zapperi, Stefano; Sethna, James P

    2011-12-30

    Motivated by recent experiments on the finite temperature Mott transition in VO(2) films, we propose a classical coarse-grained dielectric breakdown model where each degree of freedom represents a nanograin which transitions from insulator to metal with increasing temperature and voltage at random thresholds due to quenched disorder. We describe the properties of the resulting nonequilibrium metal-insulator transition and explain the universal characteristics of the resistance jump distribution. We predict that by tuning voltage, another critical point is approached, which separates a phase of boltlike avalanches from percolationlike ones. PMID:22243320

  11. Trion formation dynamics in monolayer transition metal dichalcogenides

    NASA Astrophysics Data System (ADS)

    Singh, Akshay; Moody, Galan; Tran, Kha; Scott, Marie E.; Overbeck, Vincent; Berghäuser, Gunnar; Schaibley, John; Seifert, Edward J.; Pleskot, Dennis; Gabor, Nathaniel M.; Yan, Jiaqiang; Mandrus, David G.; Richter, Marten; Malic, Ermin; Xu, Xiaodong; Li, Xiaoqin

    2016-01-01

    We report charged exciton (trion) formation dynamics in doped monolayer transition metal dichalcogenides, specifically molybdenum diselenide (MoS e2 ), using resonant two-color pump-probe spectroscopy. When resonantly pumping the exciton transition, trions are generated on a picosecond time scale through exciton-electron interaction. As the pump energy is tuned from the high energy to low energy side of the inhomogeneously broadened exciton resonance, the trion formation time increases by ˜ 50 % . This feature can be explained by the existence of both localized and delocalized excitons in a disordered potential and suggests the existence of an exciton mobility edge in transition metal dichalcogenides.

  12. Trion formation dynamics in monolayer transition metal dichalcogenides

    DOE PAGESBeta

    Singh, Akashay; Moody, Galan; Schaibley, John R.; Yan, Jiaqiang; Mandrus, David G.; Xu, Xiaodong; Li, Xiaoqun; Tran, Kha; Scott, Marie E.; Overbeck, Vincent; et al

    2016-01-05

    Here, we report charged exciton (trion) formation dynamics in doped monolayer transition metal dichalcogenides, specifically molybdenum diselenide (MoSe2), using resonant two-color pump-probe spectroscopy. When resonantly pumping the exciton transition, trions are generated on a picosecond time scale through exciton-electron interaction. As the pump energy is tuned from the high energy to low energy side of the inhomogeneously broadened exciton resonance, the trion formation time increases by ~50%. This feature can be explained by the existence of both localized and delocalized excitons in a disordered potential and suggests the existence of an exciton mobility edge in transition metal dichalcogenides.

  13. Activation of methane by transition metal-substituted aluminophosphate molecular sieves

    DOEpatents

    Iton, Lennox E.; Maroni, Victor A.

    1991-01-01

    Aluminophosphate molecular sieves substituted with cobalt, manganese or iron and having the AlPO.sub.4 -34 or AlPO.sub.4 -5, or related AlPO.sub.4 structure activate methane starting at approximately 350.degree. C. Between 400.degree. and 500.degree. C. and at methane pressures .ltoreq.1 atmosphere the rate of methane conversion increases steadily with typical conversion efficiencies at 500.degree. C. approaching 50% and selectivity to the production of C.sub.2+ hydrocarbons approaching 100%. The activation mechanism is based on reduction of the transition metal(III) form of the molecular sieve to the transition metal(II) form with accompanying oxidative dehydrogenation of the methane. Reoxidation of the - transition metal(II) form to the transition metal(III) form can be done either chemically (e.g., using O.sub.2) or electrochemically.

  14. Exchange coupling in transition metal monoxides: Electronic structure calculations

    SciTech Connect

    Fischer, Guntram; Daene, Markus W; Ernst, Arthur; Bruno, Patrick; Lueders, Martin; Szotek, Zdzislawa; Temmerman, Walter M; Wolfam, Hergert

    2009-01-01

    An ab initio study of magnetic-exchange interactions in antiferromagnetic and strongly correlated 3d transition metal monoxides is presented. Their electronic structure is calculated using the local self-interaction correction approach, implemented within the Korringa-Kohn-Rostoker band-structure method, which is based on multiple scattering theory. The Heisenberg exchange constants are evaluated with the magnetic force theorem. Based on these the corresponding Neel temperatures TN and spin-wave dispersions are calculated. The Neel temperatures are obtained using mean-field approximation, random-phase approximation and Monte Carlo simulations. The pressure dependence of TN is investigated using exchange constants calculated for different lattice constants. All the calculated results are compared to experimental data.

  15. Binding of transition metals to S100 proteins.

    PubMed

    Gilston, Benjamin A; Skaar, Eric P; Chazin, Walter J

    2016-08-01

    The S100 proteins are a unique class of EF-hand Ca(2+) binding proteins distributed in a cell-specific, tissue-specific, and cell cycle-specific manner in humans and other vertebrates. These proteins are distinguished by their distinctive homodimeric structure, both intracellular and extracellular functions, and the ability to bind transition metals at the dimer interface. Here we summarize current knowledge of S100 protein binding of Zn(2+), Cu(2+) and Mn(2+) ions, focusing on binding affinities, conformational changes that arise from metal binding, and the roles of transition metal binding in S100 protein function. PMID:27430886

  16. Transit-Depth Metallicity Correlation: A Bayesian Approach

    NASA Astrophysics Data System (ADS)

    Sarkis, P.; Nehmé, C.

    2015-12-01

    A negative correlation was previously reported between the transit depth of Kepler's Q1-Q12 gas giant candidates and the stellar metallicity. In this present work, we revisit this correlation to better understand the role of the stellar metallicity in the formation of giant planets, in particular, to investigate the effect of the metallicity on the transit depth. We selected the 82 confirmed giant planets from the cumulative catalogue. This is the first large and homogenous sample of confirmed giant planets used to study this correlation. Such samples are suitable to perform robust statistical analysis. We present the first hierarchical Bayesian linear regression model to revise this correlation. The advantages of using a Bayesian framework are to incorporate measurement errors in the model and to quantify both the intrinsic scatter and the uncertainties on the parameters of the model. Our statistical analysis reveals no correlation between the transit depth of confirmed giant planets and the stellar metallicity.

  17. Conversion and displacement reaction types of transition metal compounds for sodium ion battery

    NASA Astrophysics Data System (ADS)

    Chen, Guo-Ying; Sun, Qian; Yue, Ji-Li; Shadike, Zulipiya; Yang, Yin; Ding, Fei; Sang, Lin; Fu, Zheng-Wen

    2015-06-01

    Transition metal compounds of FeSe and CuWO4 thin films have been successfully fabricated by using R.F. sputtering method. Although two kinds of transition metal compounds of FeSe and CuWO4 thin films can react with sodium electrochemically, they exhibit different electrochemical features. The nanosized metal Fe is highly dispersed into Na2Se matrix and metal Cu is extruded from Na2WO4 mixture after the FeSe/Na and CuWO4/Na cells are discharged, respectively. The conversion reaction mechanism between FeSe and Na2Se is proposed for the FeSe/Na cell. While the displacement reaction mechanism for CuWO4/Na cell is proposed for the first time based on the transmission electron microscopy (TEM) and selected area electron diffraction (SAED) data. These various mechanisms make transition metal compounds interesting materials for rechargeable sodium ion batteries.

  18. Transition Metal Substitution Effects on Metal-to-Polyoxometalate Charge Transfer.

    PubMed

    Glass, Elliot N; Fielden, John; Huang, Zhuangqun; Xiang, Xu; Musaev, Djamaladdin G; Lian, Tianquan; Hill, Craig L

    2016-05-01

    A series of hetero-bimetallic transition metal-substituted polyoxometalates (TMSPs) were synthesized based on the Co(II)-centered ligand [Co(II)W11O39](10-). The eight complex series, [Co(II)(M(x)OHy)W11O39]((12-x-y)-) (M(x)OHy = V(IV)O, Cr(III)(OH2), Mn(II)(OH2), Fe(III)(OH2), Co(II)(OH2), Ni(II)(OH2), Cu(II)(OH2), Zn(II)(OH2)), of which six are reported for the first time, was synthesized starting from [Co(III)W11O39](9-) and studied using spectroscopic, electrochemical, and computational techniques to evaluate the influence of substituted transition metals on the photodynamics of the metal-to-polyoxometalate charge transfer (MPCT) transition. The bimetallic complexes all show higher visible light absorption than the plenary [Co(II)W12O40](6-) and demonstrate the same MPCT transition as the plenary complex, but they have shorter excited-state lifetimes (sub-300 ps in aqueous media). The decreased lifetimes are rationalized on the basis of nonradiative relaxation due to coordinating aqua ligands, increased interaction with cations due to increased negative charge, and the energy gap law, with the strongest single factor appearing to be the charge on the anion. The most promising results are from the Cr- and Fe-substituted systems, which retain excited-state lifetimes at least 50% of that of [Co(II)W12O40](6-) while more than tripling the absorbance at 400 nm. PMID:27082443

  19. Transition Metals in Control of Gene Expression

    NASA Astrophysics Data System (ADS)

    O'Halloran, Thomas V.

    1993-08-01

    Metalloproteins play structural and catalytic roles in gene expression. The metalloregulatory proteins are a subclass that exerts metal-responsive control of genes involved in respiration, metabolism, and metal-specific homeostasis or stress-response systems, such as iron uptake and storage, copper efflux, and mercury detoxification. Two allosteric mechanisms for control of gene expression were first discovered in metalloregulatory systems: an iron-responsive translational control mechanism for ferritin production and a mercury-responsive DNA-distortion mechanism for transcriptional control of detoxification genes. These otherwise unrelated mechanisms give rise to a rapid physiological response when metal ion concentrations exceed a dangerous threshold. Molecular recognition in these allosteric metal ion receptors is achieved through atypical coordination geometries, cluster formation, or complexes with prosthetic groups, such as sulfide and heme. Thus, many of the inorganic assemblies that otherwise buttress the structure of biopolymers or catalyze substrate transformation in active sites of enzymes have also been adapted to serve sensor functions in the metalloregulatory proteins. Mechanistic studies of these metal-sensor protein interactions are providing new insights into fundamental aspects of inorganic chemistry, molecular biology, and cellular physiology.

  20. [Transition metal mediated transformations of small molecules

    SciTech Connect

    Sen, A.

    1992-01-01

    Work on organotransition metal chemistry, homogeneous and heterogeneous catalysis is summarized. Several cationic palladium(II) complexes with bulky phosphine or pyridine ligands were discovered that are highly selective catalysts for linear dimerization of vinyl monomers and linear polymerization of p-divinylbenzene, the reactions proceeding through a carbocationic mechanism. Our studies were continued on alternating olefin-carbon monoxide copolymers. The copolymerization reaction and reactivity of copolymers were examined. New catalytic systems for alternating copolymerization of [alpha]-olefins with CO were discovered. In the case of styrene derivatives, tactic copolymers were obtained. Poly(ethylenepyrrolediyl) derivatives were synthesized from alternating ethylene-carbon monoxide copolymer and become electronic conductors when doped with iodine. A catalytic system for direct synthesis of polyureas and polyoxamides from and diamines was also discovered. Pt metal catalyzed the oxidation of ethers, esters, and amines to carboxylic acids and the oxidation of olefins to 1,2-diols. Anaerobic and aerobic decomposition of molybdenum(VI)-oxoalkyl compounds were studied for heterogeneous oxidation of alkanes and olefins on Mo(VI)-oxide surfaces. Synthesis of polymer-trapped metal, metal oxide, and metal sulfide nanoclusters (size <1--10 nm) was studied.

  1. Flexible metallic seal for transition duct in turbine system

    SciTech Connect

    Flanagan, James Scott; LeBegue, Jeffrey Scott; McMahan, Kevin Weston; Dillard, Daniel Jackson; Pentecost, Ronnie Ray

    2014-04-22

    A turbine system is disclosed. In one embodiment, the turbine system includes a transition duct. The transition duct includes an inlet, an outlet, and a passage extending between the inlet and the outlet and defining a longitudinal axis, a radial axis, and a tangential axis. The outlet of the transition duct is offset from the inlet along the longitudinal axis and the tangential axis. The transition duct further includes an interface member for interfacing with a turbine section. The turbine system further includes a flexible metallic seal contacting the interface member to provide a seal between the interface member and the turbine section.

  2. The Metallicities of Stars with and without Transiting Planets

    NASA Astrophysics Data System (ADS)

    Buchhave, Lars A.; Latham, David W.

    2015-08-01

    Host star metallicities have been used to infer observational constraints on planet formation throughout the history of the exoplanet field. The giant planet metallicity correlation has now been widely accepted, but questions remain as to whether the metallicity correlation extends to the small terrestrial-sized planets. Here, we report metallicities for a sample of 518 stars in the Kepler field that have no detected transiting planets and compare their metallicity distribution to a sample of stars that hosts small planets ({R}p\\lt 1.7 {R}\\oplus ). Importantly, both samples have been analyzed in a homogeneous manner using the same set of tools (Stellar Parameters Classification tool). We find the average metallicity of the sample of stars without detected transiting planets to be {[{{m}}/{{H}}]}{SNTP,{dwarf}}=-0.02+/- 0.02 {dex} and the sample of stars hosting small planets to be {[{{m}}/{{H}}]}{STP}=-0.02+/- 0.02 {dex}. The average metallicities of the two samples are indistinguishable within the uncertainties, and the two-sample Kolmogorov-Smirnov test yields a p-value of 0.68 (0.41σ), indicating a failure to reject the null hypothesis that the two samples are drawn from the same parent population. We conclude that the homogeneous analysis of the data presented here supports the hypothesis that stars hosting small planets have a metallicity similar to stars with no known transiting planets in the same area of the sky.

  3. Universal transition state scaling relations for (de)hydrogenation over transition metals.

    PubMed

    Wang, S; Petzold, V; Tripkovic, V; Kleis, J; Howalt, J G; Skúlason, E; Fernández, E M; Hvolbæk, B; Jones, G; Toftelund, A; Falsig, H; Björketun, M; Studt, F; Abild-Pedersen, F; Rossmeisl, J; Nørskov, J K; Bligaard, T

    2011-12-14

    We analyse the transition state energies for 249 hydrogenation/dehydrogenation reactions of atoms and simple molecules over close-packed and stepped surfaces and nanoparticles of transition metals using Density Functional Theory. Linear energy scaling relations are observed for the transition state structures leading to transition state scaling relations for all the investigated reactions. With a suitable choice of reference systems the transition state scaling relations form a universality class that can be approximated with one single linear relation describing the entire range of reactions over all types of surfaces and nanoclusters. PMID:21996683

  4. The metal-insulator transition in magnetite.

    NASA Technical Reports Server (NTRS)

    Cullen, J. R.; Callen, E.

    1972-01-01

    We describe an electronic model for the low temperature transition in magnetite, in which the average number of electrons on a site is non-integral. The solution of the one-dimensional problem is reviewed, and the connection of the model with the Verwey ordering is discussed. Some of the implication of the three dimensional problem are discussed.

  5. Modified electronic population analysis for transition-metal complexes

    SciTech Connect

    Noell, J.O.

    1982-01-01

    A modification to the Mulliken electronic population analysis designed primarily for use on transition-metal systems is presented. All terms arising from the metal basis functions including diagonal terms are repartioned between the metal and the ligands. This reapportionment is an attempt to reflect more accurately the actual electron density in well-defined areas of space, which characterize the metal and the ligand. This modified analysis appears to yield more reasonable charge assignments than a conventional Mulliken analysis. The cost of the analysis is negligible in comparison with that of calculating the wave function.

  6. Electronic Transitions in f-electron Metals at High Pressures:

    SciTech Connect

    Yoo, C; Maddox, B; Lazicki, A; Iota, V; Klepeis, J P; McMahan, A

    2007-02-08

    This study was to investigate unusual phase transitions driven by electron correlation effects that occur in many f-band transition metals and are often accompanied by large volume changes: {approx}20% at the {delta}-{alpha} transition in Pu and 5-15% for analogous transitions in Ce, Pr, and Gd. The exact nature of these transitions has not been well understood, including the short-range correlation effects themselves, their relation to long-range crystalline order, the possible existence of remnants of the transitions in the liquid, the role of magnetic moments and order, the critical behavior, and dynamics of the transitions, among other issues. Many of these questions represent forefront physics challenges central to Stockpile materials and are also important in understanding the high-pressure behavior of other f- and d-band transition metal compounds including 3d-magnetic transition monoxide (TMO, TM=Mn, Fe, Co, Ni). The overarching goal of this study was, therefore, to understand the relationships between crystal structure and electronic structure of transition metals at high pressures, by using the nation's brightest third-generation synchrotron x-ray at the Advanced Photon Source (APS). Significant progresses have been made, including new discoveries of the Mott transition in MnO at 105 GPa and Kondo-like 4f-electron dehybridization and new developments of high-pressure resonance inelastic x-ray spectroscopy and x-ray emission spectroscopy. These scientific discoveries and technology developments provide new insights and enabling tools to understand scientific challenges in stockpile materials. The project has broader impacts in training two SEGRF graduate students and developing an university collaboration (funded through SSAAP).

  7. Memristor using a transition metal nitride insulator

    SciTech Connect

    Stevens, James E; Marinella, Matthew; Lohn, Andrew John

    2014-10-28

    Apparatus is disclosed in which at least one resistive switching element is interposed between at least a first and a second conducting electrode element. The resistive switching element comprises a metal oxynitride. A method for making such a resistive switching element is also disclosed.

  8. The Role of Carbon in Catalytically Stabilized Transition Metal Sulfides

    SciTech Connect

    Kelty,S.; Berhault, G.; Chianelli, R.

    2007-01-01

    Since WWII considerable progress has been made in understanding the basis for the activity and the selectivity of molybdenum and tungsten based hydrotreating catalysts. Recently, the focus of investigation has turned to the structure of the catalytically stabilized active catalyst. The surface of the catalytically stabilized MoS2 has been shown to be carbided with the formula MoSxCy under hydrotreating conditions. In this paper we review the basis for this finding and present new data extending the concept to the promoted TMS (transition metal sulfides) systems CoMoC and NiMoC. Freshly sulfided CoMoS and NiMoS catalyst have a strong tendency to form the carbided surface phases from any available carbon source.

  9. Dynamical mean-field theory for transition metal dioxide molecules

    NASA Astrophysics Data System (ADS)

    Lin, Nan; Zgid, Dominika; Marianetti, Chris; Reichman, David; Millis, Andrew

    2012-02-01

    The utility of the dynamical mean-field approximation in quantum chemistry is investigated in the context of transition metal dioxide molecules including TiO2 and CrO2. The choice of correlated orbitals and correlations to treat dynamically is discussed. The dynamical mean field solutions are compared to state of the art quantum chemical calculations. The dynamical mean-field method is found to capture about 50% of the total correlation energy, and to produce very good results for the d-level occupancies and magnetic moments. We also present the excitation spectrum in these molecules which is inaccessible in many wave-function based methods. Conceptual and technical difficulties will be outlined and discussed.

  10. Metal-semiconductor transition of graphene nanoribbons with different addends

    NASA Astrophysics Data System (ADS)

    Zhang, X. W.; Dai, B.; Liu, J. S.; Yang, G. W.

    2012-02-01

    Using a LCAO method, which is based on spinless sp3 scheme, we have studied the electronic properties of graphene nanoribbons with zigzag edges (ZGNRs) terminated partially by methylene groups. Metal-semiconductor transition is proved when the H atoms at both sides of ZGNRs are partially substituted by methylene groups. Furthermore, when one-third of H atoms are substituted and the distribution of methylenes is symmetric, the band gap comes to about 0.59 eV, which is the widest energy gap in this work. Otherwise, when the addends at both sides are of asymmetric distribution, a band gap of only 0.21 eV is obtained. These results suggest that the addends at the edge of ZGNRs play an important role in modifying the electronic properties.

  11. Non-noble metal based metallization systems

    NASA Technical Reports Server (NTRS)

    Garcia, A., III

    1983-01-01

    The results of efforts to produce a nonsilver metallization system for silicon photovoltaic cells are given. The system uses a metallization system based on molybdenum, tin, and titanium hydride. The initial work in this system was done using the MIDFILM process. The MIDFILM process attains a line resolution comparable to photoresist methods with a process related to screen printing. The surface to be processed is first coated with a thin layer of photopolymer material. Upon exposure to ultraviolet light through a suitable mask, the polymer in the non-pattern area crosslinks and becomes hard. The unexposed pattern areas remain tacky. The conductor material is then applied in the form of a dry mixture of metal which adheres to the tacky pattern area. The assemblage is then fired to ash the photopolymer and sinter the conductor powder.

  12. Transition-Metal-Free Synthesis of Homo- and Hetero-1,2,4-Triaryl Benzenes by an Unexpected Base-Promoted Dearylative Pathway.

    PubMed

    Rehan, Mohammad; Maity, Sanjay; Morya, Lalit Kumar; Pal, Kaushik; Ghorai, Prasanta

    2016-06-27

    An unprecedented approach for the synthesis of homo- and hetero-1,2,4-triaryl benzenes has been developed using a simple base-mediated reaction of either α-aryl cinnamyl alcohols or α,γ-di-aryl propanones. The salient feature of this strategy involves the sequential hydride transfer, regiospecific condensation, regiospecific dearylation, and aromatization under metal-free reaction conditions. The synthesis of unsymmetrically substituted triphenylenes by oxidative coupling of the synthesized 1,2,4-triaryl benzenes has also been demonstrated. PMID:27061117

  13. Multidimensional transition metal complexes based on 3-amino-1H-1,2,4-triazole-5-carboxylic acid: from discrete mononuclear complexes to layered materials.

    PubMed

    Liu, Bing; Fernandes, José A; Tomé, João P C; Paz, Filipe A Almeida; Cunha-Silva, Luís

    2015-01-01

    The synthesis and structural characterization of five transition metal complexes with different dimensionality and incorporating residues of 3-amino-1H-1,2,4-triazole-5-carboxylic acid (H2atrc) is reported: [Zn(Hatrc)2(H2O)] (1), [Mn(Hatrc)2(H2O)2]·2H2O (2), [Fe2(Hatrc)4(OH)2]·6H2O (3), [Cd(Hatrc)2(H2O)]n (4), and [Mn(atrc)(H2O)]n·nH2O (5). These materials could be prepared from solution (1-3), diffusion (4), or hydrothermal reactions (5) with various anions and L:M ratios. Structural details were revealed by single crystal X-ray diffraction. The discrete units composing compounds 1-3, the polymeric 1D chain of 4 and the 2D layer of 5 are further extended into 3D supramolecular architectures through the formation of hydrogen bonds. PMID:26198221

  14. Yield stress in metallic glasses: The jamming-unjamming transition studied through Monte Carlo simulations based on the activation-relaxation technique

    SciTech Connect

    Rodney, David; Schuh, Christopher A.

    2009-11-01

    A Monte Carlo approach allowing for stress control is employed to study the yield stress of a two-dimensional metallic glass in the limit of low temperatures and long (infinite) time scales. The elementary thermally activated events are determined using the activation-relaxation technique (ART). By tracking the minimum-energy state of the glass for various applied stresses, we find a well-defined jamming-unjamming transition at a yield stress about 30% lower than the steady-state flow stress obtained in conventional strain-controlled quasistatic simulations. ART is then used to determine the evolution of the distribution of thermally activated events in the glass microstructure both below and above the yield stress. We show that aging below the yield stress increases the stability of the glass, both thermodynamically (the internal potential energy decreases) and dynamically (the aged glass is surrounded by higher-energy barriers than the initial quenched configuration). In contrast, deformation above the yield stress brings the glass into a high internal potential energy state that is only marginally stable, being surrounded by a high density of low-energy barriers. The strong influence of deformation on the glass state is also evidenced by the microstructure polarization, revealed here through an asymmetry of the distribution of thermally activated inelastic strains in glasses after simple shear deformation.

  15. Cumulant Approximated Second-Order Perturbation Theory Based on the Density Matrix Renormalization Group for Transition Metal Complexes: A Benchmark Study.

    PubMed

    Phung, Quan Manh; Wouters, Sebastian; Pierloot, Kristine

    2016-09-13

    The complete active space second order perturbation theory (CASPT2) can be extended to larger active spaces by using the density matrix renormalization group (DMRG) as solver. Two variants are commonly used: the costly DMRG-CASPT2 with exact 4-particle reduced density matrix (4-RDM) and the cheaper DMRG-cu(4)-CASPT2 in which the 4-cumulant is discarded. To assess the accuracy and limitations of the latter variant DMRG-cu(4)-CASPT2 we study the spin state energetics of iron porphyrin Fe(P) and its model compound FeL2, a model for the active center of NiFe hydrogenase, and manganese-oxo porphyrin MnO(P)(+); a series of excited states of chromium hexacarbonyl Cr(CO)6; and the interconversion of two Cu2O2(2+) isomers. Our results clearly show that PT2 on top of DMRG is essential in order to obtain quantitative results for transition metal complexes. Good results were obtained with DMRG-cu(4)-CASPT2 as compared to full CASPT2 and DMRG-CASPT2 in calculations with small- and medium-sized active spaces. In calculations with large-sized active spaces (∼30 active orbitals), the performance of DMRG-cu(4)-CASPT2 is less impressive due to the errors originating from both the finite number of renormalized states m and the 4-RDM approximation. PMID:27547847

  16. Metallization and charge-transfer gap closure of transition-metal iodides under pressure

    SciTech Connect

    Chen, A. Li-Chung

    1993-05-01

    It is shown with resistivity and near-IR absorption measurements that NiI{sub 2}, CoI{sub 2}, and FeI{sub 2} metallize under pressure by closure of the charge-transfer energy gap at pressures of 17, 10, and 23 GPa, respectively, which is close to the antiferromagnetic-diamagnetic transition in NiI{sub 2} and CoI{sub 2}. Thus, the magnetic transitions probably are caused by the metallization; in NiI{sub 2} and CoI{sub 2}, the insulator-metal transitions are first order. Moessbauer and XRD data were also collected. Figs, 46 refs.

  17. Ammonia and hydrazine. Transition-metal-catalyzed hydroamination and metal-free catalyzed functionalization

    SciTech Connect

    Bertrand, Guy

    2012-06-29

    high temperatures and long reaction times. To address this issue, we have developed several new families of carbon- and boron-based ligands, which are even better donors. The corresponding metal complexes (particularly gold, rhodium, iridium, and ruthenium) of all these species will be tested in the Markovnikov and anti-Markovnikov hydroamination of alkynes, allenes, and also alkenes with ammonia and hydrazine. We will also develop metal-free catalytic processes for the functionalization of ammonia and hydrazine. By possessing both a lone pair of electrons and an accessible vacant orbital, singlet carbenes resemble and can mimic the chemical behavior of transition metals. Our preliminary results demonstrate that specially designed carbenes can split the N–H bond of ammonia by an initial nucleophilic activation that prevents the formation of Lewis acid-base adducts, which is the major hurdle for the transition metal catalyzed functionalization of NH3. The use of purely organic compounds as catalysts will eliminate the major drawbacks of transition-metal-catalysis technology, which are the excessive cost of metal complexes (metal + ligands) and in many cases the toxicity of the metal.

  18. Phase diagram of the ultrafast photoinduced insulator-metal transition in vanadium dioxide

    NASA Astrophysics Data System (ADS)

    Cocker, T. L.; Titova, L. V.; Fourmaux, S.; Holloway, G.; Bandulet, H.-C.; Brassard, D.; Kieffer, J.-C.; El Khakani, M. A.; Hegmann, F. A.

    2012-04-01

    We use time-resolved terahertz spectroscopy to probe the ultrafast dynamics of the insulator-metal phase transition induced by femtosecond laser pulses in a nanogranular vanadium dioxide (VO2) film. Based on the observed thresholds for characteristic transient terahertz dynamics, a phase diagram of critical pump fluence versus temperature for the insulator-metal phase transition in VO2 is established for the first time over a broad range of temperatures down to 17 K. We find that both Mott and Peierls mechanisms are present in the insulating state and that the photoinduced transition is nonthermal. We propose a critical-threshold model for the ultrafast photoinduced transition based on a critical density of electrons and a critical density of coherently excited phonons necessary for the structural transition to the metallic state. As a result, evidence is found at low temperatures for an intermediate metallic state wherein the Mott state is melted but the Peierls distortion remains intact, consistent with recent theoretical predictions. Finally, the observed terahertz conductivity dynamics above the photoinduced transition threshold reveal nucleation and growth of metallic nanodomains over picosecond time scales.

  19. Transition metal-substituted cobalt ferrite nanoparticles for biomedical applications.

    PubMed

    Sanpo, Noppakun; Berndt, Christopher C; Wen, Cuie; Wang, James

    2013-03-01

    Transition metals of copper, zinc, chromium and nickel were substituted into cobalt ferrite nanoparticles via a sol-gel route using citric acid as a chelating agent. The microstructure and elemental composition were characterized using scanning electron microscopy combined with energy-dispersive X-ray spectroscopy. Phase analysis of transition metal-substituted cobalt ferrite nanoparticles was performed via X-ray diffraction. Surface wettability was measured using the water contact angle technique. The surface roughness of all nanoparticles was measured using profilometry. Moreover, thermogravimetric analysis and differential scanning calorimetry were performed to determine the temperature at which the decomposition and oxidation of the chelating agents took place. Results indicated that the substitution of transition metals influences strongly the microstructure, crystal structure and antibacterial property of the cobalt ferrite nanoparticles. PMID:23137676

  20. Superhardness effect in transition-metal diborides films

    NASA Astrophysics Data System (ADS)

    Bazhin, A. I.; Goncharov, A. A.; Pogrebnyak, A. D.; Stupak, V. A.; Goncharova, S. A.

    2016-06-01

    The structure, composition, and properties of transition-metal diboride films have been studied. It was shown that they are characterized by a wide range of structural states, namely from amorphous-like to nanocrystalline with crystallite sizes of 1-50 nm. The characteristic peculiarity of the structure of film transition-metal diborides with high physical and mechanical properties is the formation of a nanocrystalline (columnar) structure with the growth texture in plane [00.1] and a nanocrystallite size of 20-50 nm. The element composition of a superhard highly textured film transition-metal diborides was studied by ion mass spectrometry and Auger electron spectroscopy. The overstoichiometry effect in nanocrystalline transitionmetal diboride films is explained. It was shown that this effect is related to the formation of an additional B⎯B covalent bond, which is realized at subgrain boundaries and leads to the appearance of superhardness in the formed coatings.

  1. Nanodisperse transition metal electrodes (NTME) for electrochemical cells

    DOEpatents

    Striebel, Kathryn A.; Wen, Shi-Jie

    2000-01-01

    Disclosed are transition metal electrodes for electrochemical cells using gel-state and solid-state polymers. The electrodes are suitable for use in primary and secondary cells. The electrodes (either negative electrode or positive electrode) are characterized by uniform dispersion of the transition metal at the nanoscale in the polymer. The transition metal moiety is structurally amorphous, so no capacity fade should occur due to lattice expansion/contraction mechanisms. The small grain size, amorphous structure and homogeneous distribution provide improved charge/discharge cycling performance, and a higher initial discharge rate capability. The cells can be cycled at high current densities, limited only by the electrolyte conductivity. A method of making the electrodes (positive and negative), and their usage in electrochemical cells are disclosed.

  2. Nanodisperse transition metal electrodes (NTME) for electrochemical cells

    SciTech Connect

    Striebel, Kathryn A.; Wen, Shi-Jie

    1998-12-01

    Disclosed are transition metal electrodes for electrochemical cells using gel-state and solid-state polymers. The electrodes are suitable for use in primary and secondary cells. The electrodes (either negative electrode or positive electrode) are characterized by uniform dispersion of the transition metal at the nanoscale in the polymer. The transition metal moiety is structurally amorphous, so no capacity fade should occur due to lattice expansion/contraction mechanisms. The small grain size, amorphous structure and homogeneous distribution provide improved charge/discharge cycling performance, and a higher initial discharge rate capability. The cells can be cycled at high current densities, limited only by the electrolyte conductivity. A method of making the electrodes (positive and negative), and their usage in electrochemical cells are disclosed.

  3. Anharmonic Vibrational Spectroscopy on Metal Transition Complexes

    NASA Astrophysics Data System (ADS)

    Latouche, Camille; Bloino, Julien; Barone, Vincenzo

    2014-06-01

    Advances in hardware performance and the availability of efficient and reliable computational models have made possible the application of computational spectroscopy to ever larger molecular systems. The systematic interpretation of experimental data and the full characterization of complex molecules can then be facilitated. Focusing on vibrational spectroscopy, several approaches have been proposed to simulate spectra beyond the double harmonic approximation, so that more details become available. However, a routine use of such tools requires the preliminary definition of a valid protocol with the most appropriate combination of electronic structure and nuclear calculation models. Several benchmark of anharmonic calculations frequency have been realized on organic molecules. Nevertheless, benchmarks of organometallics or inorganic metal complexes at this level are strongly lacking despite the interest of these systems due to their strong emission and vibrational properties. Herein we report the benchmark study realized with anharmonic calculations on simple metal complexes, along with some pilot applications on systems of direct technological or biological interest.

  4. Transition-Metal Doped Ceria Microspheres with Nanoporous Structures for CO Oxidation.

    PubMed

    Zhou, Lin; Li, Xiaoxiao; Yao, Ze; Chen, Zhuwen; Hong, Mei; Zhu, Rongshu; Liang, Yongye; Zhao, Jing

    2016-01-01

    Catalytic oxidation of carbon monoxide (CO) is of great importance in many different fields of industry. Until now it still remains challenging to use non-noble metal based catalysts to oxidize CO at low temperature. Herein, we report a new class of nanoporous, uniform, and transition metal-doped cerium (IV) oxide (ceria, CeO2) microsphere for CO oxidation catalysis. The porous and uniform microsphere is generated by sacrificed polymer template. Transition-metals, like Cu, Co, Ni, Mn and Fe, were doped into CeO2 microspheres. The combination of hierarchical structure and metal doping afford superior catalytic activities of the doped ceria microspheres, which could pave a new way to advanced non-precious metal based catalysts for CO oxidation. PMID:27030159

  5. Transition-Metal Doped Ceria Microspheres with Nanoporous Structures for CO Oxidation

    NASA Astrophysics Data System (ADS)

    Zhou, Lin; Li, Xiaoxiao; Yao, Ze; Chen, Zhuwen; Hong, Mei; Zhu, Rongshu; Liang, Yongye; Zhao, Jing

    2016-03-01

    Catalytic oxidation of carbon monoxide (CO) is of great importance in many different fields of industry. Until now it still remains challenging to use non-noble metal based catalysts to oxidize CO at low temperature. Herein, we report a new class of nanoporous, uniform, and transition metal-doped cerium (IV) oxide (ceria, CeO2) microsphere for CO oxidation catalysis. The porous and uniform microsphere is generated by sacrificed polymer template. Transition-metals, like Cu, Co, Ni, Mn and Fe, were doped into CeO2 microspheres. The combination of hierarchical structure and metal doping afford superior catalytic activities of the doped ceria microspheres, which could pave a new way to advanced non-precious metal based catalysts for CO oxidation.

  6. Transition-Metal Doped Ceria Microspheres with Nanoporous Structures for CO Oxidation

    PubMed Central

    Zhou, Lin; Li, Xiaoxiao; Yao, Ze; Chen, Zhuwen; Hong, Mei; Zhu, Rongshu; Liang, Yongye; Zhao, Jing

    2016-01-01

    Catalytic oxidation of carbon monoxide (CO) is of great importance in many different fields of industry. Until now it still remains challenging to use non-noble metal based catalysts to oxidize CO at low temperature. Herein, we report a new class of nanoporous, uniform, and transition metal-doped cerium (IV) oxide (ceria, CeO2) microsphere for CO oxidation catalysis. The porous and uniform microsphere is generated by sacrificed polymer template. Transition-metals, like Cu, Co, Ni, Mn and Fe, were doped into CeO2 microspheres. The combination of hierarchical structure and metal doping afford superior catalytic activities of the doped ceria microspheres, which could pave a new way to advanced non-precious metal based catalysts for CO oxidation. PMID:27030159

  7. Electronic, magnetic and topological properties of transition metal oxides

    NASA Astrophysics Data System (ADS)

    Quan, Yundi

    III in AgO. Another interesting aspect of transition metal oxides is their topological properties that are attracting much attention in recent years. The semi-Dirac point, first discovered by Pardo et al and later modeled by Banerjee et al, has linear dispersion along the diagonal and quadratic dispersion perpendicular to the diagonal. In this thesis, we revisit the tight-binding Hamiltonian proposed by Banerjee and extend it to include the effects of external magnetic field on the energy spectrum and topological properties. We also discuss the forms of effective model Hamiltonians that can generate non-zero Berry phase. First principles calculations have been successful in guiding the experimental search for high Tc superconductors, the most recent example being high Tc (203K) superconductor H 3S under pressure (200GPa). The superconductivity of H3S was first predicted by Duan et al using DFT combined with structure optimization algorithms and validated soon after. Though elemental hydrogen was predicted to metallize under pressure in 1930, it was not realized until recently that hydrogen based compounds rather than pure hydrogen atoms are better candidates for high Tc superconductors. In this thesis, we carried out first principle calculations to study the unusual van Hove singularities located near the Fermi level that lead to a sharp peak, and analyzed the hybridization between sulfur and hydrogen states by constructing a tight-binding model.

  8. Strong dependence of fluorescence quenching on the transition metal in layered transition metal dichalcogenide nanoflakes for nucleic acid detection.

    PubMed

    Loo, Adeline Huiling; Bonanni, Alessandra; Pumera, Martin

    2016-08-01

    In recent years, the application of transition metal dichalcogenides for the development of biosensors has been receiving widespread attention from researchers, as demonstrated by the surge in studies present in the field. While different transition metal dichalcogenide materials have been employed for the fabrication of fluorescent biosensors with superior performance, no research has been conducted to draw comparisons across materials containing different transition metals. Herein, the performance of MoS2 and WS2 nanoflakes for the fluorescence detection of nucleic acids is assessed. It is discovered that, at the optimal amount, MoS2 and WS2 nanoflakes exhibit a similar degree of fluorescence quenching, at 75% and 71% respectively. However, MoS2 nanoflakes have better performance in the areas of detection range and selectivity than WS2 nanoflakes. The detection range achieved with MoS2 nanoflakes is 9.60-366 nM while 13.3-143 nM with WS2 nanoflakes. In the context of selectivity, MoS2 nanoflakes display a signal difference of 97.8% between complementary and non-complementary DNA targets, whereas WS2 nanoflakes only exhibit 44.3%. Such research is highly beneficial as it delivers vital insights on how the performance of a fluorescent biosensor can be affected by the transition metal present. Furthermore, these insights can assist in the selection of suitable transition metal dichalcogenide materials for utilization in biosensor development. PMID:27241269

  9. Anderson localization effects near the Mott metal-insulator transition

    NASA Astrophysics Data System (ADS)

    Bragança, Helena; Aguiar, M. C. O.; Vučičević, J.; Tanasković, D.; Dobrosavljević, V.

    2015-09-01

    The interplay between Mott and Anderson routes to localization in disordered interacting systems gives rise to different transitions and transport regimes. Here, we investigate the phase diagram at finite temperatures using dynamical mean-field theory combined with typical medium theory, which is an effective theory of the Mott-Anderson metal-insulator transition. We mainly focus on the properties of the coexistence region associated with the Mott phase transition. For weak disorder, the coexistence region is found to be similar to that in the clean case. However, as we increase disorder, Anderson localization effects are responsible for shrinking the coexistence region, and at sufficiently strong disorder (approximately equal to twice the bare bandwidth) it drastically narrows, the critical temperature Tc abruptly goes to zero, and we observe a phase transition in the absence of a coexistence of the metallic and insulating phases. In this regime, the effects of interaction and disorder are found to be of comparable importance for charge localization.

  10. Covalent functionalization of monolayered transition metal dichalcogenides by phase engineering.

    PubMed

    Voiry, Damien; Goswami, Anandarup; Kappera, Rajesh; e Silva, Cecilia de Carvalho Castro; Kaplan, Daniel; Fujita, Takeshi; Chen, Mingwei; Asefa, Tewodros; Chhowalla, Manish

    2015-01-01

    Chemical functionalization of low-dimensional materials such as nanotubes, nanowires and graphene leads to profound changes in their properties and is essential for solubilizing them in common solvents. Covalent attachment of functional groups is generally achieved at defect sites, which facilitate electron transfer. Here, we describe a simple and general method for covalent functionalization of two-dimensional transition metal dichalcogenide nanosheets (MoS₂, WS₂ and MoSe₂), which does not rely on defect engineering. The functionalization reaction is instead facilitated by electron transfer between the electron-rich metallic 1T phase and an organohalide reactant, resulting in functional groups that are covalently attached to the chalcogen atoms of the transition metal dichalcogenide. The attachment of functional groups leads to dramatic changes in the optoelectronic properties of the material. For example, we show that it renders the metallic 1T phase semiconducting, and gives it strong and tunable photoluminescence and gate modulation in field-effect transistors. PMID:25515889

  11. Phase stability of transition metal dichalcogenide by competing ligand field stabilization and charge density wave

    NASA Astrophysics Data System (ADS)

    C, Santosh K.; Zhang, Chenxi; Hong, Suklyun; Wallace, Robert M.; Cho, Kyeongjae

    2015-09-01

    Transition metal dichalcogenides (TMDs) have been investigated extensively for potential application as device materials in recent years. TMDs are found to be stable in trigonal prismatic (H), octahedral (T), or distorted octahedral (Td) coordination of the transition metal. However, the detailed understanding of stabilities of TMDs in a particular phase is lacking. In this work, the detailed TMD phase stability using first-principles calculations based on density functional theory (DFT) has been investigated to clarify the mechanism of phase stabilities of TMDs, consistent with the experimental observation. Our results indicate that the phase stability of TMDs can be explained considering the relative strength of two competing mechanisms: ligand field stabilization of d-orbitals corresponding to transition metal coordination geometry, and charge density wave (CDW) instability accompanied by a periodic lattice distortion (PLD) causing the phase transition in particular TMDs.

  12. 2D crystals of transition metal dichalcogenide and their iontronic functionalities

    NASA Astrophysics Data System (ADS)

    Zhang, Y. J.; Yoshida, M.; Suzuki, R.; Iwasa, Y.

    2015-12-01

    2D crystals based on transition metal dichalcogenides (TMDs) provide a unique platform of novel physical properties and functionalities, including photoluminescence, laser, valleytronics, spintronics, piezoelectric devices, field effect transistors (FETs), and superconductivity. Among them, FET devices are extremely useful because of voltage-tunable carrier density and Fermi energy. In particular, high density charge accumulation in electric double layer transistor (EDLT), which is a FET device driven by ionic motions, is playing key roles for expanding the functionalities of TMD based 2D crystals. Here, we report several device concepts which were realized by introducing EDLTs in TMDs, taking the advantage of their extremely unique band structures and phase transition phenomena realized simply by thinning to the monolayer level. We address two kinds of TMDs based on group VI and group V transition metals, which basically yield semiconductors and metals, respectively. For each system, we first introduce peculiar characteristics of TMDs achieved by thinning the crystals, followed by the related FET functionalities.

  13. Metal-insulator transition near a superconducting state

    NASA Astrophysics Data System (ADS)

    Kaveh, M.; Mott, N. F.

    1992-03-01

    We show that when the metal-insulation transition occurs near a superconducting state it results in a different critical behavior from that of amorphous metals or uncompensated doped semiconductors. This difference results from the enhancement of the effective electron-electron interaction caused by fluctuations to the superconducting state. This explains the recent experiments of Micklitz and co-workers on amorphous superconducting mixtures Ga-Ar and Bi-Kr.

  14. GW calculations on post-transition-metal oxides

    NASA Astrophysics Data System (ADS)

    Kang, Youngho; Kang, Gijae; Nahm, Ho-Hyun; Cho, Seong-Ho; Park, Young Soo; Han, Seungwu

    2014-04-01

    In order to establish the reliable GW scheme that can be consistently applied to post-transition-metal oxides (post-TMOs), we carry out comprehensive GW calculations on electronic structures of ZnO, Ga2O3,In2O3, and SnO2, the four representative post-TMOs. Various levels of self-consistency (G0W0, GW0, and QPGW0) and different starting functionals (GGA, GGA + U, and hybrid functional) are tested and their influence on the resulting electronic structure is closely analyzed. It is found that the GW0 scheme with GGA + U as the initial functional turns out to give the best agreement with experiment, implying that describing the position of metal-d level precisely in the ground state plays a critical role for the accurate dielectric property and quasiparticle band gap. Nevertheless, the computation on ZnO still suffers from the shallow Zn-d level and we propose a modified approach (GW0+Ud) that additionally considers an effective Hubbard U term during GW0 iterations and thereby significantly improves the band gap. It is also shown that a GGA + U-based GW0(+Ud) scheme produces an accurate energy gap of crystalline InGaZnO4, implying that this can serve as a standard scheme that can be applied to general structures of post-TMOs.

  15. Synthesis, spectroscopic characterisation, DNA cleavage, superoxidase dismutase activity and antibacterial properties of some transition metal complexes of a novel bidentate Schiff base derived from isatin and 2-aminopyrimidine.

    PubMed

    Nitha, L P; Aswathy, R; Mathews, Niecy Elsa; Kumari, B Sindhu; Mohanan, K

    2014-01-24

    Complexes of manganese(II), cobalt(II), nickel(II), copper(II) and zinc(II) with a Schiff base, formed by the condensation of isatin with 2-aminopyrimidine have been synthesised and characterised through elemental analysis, molar conductance measurements, magnetic susceptibility, IR, UV-Vis, (1)HNMR, FAB mass and EPR spectral studies. The spectral data revealed that the ligand acts as neutral bidentate, coordinating to the metal ion through the carbonyl oxygen and azomethine nitrogen. Molar conductance values adequately support the electrolytic nature of the complexes. On the basis of the above observations the complexes have been formulated as [M(ISAP)2]X2, where M=Mn(II), Co(II), Ni(II), Cu(II) and Zn(II); X=Cl, OAc; ISAP=2-[N-indole-2-one]aminopyrimidine. The ligand and copper(II) complex were subjected to X-ray diffraction studies. The DNA cleavage study was monitored by gel electrophoresis method. The superoxide dismutase (SOD) mimetic activities of the ligand and the metal complexes were checked using NBT assay. The in vitro antibacterial activity of the synthesized compounds has been tested against gram negative and gram positive bacteria. PMID:24051284

  16. Synthesis, spectroscopic characterisation, DNA cleavage, superoxidase dismutase activity and antibacterial properties of some transition metal complexes of a novel bidentate Schiff base derived from isatin and 2-aminopyrimidine

    NASA Astrophysics Data System (ADS)

    Nitha, L. P.; Aswathy, R.; Mathews, Niecy Elsa; Sindhu kumari, B.; Mohanan, K.

    2014-01-01

    Complexes of manganese(II), cobalt(II), nickel(II), copper(II) and zinc(II) with a Schiff base, formed by the condensation of isatin with 2-aminopyrimidine have been synthesised and characterised through elemental analysis, molar conductance measurements, magnetic susceptibility, IR, UV-Vis, 1HNMR, FAB mass and EPR spectral studies. The spectral data revealed that the ligand acts as neutral bidentate, coordinating to the metal ion through the carbonyl oxygen and azomethine nitrogen. Molar conductance values adequately support the electrolytic nature of the complexes. On the basis of the above observations the complexes have been formulated as [M(ISAP)2]X2, where M = Mn(II), Co(II), Ni(II), Cu(II) and Zn(II); X = Cl, OAc; ISAP = 2-[N-indole-2-one]aminopyrimidine. The ligand and copper(II) complex were subjected to X-ray diffraction studies. The DNA cleavage study was monitored by gel electrophoresis method. The superoxide dismutase (SOD) mimetic activities of the ligand and the metal complexes were checked using NBT assay. The in vitro antibacterial activity of the synthesized compounds has been tested against gram negative and gram positive bacteria.

  17. Synthesis, characterization, and antipathogenic studies of some transition metal complexes with N,O-chelating Schiff's base ligand incorporating azo and sulfonamide Moieties

    NASA Astrophysics Data System (ADS)

    Alaghaz, Abdel-Nasser M. A.; Bayoumi, Hoda A.; Ammar, Yousry A.; Aldhlmani, Sharah A.

    2013-03-01

    Chromium(III), Manganese(II), Cobalt(II), nickel(II), copper(II) and cadmium(II) complexes of 4-[4-hydroxy-3-(phenyliminomethyl)-phenylazo]benzenesulfonamide, were prepared and characterized on the basis of elemental analyses, spectral, magnetic, molar conductance and thermal analysis. Square planar, tetrahedral and octahedral geometries have been assigned to the prepared complexes. Dimeric complexes are obtained with 2:2 molar ratio except chromium(III) complex is monomeric which is obtained with 1:1 molar ratios. The IR spectra of the prepared complexes were suggested that the Schiff base ligand(HL) behaves as a bi-dentate ligand through the azomethine nitrogen atom and phenolic oxygen atom. The crystal field splitting, Racah repulsion and nepheloauxetic parameters and determined from the electronic spectra of the complexes. Thermal studies suggest a mechanism for degradation of HL and its metal complexes as function of temperature supporting the chelation modes. Also, the activation thermodynamic parameters, such as ΔE*, ΔH*, ΔS* and ΔG* for the different thermal decomposition steps of HL and its metal complexes were calculated. The pathogenic activities of the synthesized compounds were tested in vitro against the sensitive organisms Staphylococcus aureus (RCMB010027), Staphylococcus epidermidis (RCMB010024) as Gram positive bacteria, Klebsiella pneumonia (RCMB 010093), Shigella flexneri (RCMB 0100542), as Gram negative bacteria and Aspergillus fumigates (RCMB 02564), Aspergillus clavatus (RCMB 02593) and Candida albicans (RCMB05035) as fungus strain, and the results are discussed.

  18. Spectroscopic investigations of new binuclear transition metal complexes of Schiff bases derived from 4,6-diacetylresorcinol and 3-amino-1-propanol or 1,3-diamino-propane

    NASA Astrophysics Data System (ADS)

    Emara, Adel A. A.; Saleh, Akila A.; Adly, Omima M. I.

    2007-11-01

    The bifunctional carbonyl compound; 4,6-diacetylresorcinol (DAR) serves as precursor for the formation of different Schiff base ligands, which are either di- or tetra-basic with two symmetrical sets of either O 2N or N 2O tridentate chelating sites. The condensation of 4,6-diacetylresorcinol with 3-amino-1-propanol (3-AP) or 1,3-diaminopropane (DAP), yields the corresponding hexadentate Schiff base ligands, abbreviated as H 4L a and H 2L b, respectively. The structures of these ligands were elucidated by elemental analyses, IR, mass, 1H NMR and electronic spectra. Reaction of the Schiff base ligands with copper(II), nickel(II), cobalt(II), zinc(II), cadmium(II), iron(III), chromium(III), vanadyl(IV) and uranyl(VI) ions in 1:2 molar ratio afforded the corresponding transition metal complexes. A variety of binuclear complexes for the metal complexes were obtained with the ligands in its di- or tetra-deprotonated forms. The structures of the newly prepared complexes were identified by elemental analyses, infrared, electronic, mass, 1H NMR and ESR spectra as well as magnetic susceptibility measurements and thermal gravimetric analysis (TGA). The bonding sites are the azomethine and amino nitrogen atoms, and phenolic and alcoholic oxygen atoms. The metal complexes exhibit different geometrical arrangements such as square planar, tetrahedral, square pyramid and octahedral arrangement.

  19. Directly Predicting Water Quality Criteria from Physicochemical Properties of Transition Metals

    PubMed Central

    Wang, Ying; Wu, Fengchang; Mu, Yunsong; Zeng, Eddy Y.; Meng, Wei; Zhao, Xiaoli; Giesy, John P.; Feng, Chenglian; Wang, Peifang; Liao, Haiqing; Chen, Cheng

    2016-01-01

    Transition metals are a group of elements widespread in aquatic environments that can be hazardous when concentrations exceeding threshold values. Due to insufficient data, criteria maximum concentrations (CMCs) of only seven transition metals for protecting aquatic life have been recommended by the USEPA. Hence, it is deemed necessary to develop empirical models for predicting the threshold values of water quality criteria (WQC) for other transition metals for which insufficient information on toxic potency is available. The present study established quantitative relationships between recommended CMCs and physicochemical parameters of seven transition metals, then used the developed relationships to predict CMCs for other transition metals. Seven of 26 physicochemical parameters examined were significantly correlated with the recommended CMCs. Based on this, five of the seven parameters were selected to construct a linear free energy model for predicting CMCs. The most relevant parameters were identified through principle component analysis, and the one with the best correlation with the recommended CMCs was a combination of covalent radius, ionic radius and electron density. Predicted values were largely consistent with their toxic potency values. The present study provides an alternative approach to develop screening threshold level for metals which have insufficient information to use traditional methods. PMID:26936420

  20. Directly Predicting Water Quality Criteria from Physicochemical Properties of Transition Metals.

    PubMed

    Wang, Ying; Wu, Fengchang; Mu, Yunsong; Zeng, Eddy Y; Meng, Wei; Zhao, Xiaoli; Giesy, John P; Feng, Chenglian; Wang, Peifang; Liao, Haiqing; Chen, Cheng

    2016-01-01

    Transition metals are a group of elements widespread in aquatic environments that can be hazardous when concentrations exceeding threshold values. Due to insufficient data, criteria maximum concentrations (CMCs) of only seven transition metals for protecting aquatic life have been recommended by the USEPA. Hence, it is deemed necessary to develop empirical models for predicting the threshold values of water quality criteria (WQC) for other transition metals for which insufficient information on toxic potency is available. The present study established quantitative relationships between recommended CMCs and physicochemical parameters of seven transition metals, then used the developed relationships to predict CMCs for other transition metals. Seven of 26 physicochemical parameters examined were significantly correlated with the recommended CMCs. Based on this, five of the seven parameters were selected to construct a linear free energy model for predicting CMCs. The most relevant parameters were identified through principle component analysis, and the one with the best correlation with the recommended CMCs was a combination of covalent radius, ionic radius and electron density. Predicted values were largely consistent with their toxic potency values. The present study provides an alternative approach to develop screening threshold level for metals which have insufficient information to use traditional methods. PMID:26936420

  1. Directly Predicting Water Quality Criteria from Physicochemical Properties of Transition Metals

    NASA Astrophysics Data System (ADS)

    Wang, Ying; Wu, Fengchang; Mu, Yunsong; Zeng, Eddy Y.; Meng, Wei; Zhao, Xiaoli; Giesy, John P.; Feng, Chenglian; Wang, Peifang; Liao, Haiqing; Chen, Cheng

    2016-03-01

    Transition metals are a group of elements widespread in aquatic environments that can be hazardous when concentrations exceeding threshold values. Due to insufficient data, criteria maximum concentrations (CMCs) of only seven transition metals for protecting aquatic life have been recommended by the USEPA. Hence, it is deemed necessary to develop empirical models for predicting the threshold values of water quality criteria (WQC) for other transition metals for which insufficient information on toxic potency is available. The present study established quantitative relationships between recommended CMCs and physicochemical parameters of seven transition metals, then used the developed relationships to predict CMCs for other transition metals. Seven of 26 physicochemical parameters examined were significantly correlated with the recommended CMCs. Based on this, five of the seven parameters were selected to construct a linear free energy model for predicting CMCs. The most relevant parameters were identified through principle component analysis, and the one with the best correlation with the recommended CMCs was a combination of covalent radius, ionic radius and electron density. Predicted values were largely consistent with their toxic potency values. The present study provides an alternative approach to develop screening threshold level for metals which have insufficient information to use traditional methods.

  2. Synthesis, spectroscopic studies, antimicrobial activities and antitumor of a new monodentate V-shaped Schiff base and its transition metal complexes

    NASA Astrophysics Data System (ADS)

    Ramadan, Ramadan M.; Abu Al-Nasr, Ahmad K.; Noureldeen, Amani F. H.

    2014-11-01

    Reaction of 4-aminoacetophenone and 4-bromobenzaldehyde in ethanol resulted in the formation of the monodentate V-shaped Schiff base (E)-1-(4-((4-bromo-benzylidene)amino)phenyl)ethanone (L). Interaction of L with different di- and trivalent metal ions revealed disubstituted derivatives. The ligand and its complexes were characterized by elemental analysis, mass, IR and NMR spectrometry. Biological activities of the ligand and complexes against the Escherchia coli and Staphylococcus aureus bacterias, and the two fungus Aspergillus flavus and Candida albicans were screened. The cytotoxicity of the compounds were checked as antitumor agents on liver carcinoma cell line (HepG2). They exhibited in vitro broad range of antitumor activities towards the cell line; the [ZnL2(H2O)2](NO3)2 complex was stronger antitumor towards HepG2 cell line as well as two breast cancer cell lines (MCF7 and T47D) relative to cis-platin.

  3. Synthesis and spectroscopic characterization of some transition metal complexes of a new hexadentate N 2S 2O 2 Schiff base ligand

    NASA Astrophysics Data System (ADS)

    Sarkar, Saikat; Dey, Kamalendu

    2005-11-01

    A novel interesting hexadentate dibasic N 2S 2O 2 donor Schiff base ligand, H4dcsalpte, was synthesized by the condensation of 3-formylsalicylic acid and 1,2-di( o-aminophenylthio)ethane and characterized. The reactions of the ligand with different metal(II/III)salts under varied reaction conditions afforded a series of metal complexes. The ligand, H4dcsalpte, behaves either as a dibasic or neutral hexadentate one, depending on the reaction conditions. Structural investigations on the ligand and their complexes have been made based on elemental analyses, molar conductance values, magnetic moment values, cryomagnetic and spectral (UV-vis, IR, 1H NMR, and Mössbauer) data. Based on magnetic susceptibility, Mössbauer and electronic spectral data the iron(III) complex [Fe III( H2dcsalpte)]ClO 4 ( 8), isolated in the present investigation, it is inferred that the spin states 5/2 and 1/2 are in equilibrium. Similarly a tri-iron(III) complex [Fe III3( H2dcsalpte)( H3dcsalpte)Cl 3]Cl 3 ( 7), isolated in this study, has been inferred to contain two iron(III) sites in tetrahedral environment and one in the octahedral environment. The aerial oxidation of an equimolar mixture of H4dcsalpte and Co(CH 3COO) 2·4H 2O in ethanol under reflux gave two products, [Co( H2dcsalpte)]CH 3COO ( 10) and [( Hbtcsaldm)Co( Hbvcsaldm)] ( 11), a cobalt(III) complex bound to two dissimilar tridentate NSO donor ligands formed as a result of the oxidative cleavage of the C sbnd S bond. In the complex 11, Hbtcsaldm stands for the dianion of the tridentate Schiff base ligand N-(2'-benzenethiol)-3-carboxysalicylaldimine and Hbvcsaldm stands for the mono anion of the tridentate Schiff base ligand N-(benzene-2'-S-vinyl)-3-carboxysalicylaldimine, both being formed as a result of the oxidative cleavage of H4dcsalpte.

  4. Measurements of Schottky barrier heights formed from metals and 2D transition metal dichalcogedides

    NASA Astrophysics Data System (ADS)

    Kim, Changsik; Moon, Inyong; Nam, Seunggeol; Cho, Yeonchoo; Shin, Hyeon-Jin; Park, Seongjun; Yoo, Won Jong

    Schottky barrier height (SBH) is an important parameter that needs to be considered for designing electronic devices. However, for two dimensional (2D) materials based devices, SBH control is limited by 2D structure induced quantum confinement and 2D surface induced Fermi level pinning. In this work, we explore differences in measuring SBH between 2D and 3D materials. Recently, low temperature I-V measurement has been reported to extract SBH based on thermionic emission equation for Schottky diode. However, 2D devices are not real Schottky diode in that both source and drain metal electrodes make Schottky contact. According to our experimental results, SBH extracted from linear slope of ln (I/T3/2) against 1/T show widely diverse values, dependent on applied voltage bias and tested temperature which affect carrier transport including tunneling or thermionic emission across the metal-2D material interface. In this work, we wish to demonstrate the method to determine SBH and Fermi level pinning which are attributed to 2D transition metal dichalcogedides, differently from conventional 3D materials. .

  5. Oxygen activation with transition metal complexes in aqueous solution

    SciTech Connect

    Bakac, Andreja

    2010-04-12

    Coordination to transition-metal complexes changes both the thermodynamics and kinetics of oxygen reduction. Some of the intermediates (superoxo, hydroperoxo, and oxo species) are close analogues of organic oxygen-centered radicals and peroxides (ROO{sm_bullet}, ROOH, and RO{sm_bullet}). Metal-based intermediates are typically less reactive, but more persistent, than organic radicals, which makes the two types of intermediates similarly effective in their reactions with various substrates. The self-exchange rate constant for hydrogen-atom transfer for the couples Cr{sub aq}OO{sup 2+}/Cr{sub aq}OOH{sup 2+} and L{sup 1}(H{sub 2}O)RhOO{sup 2+}/L{sup 1}(H{sub 2}O)RhOOH{sup 2+} was estimated to be 10{sup 1 {+-} 1} M{sup -1} s{sup -1}. The use of this value in the simplified Marcus equation for the Cr{sub aq}O{sup 2+}/Cr{sub aq}OOH{sup 2+} cross reaction provided an upper limit k{sub CrO,CrOH} {le} 10{sup (-2{+-}1)} M{sup -1} s{sup -1} for Cr{sub aq}O{sup 2+}/Cr{sub aq}OH{sup 2+} self-exchange. Even though superoxo complexes react very slowly in bimolecular self-reactions, extremely fast cross reactions with organic counterparts, i.e., acylperoxyl radicals, have been observed. Many of the intermediates generated by the interaction of O{sub 2} with reduced metal complexes can also be accessed by alternative routes, both thermal and photochemical.

  6. The Electronic Structure of Transition Metal Coated Fullerenes

    NASA Astrophysics Data System (ADS)

    Patton, David C.; Pederson, Mark R.; Kaxiras, Efthimios

    1998-03-01

    Clusters composed of fullerene molecules with an outer shell of transition metal atoms in the composition C_60M_62 (M being a transition metal) have been produced with laser vaporisation techniques(F. Tast, N. Malinowski, S. Frank, M. Heinebrodt, I.M.L. Billas, and T. P. Martin, Z. Phys D 40), 351 (1997).. We have studied several of these very large systems with a parallel version of the all-electron NRLMOL cluster code. Optimized geometries of the metal encased fullerenes C_60Ti_62 and C_60V_62 are presented along with their HOMO-LUMO gaps, electron affinities, ionization energies, and cohesive energies. We compare the stability of these clusters to relaxed met-car structures (e.g. Ti_8C_12) and to relaxed rocksalt metal-carbide fragments (TiC)n with n=8 and 32. In addition to metal-coated fullerenes we consider the possibility of a trilayered structure consisting of a small shell of metal atoms enclosed by a metal coated fullerene. The nature of bonding in these systems is analyzed by studying the electronic charge distributions.

  7. Chromospheric, transition layer and coronal emission of metal deficient stars

    NASA Technical Reports Server (NTRS)

    Boehm-Vitense, E.

    1982-01-01

    It is shown that while MgII k line emission decreases for metal deficient stars, the Ly alpha emission increases. The sum of chromospheric hydrogen and metallic emission appears to be independent of metal abundances. The total chromospheric energy loss is estimated to be 0.0004 F sub bol. The chromospheric energy input does not seem to decrease for increasing age. The transition layer emission is reduced for metal deficient stars, but it is not known whether the reduction is larger than can be explained by curve of growth effects only. Coronal X-ray emission was measured for 4 metal deficient stars. Within a 12 limit it could still be consistent with the emission of solar abundance stars.

  8. Growth of transition metals on cerium tungstate model catalyst layers.

    PubMed

    Skála, T; Tsud, N; Stetsovych, V; Mysliveček, J; Matolín, V

    2016-10-01

    Two model catalytic metal/oxide systems were investigated by photoelectron spectroscopy and scanning tunneling microscopy. The mixed-oxide support was a cerium tungstate epitaxial thin layer grown in situ on the W(1 1 0) single crystal. Active particles consisted of palladium and platinum 3D islands deposited on the tungstate surface at 300 K. Both metals were found to interact weakly with the oxide support and the original chemical state of both support and metals was mostly preserved. Electronic and morphological changes are discussed during the metal growth and after post-annealing at temperatures up to 700 K. Partial transition-metal coalescence and self-cleaning from the CO and carbon impurities were observed. PMID:27494195

  9. The Electrochemical Synthesis of Transition-Metal Acetylacetonates

    ERIC Educational Resources Information Center

    Long, S. R.; Browning, S. R.; Lagowski, J. J.

    2008-01-01

    The electrochemical synthesis of transition-metal acetylacetonates described here can form the basis of assisting in the transformation of an entry-level laboratory course into a research-like environment where all members of a class are working on the same problem, but where each member has a personal responsibility for the synthesis and…

  10. Transport properties of transition metal impurities on gold nanowires

    NASA Astrophysics Data System (ADS)

    Pontes, Renato B.; da Silva, Edison Z.; Fazzio, Adalberto; da Silva, Antônio J. R.

    2009-03-01

    Performing first principles density functional theory (DFT) we calculated the electronic and transport properties of a Au thin nanowire with transition metal atoms (Mn, Fe, Ni or Co) bridging the two sides of the Au nanowire. We will show that these systems have strong spin dependent transport properties and that the local symmetry can dramatically change them, leading to a significant spin polarized conductance. This spin dependent transport is also associated with the transition metal in the nanowire, in particular with the d-level positioning. Using Co, for example [1], when the symmetry permits the mixing between the wire s-orbitals with the transition metal d-states, there are interference effects that resemble Fano-like resonances with an anisotropy of 0.07 at the Fermi level. On the other hand, if this symmetry decouples such states, we simply have a sum of independent transmission channels and the calculated anisotropy was 0.23. The anisotropies for the other transition metals, as well as calculated transmittances for two Co impurities will also be presented [1] R. B. Pontes, E. Z. da Silva, A. Fazzio and Antônio J. R. da Silva, J. Am. Chem. Soc. 130 (30), 9897-903, 2008

  11. Mechanisms of transition-metal gettering in silicon

    SciTech Connect

    Myers, S. M.; Seibt, M.; Schroeter, W.

    2000-10-01

    The atomic process, kinetics, and equilibrium thermodynamics underlying the gettering of transition-metal impurities in Si are reviewed. Methods for mathematical modeling of gettering are discussed and illustrated. Needs for further research are considered. (c) 2000 American Institute of Physics.

  12. Hydroxyapatite substituted by transition metals: experiment and theory.

    PubMed

    Zilm, M E; Chen, L; Sharma, V; McDannald, A; Jain, M; Ramprasad, R; Wei, M

    2016-06-28

    Bioceramics are versatile materials for hard tissue engineering. Hydroxyapatite (HA) is a widely studied biomaterial for bone grafting and tissue engineering applications. The crystal structure of HA allows for a wide range of substitutions, which allows for tailoring materials properties. Transition metals and lanthanides are of interest since substitution in HA can result in magnetic properties. In this study, experimental results were compared to theoretical calculations of HA substituted with a transition metal. Calculation of a 10 atomic percent substitution of a transition metal ion Mn(2+), Fe(2+), and Co(2+) substituted HA samples lead to magnetic moments of 5, 4, and 3 Bohr magnetons, respectively. Hydroxyapatite substituted by transition metals (MHA) was fabricated through an ion exchange procedure and characterized with X-ray diffraction, Fourier transform infra-red spectroscopy (FTIR), X-ray photoelectron spectroscopy, and vibrating sample magnetometer, and results were compared to theoretical calculations. All the substitutions resulted in phase-pure M(2+)HA with lattice parameters and FTIR spectra in good agreement with calculations. Magnetic measurements revealed that the substitution of Mn(2+) has the greatest effect on the magnetic properties of HA followed by the substitution of Fe(2+) and then Co(2+). The present work underlines the power of synergistic theoretical-experimental work in guiding the rational design of materials. PMID:27264723

  13. Luminescent molecular rods - transition-metal alkynyl complexes.

    PubMed

    Yam, Vivian Wing-Wah; Wong, Keith Man-Chung

    2005-01-01

    A number of transition-metal complexes have been reported to exhibit rich luminescence, usually originating from phosphorescence. Such luminescence properties of the triplet excited state with a large Stoke's shift, long lifetime, high luminescence quantum yield as well as lower excitation energy, are envisaged to serve as an ideal candidate in the area of potential applications for chemosensors, dye-sensitized solar cells, flat panel displays, optics, new materials and biological sciences. Organic alkynes (poly-ynes), with extended or conjugatedπ-systems and rigid structure with linear geometry, have become a significant research area due to their novel electronic and physical properties and their potential applications in nanotechnology. Owing to the presence of unsaturated sp-hybridized carbon atoms, the alkynyl unit can serve as a versatile building block in the construction of alkynyl transition-metal complexes, not only throughσ-bonding but also viaπ-bonding interactions. By incorporation of linear alkynyl groups into luminescent transition-metal complexes, the alkynyl moiety with goodσ-donor,π-donor andπ-acceptor abilities is envisaged to tune or perturb the emission behaviors, including emission energy (color), intensity and lifetime by its role as an auxiliary ligand as well as to govern the emission origin from its direct involvement. This review summarizes recent efforts on the synthesis of luminescent rod-like alkynyl complexes with different classes of transition metals and details the effects of the introduction of alkynyl groups on the luminescence properties of the complexes. PMID:22179333

  14. Stable singlet carbenes as mimics for transition metal centers

    PubMed Central

    Martin, David; Soleilhavoup, Michele

    2011-01-01

    This perspective summarizes recent results, which demonstrate that stable carbenes can activate small molecules (CO, H2, NH3 and P4) and stabilize highly reactive intermediates (main group elements in the zero oxidation state and paramagnetic species). These two tasks were previously exclusive for transition metal complexes. PMID:21743834

  15. Spin induced ferroelectric-like structural transition in a metal

    NASA Astrophysics Data System (ADS)

    Guo, Yanfeng; Feng, Hai; Andrew, Princep; Manuel, Pascal; Yamaura, Kazunari; Andrew, Boothroyd

    2015-03-01

    LiOsO3 represents a previously only known example of ``ferroelectric metal,'' a concept presented by Anderson and Blount in 1965, with the properties being promoted by electron lattice coupling involving Li+ ions displacement in the crystal structure [Y. Shi et al., Nat. Mater. 12, 1024(2013)]. We report that in Pb2CoOsO6, a new ordered double-perovskite with a centrosymmetric monoclinic space group of P21/n, a ferroelectric-like structural transition occurs at ~ 38 K in the metallic state, i.e. a continuous second order transition to a noncentrosymmetric structure (space group: P1) associated by appearance of a nominal unique polar axis along the c-axis. The phase transition is coincident with a magnetic transition at the same temperature which corresponds to a long-range antiferromagnetic order. The magnetic structure analysis and theoretical calculations prove that the antiferromagnetic ordering is the driven force for the structural transition in Pb2CoOsO6 and it represents the first double-perovskite ``ferroelectric metal'' involving a magnetic ordering. United Kingdom Engineering and Physical Sciences Research Council (EPSRC).

  16. Separability Between Valence and Conduction Bands in Transition Metal Clusters

    SciTech Connect

    Apra, Edoardo; Carter, Emily A.; Fortunelli, Alessandro

    2004-07-30

    Simplified theories of transition metal electronic structure have been postulated for many decades. Here we test one such approximation, namely separate treatments of d (valence) and s/p (conduction) electrons in transition metal clusters, within a density functional formalism. Two different basic approaches are considered: (a) an independent-band approximation, in which the d- and s/p-bands interact only via the ?-dependent components of the Kohn-Sham operator; and (b) a more realistic approximation, in which the lowest-energy d- and s/p-orbitals (separately derived) are allowed to interact through explicit off-diagonal coupling matrix elements. Results are presented for the energy differences among three structural forms (icosahedral, cuboctahedral and truncated decahedral) of 13-atom Ni and Pt clusters. We demonstrate that an explicit decoupling of the d- and s/p-bands does not produce accurate results for the clusters considered here, not even for nickel, i.e., the transition metal for which d-s/p mixing should be at its minimum. By contrast, allowing the lowest energy orbitals of the two separate bands to interact improves the results considerably, and assures a fair description of metal-metal bonding. This suggests simplified models that exclude explicit d-s/p coupling should be employed with caution.

  17. Preparation of nanoporous metal foam from high nitrogen transition metal complexes

    DOEpatents

    Tappan, Bryce C.; Huynh, My Hang V.; Hiskey, Michael A.; Son, Steven F.; Oschwald, David M.; Chavez, David E.; Naud, Darren L.

    2006-11-28

    Nanoporous metal foams are prepared by ignition of high nitrogen transition metal complexes. The ammonium salts of iron(III) tris[bi(tetrazolato)-amine], cobalt(III) tris(bi(tetrazolato)amine), and high nitrogen compounds of copper and silver were prepared as loose powders, pressed into pellets and wafers, and ignited under an inert atmosphere to form nanoporous metal foam monoliths having very high surface area and very low density.

  18. Mechanical failure and glass transition in metallic glasses

    SciTech Connect

    Egami, Takeshi

    2011-01-01

    The current majority view on the phenomenon of mechanical failure in metallic glasses appears to be that it is caused by the activity of some structural defects, such as free-volumes or shear transformation zones, and the concentration of such defects is small, only of the order of 1%. However, the recent results compel us to revise this view. Through molecular dynamics simulation it has been shown that mechanical failure is the stress-induced glass transition. According to our theory the concentration of the liquid-like sites (defects) is well over 20% at the glass transition. We suggest that the defect concentration in metallic glasses is actually very high, and percolation of such defects causes atomic avalanche and mechanical failure. In this article we discuss the glass transition, mechanical failure and viscosity from such a point of view.

  19. Spin-density functional theories and their +U and +J extensions: A comparative study of transition metals and transition metal oxides

    NASA Astrophysics Data System (ADS)

    Chen, Hanghui; Millis, Andrew J.

    2016-01-01

    Previous work on the physical content of exchange-correlation functionals that depend on both charge and spin densities is extended to elemental transition metals and a wider range of perovskite transition metal oxides. A comparison of spectra and magnetic moments calculated using charge-only and spin-dependent exchange-correlation functionals as well as their +U and +J extensions confirms previous conclusions that the spin-dependent part of the exchange-correlation functional provides an effective Hund's interaction acting on the transition metal d orbitals. For the local spin density approximation and spin-dependent generalized gradient approximation in the Perdew-Burke-Ernzerhof parametrization, the effective Hund's exchange implied by the spin dependence of the exchange correlation functional is found to be larger than 1 eV. The results indicate that at least as far as applications to transition metals and their oxides are concerned, +U , +J , and +dynamical-mean-field-theory extensions of density functional theory should be based on charge-only exchange-correlation functionals.

  20. Metal-insulator transition in films of doped semiconductor nanocrystals.

    PubMed

    Chen, Ting; Reich, K V; Kramer, Nicolaas J; Fu, Han; Kortshagen, Uwe R; Shklovskii, B I

    2016-03-01

    To fully deploy the potential of semiconductor nanocrystal films as low-cost electronic materials, a better understanding of the amount of dopants required to make their conductivity metallic is needed. In bulk semiconductors, the critical concentration of electrons at the metal-insulator transition is described by the Mott criterion. Here, we theoretically derive the critical concentration nc for films of heavily doped nanocrystals devoid of ligands at their surface and in direct contact with each other. In the accompanying experiments, we investigate the conduction mechanism in films of phosphorus-doped, ligand-free silicon nanocrystals. At the largest electron concentration achieved in our samples, which is half the predicted nc, we find that the localization length of hopping electrons is close to three times the nanocrystals diameter, indicating that the film approaches the metal-insulator transition. PMID:26618885

  1. Metal-insulator transition in films of doped semiconductor nanocrystals

    NASA Astrophysics Data System (ADS)

    Chen, Ting; Reich, K. V.; Kramer, Nicolaas J.; Fu, Han; Kortshagen, Uwe R.; Shklovskii, B. I.

    2016-03-01

    To fully deploy the potential of semiconductor nanocrystal films as low-cost electronic materials, a better understanding of the amount of dopants required to make their conductivity metallic is needed. In bulk semiconductors, the critical concentration of electrons at the metal-insulator transition is described by the Mott criterion. Here, we theoretically derive the critical concentration nc for films of heavily doped nanocrystals devoid of ligands at their surface and in direct contact with each other. In the accompanying experiments, we investigate the conduction mechanism in films of phosphorus-doped, ligand-free silicon nanocrystals. At the largest electron concentration achieved in our samples, which is half the predicted nc, we find that the localization length of hopping electrons is close to three times the nanocrystals diameter, indicating that the film approaches the metal-insulator transition.

  2. Computational Study of Metal Contacts to Monolayer Transition-Metal Dichalcogenide Semiconductors

    NASA Astrophysics Data System (ADS)

    Kang, Jiahao; Liu, Wei; Sarkar, Deblina; Jena, Debdeep; Banerjee, Kaustav

    2014-07-01

    Among various 2D materials, monolayer transition-metal dichalcogenide (mTMD) semiconductors with intrinsic band gaps (1-2 eV) are considered promising candidates for channel materials in next-generation transistors. Low-resistance metal contacts to mTMDs are crucial because currently they limit mTMD device performances. Hence, a comprehensive understanding of the atomistic nature of metal contacts to these 2D crystals is a fundamental challenge, which is not adequately addressed at present. In this paper, we report a systematic study of metal-mTMD contacts with different geometries (top contacts and edge contacts) by ab initio density-functional theory calculations, integrated with Mulliken population analysis and a semiempirical van der Waals dispersion potential model (which is critical for 2D materials and not well treated before). Particularly, In, Ti, Au, and Pd, contacts to monolayer MoS2 and WSe2 as well as Mo-MoS2 and W-WSe2 contacts are evaluated and categorized, based on their tunnel barriers, Schottky barriers, and orbital overlaps. Moreover, going beyond Schottky theory, new physics in such contact interfaces is revealed, such as the metallization of mTMDs and abnormal Fermi level pinning. Among the top contacts to MoS2, Ti and Mo show great potential to form favorable top contacts, which are both n-type contacts, while for top contacts to WSe2, W or Pd exhibits the most advantages as an n- or p-type contact, respectively. Moreover, we find that edge contacts can be highly advantageous compared to top contacts in terms of electron injection efficiency. Our formalism and the results provide guidelines that would be invaluable for designing novel 2D semiconductor devices.

  3. High throughput methods for analyzing transition metals in proteins on a microgram scale.

    PubMed

    Atanassova, Anelia; Högbom, Martin; Zamble, Deborah B

    2008-01-01

    Transition metals are among the most common ligands that contribute to the biochemical and physiological properties of proteins. In the course of structural proteomic projects, the detection of transition metal cofactors prior to the determination of a high-resolution structure is extremely beneficial. This information can be used to select tractable targets from the proteomic pipeline because the presence of a metal often improves protein stability and can be used to help solve the phasing problem in x-ray crystallography. Recombinant proteins are often purified with substoichiometric amounts of metal loaded, so additional metal may be needed to obtain the homogeneous protein solution crucial for structural analysis. Furthermore, identifying a metal cofactor provides a clue about the nature of the biological role of an unclassified protein and can be applied with structural data in the assignation of a putative function. Many of the existing methods for transition metal analysis of purified proteins have limitations, which include a requirement for a large quantity of protein or a reliance on equipment with a prohibitive cost.The authors have developed two simple high throughput methods for identifying metalloproteins on a microgram scale. Each of the techniques has distinct advantages and can be applied to address divergent experimental goals. The first method, based on simple luminescence and colorimetric reactions, is fast, cheap, and semiquantitative. The second method, which employs HPLC separation, is accurate and affords unambiguous metal identification. PMID:18542873

  4. The transition to the metallic state in low density hydrogen

    SciTech Connect

    McMinis, Jeremy; Morales, Miguel A.; Ceperley, David M.; Kim, Jeongnim

    2015-11-21

    Solid atomic hydrogen is one of the simplest systems to undergo a metal-insulator transition. Near the transition, the electronic degrees of freedom become strongly correlated and their description provides a difficult challenge for theoretical methods. As a result, the order and density of the phase transition are still subject to debate. In this work, we use diffusion quantum Monte Carlo to benchmark the transition between paramagnetic and anti-ferromagnetic body centered cubic atomic hydrogen in its ground state. We locate the density of the transition by computing the equation of state for these two phases and identify the phase transition order by computing the band gap near the phase transition. These benchmark results show that the phase transition is continuous and occurs at a Wigner-Seitz radius of r{sub s} = 2.27(3) a{sub 0}. We compare our results to previously reported density functional theory, Hedin’s GW approximation, and dynamical mean field theory results.

  5. The transition to the metallic state in low density hydrogen

    SciTech Connect

    McMinis, Jeremy; Morales, Miguel A.; Ceperley, David M.; Kim, Jeongnim

    2015-11-18

    Solid atomic hydrogen is one of the simplest systems to undergo a metal-insulator transition. Near the transition, the electronic degrees of freedom become strongly correlated and their description provides a difficult challenge for theoretical methods. As a result, the order and density of the phase transition are still subject to debate. In this work we use diffusion quantum Monte Carlo to benchmark the transition between the paramagnetic and anti-ferromagnetic phases of ground state body centered cubic atomic hydrogen. We locate the density of the transition by computing the equation of state for these two phases and identify the phase transition order by computing the band gap near the phase transition. These benchmark results show that the phase transition is continuous and occurs at a Wigner-Seitz radius of rs = 2.27(3)a0. As a result, we compare our results to previously reported density functional theory, Hedin s GW approximation, and dynamical mean field theory results.

  6. Electrocatalytic reduction of carbon dioxide on post-transition metal and metal oxide nanoparticles

    NASA Astrophysics Data System (ADS)

    White, James L.

    The electroreduction of carbon dioxide to liquid products is an important component in the utilization of CO2 and in the high-density storage of intermittent renewable energy in the form of chemical bonds. Materials based on indium and tin, which yield predominantly formic acid, have been investigated in order to gain a greater understanding of the electrochemically active species and the mechanism of CO2 reduction on these heavy post-transition metals, since prior studies on the bulk metals did not provide thermodynamically sensible reaction pathways. Nanoparticles of the oxides and hydroxides of tin and indium have been prepared and characterized by transmission electron microscopy, X-ray diffractometry, X-ray photoelectron spectroscopy, and various electrochemical methods in order to obtain structural information and analyze the role of various surface species on the CO2 reduction pathway. On both indium and tin, metastable surface-bound hydroxides bound CO2 and formed metal carbonates, which can then be reduced electrochemically. The relevant oxidation state of tin was suggested to be SnII rather than SnIV, necessitating a pre reduction to generate the CO2-binding species. Metallic indium nanoparticles partially oxidized in air and became highly efficient CO2 reduction electrocatalysts. Unit Faradaic efficiencies for formate, much higher than on bulk indium, were achieved with only 300 mV of overpotential on these particles, which possessed an oxyhydroxide shell surrounding a conductive metallic core. Alloys and mixed-metal oxide and hydroxide particles of tin and indium have also been studied for their carbon dioxide electrocatalytic capabilities, especially in comparison to the pure metal species. Additionally, a solar-driven indium-based CO2 electrolyzer was developed to investigate the overall efficiency for intermittent energy storage. The three flow cells were powered by a commercial photovoltaic array and had a maximum conversion efficiency of incident

  7. Formation of carbyne and graphyne on transition metal surfaces

    NASA Astrophysics Data System (ADS)

    Yuan, Qinghong; Ding, Feng

    2014-10-01

    The electronic and geometric structures of carbyne on various transition metal surfaces were investigated by theoretical calculations. It was found that carbyne on non-active metal surfaces has a polyynic structure, while a polycumulenic structure is more stable on active catalyst surfaces. The self-assembly of carbyne on a metal substrate could lead to the synthesis of graphyne.The electronic and geometric structures of carbyne on various transition metal surfaces were investigated by theoretical calculations. It was found that carbyne on non-active metal surfaces has a polyynic structure, while a polycumulenic structure is more stable on active catalyst surfaces. The self-assembly of carbyne on a metal substrate could lead to the synthesis of graphyne. Electronic supplementary information (ESI) available: Computational details and structural information of carbon chains on Ni(111) and Rh(111) surfaces, carbon island on Cu(111), Ni(111), Rh(111) and Ru(0001) surfaces. See DOI: 10.1039/c4nr03757j

  8. Transition Metal d-Orbital Splitting Diagrams: An Updated Educational Resource for Square Planar Transition Metal Complexes

    ERIC Educational Resources Information Center

    Bo¨rgel, Jonas; Campbell, Michael G.; Ritter, Tobias

    2016-01-01

    The presentation of d-orbital splitting diagrams for square planar transition metal complexes in textbooks and educational materials is often inconsistent and therefore confusing for students. Here we provide a concise summary of the key features of orbital splitting diagrams for square planar complexes, which we propose may be used as an updated…

  9. Steam Reforming on Transition-metal Carbides from Density-functional Theory

    SciTech Connect

    Vojvodic, Aleksandra

    2012-05-11

    A screening study of the steam reforming reaction on clean and oxygen covered early transition-metal carbides surfaces is performed by means of density-functional theory calculations. It is found that carbides provide a wide spectrum of reactivities, from too reactive via suitable to too inert. Several molybdenum-based systems are identified as possible steam reforming catalysts. The findings suggest that carbides provide a playground for reactivity tuning, comparable to the one for pure metals.

  10. Metallic-like to nonmetallic transitions in a variety of heavily oxygen deficient ferroelectrics

    SciTech Connect

    Bock, Jonathan A.; Trolier-McKinstry, Susan; Randall, Clive A.; Lee, Soonil

    2015-08-31

    The coupling between ferroelectric distortions and electron transport is an important factor in understanding ferroelectric/noncentrosymmetric materials with metallic conductivities and ferroelectric-based thermoelectrics. Here, multiple d{sup 0} ferroelectrics with a variety of crystal structures are doped via oxygen deficiency, resulting in metallic-like conduction in the paraelectric state. It is found that most of the studied systems show a metallic-like to nonmetallic transition near the paraelectric-ferroelectric transition. The metallic-like to nonmetallic transition temperature can be shifted using mechanisms that shift the paraelectric-ferroelectric transition temperature. It was found that the metallic-like to nonmetallic transition temperature could be shifted from 373 K to 273 K by varying (Ba{sub 1−x}Sr{sub x})TiO{sub 3−δ} from x = 0 to x = 0.3 and x = 1. The most probable mechanism for ferroelectric-electron transport coupling was determined to be Anderson localization associated with polarization with short-range order.

  11. Buckley Prize Talk: The Suprerconductor-(Metal)-Insulator Transition

    NASA Astrophysics Data System (ADS)

    Kapitulnik, Aharon

    2015-03-01

    While the classical theory of phase transitions has been extraordinarily successful, there are several reasons to exercise caution when applying this approach to the zero temperature superconducting transition. First, experimental identification of the relevant phases requires extrapolation to zero temperature, which becomes complicated, especially when one needs to identify sources of dissipation. In addition, since superconductivity may be highly inhomogeneous as appreciable superconducting order parameter may be concentrated in ``superconducting puddles'' due to disorder and/or spontaneous phase separation, the nature of the quantum phase transition to a superconducting state may be highly anomalous, where the system attempts to optimizes the formation of puddles with the Josephson coupling among them to obtain global superconductivity. In this talk we will review some of the consequences of these considerations, emphasizing the possible emergence of anomalous metallic phases close to the superconductor-insulator transition.

  12. Synthesis of organosiloxy: Transition metal polymers

    NASA Technical Reports Server (NTRS)

    Marano, G. A.

    1974-01-01

    The new compound, Mo(OSiPH3)4 (where Ph is C6H5) was synthesized. An overall chemical reaction which accounts for the observed products is given by the redox approach. Results indicate that Mo(OSiPH3)4 is thermally stable up to 230 C and relatively unreactive toward most common acids and bases even at elevated temperatures. Its behavior is not unlike that of Ti(OSiPH3)4.

  13. Dislocations and Plasticity in bcc Transition Metals at High Pressure

    SciTech Connect

    Yang, L H; Tang, M; Moriarty, J A

    2009-01-23

    Using first-principles electronic structure calculations, quantum-based atomistic simulations and atomistically informed dislocation dynamics (DD) simulations, we have studied individual dislocation behavior and the multiscale modeling of single-crystal plasticity in the prototype bcc transition metals Ta, Mo and V under both ambient and high pressure conditions. The primary focus in this work is on the pressure-dependent structure, mobility and interaction of a/2<111> screw dislocations, which dominate the plastic deformation properties of these materials. At the electronic scale, first-principles calculations of elasticity, ideal strength and generalized stacking fault energy surfaces have been used to validate quantum-based multi-ion interatomic potentials. At the atomistic scale, these potentials have been used in flexible Green's function boundary condition simulations to study the core structure, Peierls stress {tau}{sub P}, thermally activated kink-pair formation and mobility below {tau}{sub P}, and phonon-drag mobility above {tau}{sub P}. These results have then been distilled into analytic velocity laws and used directly in predictive microscale DD simulations of flow stress and resolved yield stress over wide ranges of pressure, temperature and strain rate.

  14. Exciton radiative lifetimes in two-dimensional transition metal dichalcogenides.

    PubMed

    Palummo, Maurizia; Bernardi, Marco; Grossman, Jeffrey C

    2015-05-13

    Light emission in two-dimensional (2D) transition metal dichalcogenides (TMDs) changes significantly with the number of layers and stacking sequence. While the electronic structure and optical absorption are well understood in 2D-TMDs, much less is known about exciton dynamics and radiative recombination. Here, we show first-principles calculations of intrinsic exciton radiative lifetimes at low temperature (4 K) and room temperature (300 K) in TMD monolayers with the chemical formula MX2 (X = Mo, W, and X = S, Se), as well as in bilayer and bulk MoS2 and in two MX2 heterobilayers. Our results elucidate the time scale and microscopic origin of light emission in TMDs. We find radiative lifetimes of a few picoseconds at low temperature and a few nanoseconds at room temperature in the monolayers and slower radiative recombination in bulk and bilayer than in monolayer MoS2. The MoS2/WS2 and MoSe2/WSe2 heterobilayers exhibit very long-lived (∼20-30 ns at room temperature) interlayer excitons constituted by electrons localized on the Mo-based and holes on the W-based monolayer. The wide radiative lifetime tunability, together with the ability shown here to predict radiative lifetimes from computations, hold unique potential to manipulate excitons in TMDs and their heterostructures for application in optoelectronics and solar energy conversion. PMID:25798735

  15. Synthesis, spectroscopic studies, antimicrobial activities and antitumor of a new monodentate V-shaped Schiff base and its transition metal complexes.

    PubMed

    Ramadan, Ramadan M; Abu Al-Nasr, Ahmad K; Noureldeen, Amani F H

    2014-11-11

    Reaction of 4-aminoacetophenone and 4-bromobenzaldehyde in ethanol resulted in the formation of the monodentate V-shaped Schiff base (E)-1-(4-((4-bromo-benzylidene)amino)phenyl)ethanone (L). Interaction of L with different di- and trivalent metal ions revealed disubstituted derivatives. The ligand and its complexes were characterized by elemental analysis, mass, IR and NMR spectrometry. Biological activities of the ligand and complexes against the Escherchia coli and Staphylococcus aureus bacterias, and the two fungus Aspergillus flavus and Candida albicans were screened. The cytotoxicity of the compounds were checked as antitumor agents on liver carcinoma cell line (HepG2). They exhibited in vitro broad range of antitumor activities towards the cell line; the [ZnL2(H2O)2](NO3)2 complex was stronger antitumor towards HepG2 cell line as well as two breast cancer cell lines (MCF7 and T47D) relative to cis-platin. PMID:24887503

  16. Comparison of Structural Relaxation Behavior in As-Cast and Pre-Annealed Zr-Based Bulk Metallic Glasses Just below Glass Transition

    DOE PAGESBeta

    Haruyama, Osami; Yoshikawa, Kazuyoshi; Yamazaki, Yoshikatsu; Yokoyama, Yoshihiko; Egami, Takeshi

    2015-04-25

    In this paper, the α-relaxation of pre-annealed Zr55Cu30Ni5Al10 bulk metallic glasses (BMGs) was compared with that of as-cast Zr-based BMGs including Zr55Cu30Ni5Al10. The α-relaxation was investigated by volume relaxation. The relaxation behavior was well described by a stretched exponential relaxation function, Φ (t) ≈ exp [ - (t/τ α )β α ], with the isothermal relaxation time, τα, and the Kohlrausch exponent, βα. The βα exhibited the strong temperature dependence for the pre-annealed BMG, while the weak temperature dependence was visualized for the as-cast BMG similar to the dynamic relaxation. The τα’s were modified by Moynihan and Narayanaswamy-Tool-Moynihan methods thatmore » reduce the difference in the thermal history of sample. Finally, as a result, the relaxation kinetics in the glass resembled that of a liquid deduced from the behavior of viscosity in the supercooled liquid.« less

  17. Comparison of Structural Relaxation Behavior in As-Cast and Pre-Annealed Zr-Based Bulk Metallic Glasses Just below Glass Transition

    SciTech Connect

    Haruyama, Osami; Yoshikawa, Kazuyoshi; Yamazaki, Yoshikatsu; Yokoyama, Yoshihiko; Egami, Takeshi

    2015-04-25

    In this paper, the α-relaxation of pre-annealed Zr55Cu30Ni5Al10 bulk metallic glasses (BMGs) was compared with that of as-cast Zr-based BMGs including Zr55Cu30Ni5Al10. The α-relaxation was investigated by volume relaxation. The relaxation behavior was well described by a stretched exponential relaxation function, Φ (t) ≈ exp [ - (t/τ α )β α ], with the isothermal relaxation time, τα, and the Kohlrausch exponent, βα. The βα exhibited the strong temperature dependence for the pre-annealed BMG, while the weak temperature dependence was visualized for the as-cast BMG similar to the dynamic relaxation. The τα’s were modified by Moynihan and Narayanaswamy-Tool-Moynihan methods that reduce the difference in the thermal history of sample. Finally, as a result, the relaxation kinetics in the glass resembled that of a liquid deduced from the behavior of viscosity in the supercooled liquid.

  18. Main Group Lewis Acid-Mediated Transformations of Transition-Metal Hydride Complexes.

    PubMed

    Maity, Ayan; Teets, Thomas S

    2016-08-10

    This Review highlights stoichiometric reactions and elementary steps of catalytic reactions involving cooperative participation of transition-metal hydrides and main group Lewis acids. Included are reactions where the transition-metal hydride acts as a reactant as well as transformations that form the metal hydride as a product. This Review is divided by reaction type, illustrating the diverse roles that Lewis acids can play in mediating transformations involving transition-metal hydrides as either reactants or products. We begin with a discussion of reactions where metal hydrides form direct adducts with Lewis acids, elaborating the structure and dynamics of the products of these reactions. The bulk of this Review focuses on reactions where the transition metal and Lewis acid act in cooperation, and includes sections on carbonyl reduction, H2 activation, and hydride elimination reactions, all of which can be promoted by Lewis acids. Also included is a section on Lewis acid-base secondary coordination sphere interactions, which can influence the reactivity of hydrides. Work from the past 50 years is included, but the majority of this Review focuses on research from the past decade, with the intent of showcasing the rapid emergence of this field and the potential for further development into the future. PMID:27164024

  19. Pseudopotentials for quantum Monte Carlo studies of transition metal oxides

    NASA Astrophysics Data System (ADS)

    Krogel, Jaron T.; Santana, Juan A.; Reboredo, Fernando A.

    2016-02-01

    Quantum Monte Carlo (QMC) calculations of transition metal oxides are partially limited by the availability of high-quality pseudopotentials that are both accurate in QMC and compatible with major plane-wave electronic structure codes. We have generated a set of neon-core pseudopotentials with small cutoff radii for the early transition metal elements Sc to Zn within the local density approximation of density functional theory. The pseudopotentials have been directly tested for accuracy within QMC by calculating the first through fourth ionization potentials of the isolated transition metal (M) atoms and the binding curve of each M-O dimer. We find the ionization potentials to be accurate to 0.16(1) eV, on average, relative to experiment. The equilibrium bond lengths of the dimers are within 0.5(1)% of experimental values, on average, and the binding energies are also typically accurate to 0.18(3) eV. The level of accuracy we find for atoms and dimers is comparable to what has recently been observed for bulk metals and oxides using the same pseudopotentials. Our QMC pseudopotential results also compare well with the findings of previous QMC studies and benchmark quantum chemical calculations.

  20. Pseudopotentials for quantum Monte Carlo studies of transition metal oxides

    DOE PAGESBeta

    Krogel, Jaron T.; Santana Palacio, Juan A.; Reboredo, Fernando A.

    2016-02-22

    Quantum Monte Carlo (QMC) calculations of transition metal oxides are partially limited by the availability of high-quality pseudopotentials that are both accurate in QMC and compatible with major plane-wave electronic structure codes. We have generated a set of neon-core pseudopotentials with small cutoff radii for the early transition metal elements Sc to Zn within the local density approximation of density functional theory. The pseudopotentials have been directly tested for accuracy within QMC by calculating the first through fourth ionization potentials of the isolated transition metal (M) atoms and the binding curve of each M-O dimer. We find the ionization potentialsmore » to be accurate to 0.16(1) eV, on average, relative to experiment. The equilibrium bond lengths of the dimers are within 0.5(1)% of experimental values, on average, and the binding energies are also typically accurate to 0.18(3) eV. The level of accuracy we find for atoms and dimers is comparable to what has recently been observed for bulk metals and oxides using the same pseudopotentials. Our QMC pseudopotential results compare well with the findings of previous QMC studies and benchmark quantum chemical calculations.« less

  1. Structure stabilities and transitions in polyhedral metal nanocrystals: An atomic-bond-relaxation approach

    NASA Astrophysics Data System (ADS)

    Zhang, Ai; Zhu, Ziming; He, Yan; Ouyang, Gang

    2012-04-01

    We present an atomic-bond-relaxation (ABR) method to illustrate a deeper insight on structure stabilities and transitions of metal nanocrystals with polyhedral structure based on the thermodynamic consideration. It has been found that the end effects in polyhedral nanocrystals induced by the atoms located at edges, side facets, and vertexes play the dominant roles for their structure performances. The theoretical predictions are well consistent with the experimental measurements and simulations, which suggest the ABR model can be an effective method to understand solid-solid phase transition of polyhedral metal nanocrystals.

  2. Molecular orbital analysis of dicarbido-transition-metal cluster compounds

    SciTech Connect

    Halet, J.; Mingos, D.M.P.

    1988-01-01

    Molecular orbital calculations on dicarbido-transition-metal carbonyl cluster compounds have shown that the bonding between C/sub 2/ and the metal cage results primarily from electron donation from the C/sub 2/ sigma/sub rho/- and ..pi..-bonding molecular orbitals and back donation from filled metallic molecular orbitals to the C/sub 2/ ..pi..* orbitals. The bonding therefore follows closely the Chatt-Dewar-Ducanson model that has been established previously for ethyne and ethene complexes but not for interstitial moieties. The C-C separation in the dicarbido clusters depends critically on the geometric constraints imposed by the metal cage and the extent of forward and back donation. In these clusters where the carbon atoms are in adjacent trigonal-prismatic sites the calculated formal bond order is between 1.0 and 1.5, which agrees well with the observed C-C bond lengths.

  3. Prebiotic coordination chemistry: The potential role of transition-metal complexes in the chemical evolution

    NASA Technical Reports Server (NTRS)

    Beck, M.

    1979-01-01

    In approaching the extremely involved and complex problem of the origin of life, consideration of the coordination chemistry appeared not only as a possibility but as a necessity. The first model experiments appear to be promising because of prebiotic-type synthesis by means of transition-metal complexes. It is especially significant that in some instances various types of vitally important substances (nucleic bases, amino acids) are formed simultaneously. There is ground to hope that systematic studies in this field will clarify the role of transition-metal complexes in the organizatorial phase of chemical evolution. It is obvious that researchers working in the fields of the chemistry of cyano and carbonyl complexes, and of the catalytic effect of transition-metal complexes are best suited to study these aspects of the attractive and interesting problem of the origin of life.

  4. Anelastic and thermal properties of ethylene/acrylic acid copolymers partially ionized with transition metals

    SciTech Connect

    Hoffman, D.M.; Matthews, F.M.; Riley, M.O.; Walkup, C.M.

    1988-01-01

    Ionomers of five 3d series transition metals (Mn, Fe, Co, Ni, and Cu), two Lanthanide series transition metals (Ce, Sm) and the IV and V series metals (Pb, Bi) were prepared by reaction with 25% solids dispersion of poly (ethylene-co-acrylic acid), EAA, in aqueous ammonia. The unreacted copolymer showed two mechanical relaxations, the glass transition at about 5C and a low temperature secondary relaxation at about -140C with 230 +- 10 kJ/mol and 50+-8 kJ/mol apparent activation energies, respectively. Typically three weight percent of the metal nitrate or acetate was reacted with the copolymer dispersion. After precipitation, drying and molding, the ionomers showed three mechanical relaxations. The low temperature ..gamma..-relaxation was quite strong and shifted about 5C higher compared to the EAA copolymer. The ..beta..-relaxation was extremely weak occurring at -62+-5C in the loss tangent at 1.0 Hz. The ..cap alpha..-relaxation or glass transition for 3% transition metal ionomers occurred at about 26+-3C for +3 oxidation states and Cu/sup +2/, but significantly higher for other +2 oxidation states (48 +- 2C for Co, Ni and 35C for Mn) based on G'' maxima at 1.0 Hz and the apparent activation energy was 220+-30kJ/mol. The two group IV and V metal ionomers were much higher loadings and had a much broader and stronger (..beta..') relaxation occurring at -6 +- 4C with 130+-10 kJ/mol activation energies. The lead ionomers were clear but the bismuth ionomer showed macroscopic phase separation. The 3d transition metal ionomers were clear and nicely colored characteristic of their ionization state except for iron which was somewhat cloudy. The Lanthanide ionomers were clear (Ce) or pale yellow (Sm) and also reasonably transparent. (16 refs., 12 figs., 5 tabs.)

  5. Valley plasmonics in transition metal dichalcogenides

    NASA Astrophysics Data System (ADS)

    Groenewald, R. E.; Rösner, M.; Schönhoff, G.; Haas, S.; Wehling, T. O.

    2016-05-01

    The rich phenomenology of plasmonic excitations in the dichalcogenides is analyzed as a function of doping. The many-body polarization, the dielectric response function, and electron energy loss spectra are calculated using an ab initio based model involving material-realistic Coulomb interactions, band structure, and spin-orbit coupling. Focusing on the representative case of MoS2, a plethora of plasmon bands are observed, originating from scattering processes within and between the conduction or valence band valleys. We discuss the resulting square-root and linear collective modes, arising from long-range versus short-range screening of the Coulomb potential. We show that the multiorbital nature of the bands and spin-orbit coupling strongly affects intervalley scattering processes by gapping certain two-particle modes at large momentum transfer.

  6. The transition to the metallic state in low density hydrogen

    DOE PAGESBeta

    McMinis, Jeremy; Morales, Miguel A.; Ceperley, David M.; Kim, Jeongnim

    2015-11-18

    Solid atomic hydrogen is one of the simplest systems to undergo a metal-insulator transition. Near the transition, the electronic degrees of freedom become strongly correlated and their description provides a difficult challenge for theoretical methods. As a result, the order and density of the phase transition are still subject to debate. In this work we use diffusion quantum Monte Carlo to benchmark the transition between the paramagnetic and anti-ferromagnetic phases of ground state body centered cubic atomic hydrogen. We locate the density of the transition by computing the equation of state for these two phases and identify the phase transitionmore » order by computing the band gap near the phase transition. These benchmark results show that the phase transition is continuous and occurs at a Wigner-Seitz radius of rs = 2.27(3)a0. As a result, we compare our results to previously reported density functional theory, Hedin s GW approximation, and dynamical mean field theory results.« less

  7. Correlated structural and electronic phase transformations in transition metal chalcogenide under high pressure

    NASA Astrophysics Data System (ADS)

    Li, Chunyu; Ke, Feng; Hu, Qingyang; Yu, Zhenhai; Zhao, Jinggeng; Chen, Zhiqiang; Yan, Hao

    2016-04-01

    Here, we report comprehensive studies on the high-pressure structural and electrical transport properties of the layered transition metal chalcogenide (Cr2S3) up to 36.3 GPa. A structural phase transition was observed in the rhombohedral Cr2S3 near 16.5 GPa by the synchrotron angle dispersive X-ray diffraction measurement using a diamond anvil cell. Through in situ resistance measurement, the electric resistance value was detected to decrease by an order of three over the pressure range of 7-15 GPa coincided with the structural phase transition. Measurements on the temperature dependence of resistivity indicate that it is a semiconductor-to-metal transition in nature. The results were also confirmed by the electronic energy band calculations. Above results may shed a light on optimizing the performance of Cr2S3 based applications under extreme conditions.

  8. Structure, bonding, and catalytic activity of monodisperse, transition-metal-substituted CeO2 nanoparticles.

    PubMed

    Elias, Joseph S; Risch, Marcel; Giordano, Livia; Mansour, Azzam N; Shao-Horn, Yang

    2014-12-10

    We present a simple and generalizable synthetic route toward phase-pure, monodisperse transition-metal-substituted ceria nanoparticles (M0.1Ce0.9O2-x, M = Mn, Fe, Co, Ni, Cu). The solution-based pyrolysis of a series of heterobimetallic Schiff base complexes ensures a rigorous control of the size, morphology and composition of 3 nm M0.1Ce0.9O2-x crystallites for CO oxidation catalysis and other applications. X-ray absorption spectroscopy confirms the dispersion of aliovalent (M(3+) and M(2+)) transition metal ions into the ceria matrix without the formation of any bulk transition metal oxide phases, while steady-state CO oxidation catalysis reveals an order of magnitude increase in catalytic activity with copper substitution. Density functional calculations of model slabs of these compounds confirm the stabilization of M(3+) and M(2+) in the lattice of CeO2. These results highlight the role of the host CeO2 lattice in stabilizing high oxidation states of aliovalent transition metal dopants that ordinarily would be intractable, such as Cu(3+), as well as demonstrating a rational approach to catalyst design. The current work demonstrates, for the first time, a generalizable approach for the preparation of transition-metal-substituted CeO2 for a broad range of transition metals with unparalleled synthetic control and illustrates that Cu(3+) is implicated in the mechanism for CO oxidation on CuO-CeO2 catalysts. PMID:25406101

  9. Propentdyopent: the scaffold of a heme metabolite as an electron reservoir in transition metal complexes.

    PubMed

    Gautam, R; Chang, T M; Astashkin, A V; Lincoln, K M; Tomat, E

    2016-05-01

    The dipyrrin-1,9-dione scaffold of heme metabolite propendyopent coordinates late transition metals (Co, Ni, Cu, and Zn) forming homoleptic, pseudo-tetrahedral complexes. Electrochemical and spectroscopic studies reveal that the monoanionic, bidentate ligands behave as electron reservoirs as the complexes reversibly host one or two ligand-based radicals. PMID:27109437

  10. Cross-linking proteins with bimetallic tetracarboxylate compounds of transition metals

    DOEpatents

    Kostic, N.M.; Chen, J.

    1991-03-05

    Stable cross-linked complexes of transition-metal tetracarboxylates and proteins are formed. The preferred transition-metal is rhodium. The protein may be collagen or an enzyme such as a proteolytic enzyme. No Drawings

  11. Cross-linking proteins with bimetallic tetracarboxylate compounds of transition metals

    DOEpatents

    Kostic, Nenad M.; Chen, Jian

    1991-03-05

    Stable cross-linked complexes of transition-metal tetracarboxylates and proteins are formed. The preferred transition-metal is rhodium. The protein may be collagen or an enzyme such as a proteolytic enzyme.

  12. An Alternative Approach to the Teaching of Systematic Transition Metal Chemistry.

    ERIC Educational Resources Information Center

    Hathaway, Brian

    1979-01-01

    Presents an alternative approach to teaching Systematic Transition Metal Chemistry with the transition metal chemistry skeleton features of interest. The "skeleton" is intended as a guide to predicting the chemistry of a selected compound. (Author/SA)

  13. Novel photoinduced phase transitions in transition metal oxides and diluted magnetic semiconductors

    PubMed Central

    2012-01-01

    Some transition metal oxides have frustrated electronic states under multiphase competition due to strongly correlated d electrons with spin, charge, and orbital degrees of freedom and exhibit drastic responses to external stimuli such as optical excitation. Here, we present photoemission studies on Pr0.55(Ca1 − ySry)0.45MnO3 (y = 0.25), SrTiO3, and Ti1 − xCoxO2 (x = 0.05, 0.10) under laser illumination and discuss electronic structural changes induced by optical excitation in these strongly correlated oxides. We discuss the novel photoinduced phase transitions in these transition metal oxides and diluted magnetic semiconductors on the basis of polaronic pictures such as orbital, ferromagnetic, and ferroelectric polarons. PMID:23092248

  14. Magnetic Exchange Couplings in Transition Metal Complexes from DFT

    NASA Astrophysics Data System (ADS)

    Peralta, Juan

    In this talk I will review our current efforts for the evaluation of magnetic exchange couplings in transition metal complexes from density functional theory. I will focus on the performance of different DFT approximations, including a variety of hybrid density functionals, and show that hybrid density functionals containing approximately 30% Hartree-Fock type exchange are in general among the best choice in terms of accuracy. I will also describe a novel computational method to evaluate exchange coupling parameters using analytic self-consistent linear response theory. This method avoids the explicit evaluation of energy differences, which can become impractical for large systems. Our approach is based on the evaluation of the transversal magnetic torque between two magnetic centers for a given spin configuration using explicit constraints of the local magnetization direction via Lagrange multipliers. This method is applicable in combination with any modern density functional with a noncollinear spin generalization and can be utilized as a ``black-box''. I will show proof-of-concept calculations in frustrated Fe7IIIdisk-shaped clusters, and dinuclear CuII, FeIII, and heteronuclear complexes. NSF DMR-1206920.

  15. Magnetic ground state of semiconducting transition-metal trichalcogenide monolayers

    SciTech Connect

    Sivadas, Nikhil; Daniels, Matthew W.; Swendsen, Robert H.; Okamoto, Satoshi; Xiao, Di

    2015-06-16

    Layered transition-metal trichalcogenides with the chemical formula ABX3 have attracted recent interest as potential candidates for two-dimensional magnets. Using first-principles calculations within density functional theory, we investigate the magnetic ground states of monolayers of Mn- and Cr-based semiconducting trichalcogenides.We show that the second and third nearest-neighbor exchange interactions (J2 and J3) between magnetic ions, which have been largely overlooked in previous theoretical studies, are crucial in determining the magnetic ground state. Specifically, we find that monolayer CrSiTe3 is an antiferromagnet with a zigzag spin texture due to significant contribution from J3, whereas CrGeTe3 is a ferromagnet with a Curie temperature of 106 K. Monolayers of Mn compounds (MnPS3 and MnPSe3) always show antiferromagnetic N eel order. We identify the physical origin of various exchange interactions, and demonstrate that strain can be an effective knob for tuning the magnetic properties. Possible magnetic ordering in the bulk is also discussed. In conclusion, our study suggests that ABX3 can be a promising platform to explore two-dimensional magnetic phenomena.

  16. Magnetic ground state of semiconducting transition-metal trichalcogenide monolayers

    DOE PAGESBeta

    Sivadas, Nikhil; Daniels, Matthew W.; Swendsen, Robert H.; Okamoto, Satoshi; Xiao, Di

    2015-06-16

    Layered transition-metal trichalcogenides with the chemical formula ABX3 have attracted recent interest as potential candidates for two-dimensional magnets. Using first-principles calculations within density functional theory, we investigate the magnetic ground states of monolayers of Mn- and Cr-based semiconducting trichalcogenides.We show that the second and third nearest-neighbor exchange interactions (J2 and J3) between magnetic ions, which have been largely overlooked in previous theoretical studies, are crucial in determining the magnetic ground state. Specifically, we find that monolayer CrSiTe3 is an antiferromagnet with a zigzag spin texture due to significant contribution from J3, whereas CrGeTe3 is a ferromagnet with a Curie temperaturemore » of 106 K. Monolayers of Mn compounds (MnPS3 and MnPSe3) always show antiferromagnetic N eel order. We identify the physical origin of various exchange interactions, and demonstrate that strain can be an effective knob for tuning the magnetic properties. Possible magnetic ordering in the bulk is also discussed. In conclusion, our study suggests that ABX3 can be a promising platform to explore two-dimensional magnetic phenomena.« less

  17. Spin-orbit engineering in transition metal dichalcogenide alloy monolayers.

    PubMed

    Wang, Gang; Robert, Cedric; Suslu, Aslihan; Chen, Bin; Yang, Sijie; Alamdari, Sarah; Gerber, Iann C; Amand, Thierry; Marie, Xavier; Tongay, Sefaattin; Urbaszek, Bernhard

    2015-01-01

    Binary transition metal dichalcogenide monolayers share common properties such as a direct optical bandgap, spin-orbit splittings of hundreds of meV, light-matter interaction dominated by robust excitons and coupled spin-valley states. Here we demonstrate spin-orbit-engineering in Mo(1-x)WxSe2 alloy monolayers for optoelectronics and applications based on spin- and valley-control. We probe the impact of the tuning of the conduction band spin-orbit spin-splitting on the bright versus dark exciton population. For MoSe2 monolayers, the photoluminescence intensity decreases as a function of temperature by an order of magnitude (4-300 K), whereas for WSe2 we measure surprisingly an order of magnitude increase. The ternary material shows a trend between these two extreme behaviours. We also show a non-linear increase of the valley polarization as a function of tungsten concentration, where 40% tungsten incorporation is sufficient to achieve valley polarization as high as in binary WSe2. PMID:26657930

  18. APCVD Transition Metal Oxides - Functional Layers in "Smart windows"

    NASA Astrophysics Data System (ADS)

    Gesheva, K. A.; Ivanova, T. M.; Bodurov, G. K.

    2014-11-01

    Transition metal oxides (TMO) exhibit electrochromic effect. Under a small voltage they change their optical transmittance from transparent to collored (absorbing) state. The individual material can manifest its electrochromic properties only when it is part of electrochromic (EC) multilayer system. Smart window is controlling the energy of solar flux entering the building or car and makes the interiors comfortable and energy utilization more effective. Recently the efforts of material researchers in this field are directed to price decreasing. APCVD technology is considered as promissing as this process permits flowthrough large-scale production process. The paper presents results on device optimization based on WO3-MoO3 working electrode. Extensive research reveals that WO3-MoO3 structure combines positive features of single oxides: excellent electrochromic performance of WO3 and better kinetic properties of MoO3 deposition. The achieved color efficiency of APCVD WO3-MoO3 films is 200cm2/C and optical modulation of 65-70% are practically favorable electrochromic characteristics. To respond to low cost requirement, the expensive hexacarbonyl can be replaced with acetylacetonate. We have started with this precursor to fabricate mixed WxV1-xO3 films. The films possess excellent surface coverage and high growth-rate. CVD deposition of VO2, a promissing thermochromic thin film material is also presented.

  19. Superconductivity Series in Transition Metal Dichalcogenides by Ionic Gating

    PubMed Central

    Shi, Wu; Ye, Jianting; Zhang, Yijin; Suzuki, Ryuji; Yoshida, Masaro; Miyazaki, Jun; Inoue, Naoko; Saito, Yu; Iwasa, Yoshihiro

    2015-01-01

    Functionalities of two-dimensional (2D) crystals based on semiconducting transition metal dichalcogenides (TMDs) have now stemmed from simple field effect transistors (FETs) to a variety of electronic and opto-valleytronic devices, and even to superconductivity. Among them, superconductivity is the least studied property in TMDs due to methodological difficulty accessing it in different TMD species. Here, we report the systematic study of superconductivity in MoSe2, MoTe2 and WS2 by ionic gating in different regimes. Electrostatic gating using ionic liquid was able to induce superconductivity in MoSe2 but not in MoTe2 because of inefficient electron accumulation limited by electronic band alignment. Alternative gating using KClO4/polyethylene glycol enabled a crossover from surface doping to bulk doping, which induced superconductivities in MoTe2 and WS2 electrochemically. These new varieties greatly enriched the TMD superconductor families and unveiled critical methodology to expand the capability of ionic gating to other materials. PMID:26235962

  20. Spin-orbit engineering in transition metal dichalcogenide alloy monolayers

    PubMed Central

    Wang, Gang; Robert, Cedric; Suslu, Aslihan; Chen, Bin; Yang, Sijie; Alamdari, Sarah; Gerber, Iann C.; Amand, Thierry; Marie, Xavier; Tongay, Sefaattin; Urbaszek, Bernhard

    2015-01-01

    Binary transition metal dichalcogenide monolayers share common properties such as a direct optical bandgap, spin-orbit splittings of hundreds of meV, light–matter interaction dominated by robust excitons and coupled spin-valley states. Here we demonstrate spin-orbit-engineering in Mo(1−x)WxSe2 alloy monolayers for optoelectronics and applications based on spin- and valley-control. We probe the impact of the tuning of the conduction band spin-orbit spin-splitting on the bright versus dark exciton population. For MoSe2 monolayers, the photoluminescence intensity decreases as a function of temperature by an order of magnitude (4–300 K), whereas for WSe2 we measure surprisingly an order of magnitude increase. The ternary material shows a trend between these two extreme behaviours. We also show a non-linear increase of the valley polarization as a function of tungsten concentration, where 40% tungsten incorporation is sufficient to achieve valley polarization as high as in binary WSe2. PMID:26657930

  1. Magnetic brightening of dark excitons in transitional metal dichalcogenides

    NASA Astrophysics Data System (ADS)

    Zhang, Xiao-Xiao; Lu, Zhengguang; Cao, Ting; Zhang, Fan; Hone, James; Louie, Steven G.; Li, Zhiqiang; Smirnov, Dmitry; Heinz, Tony

    Transitional metal dichalcogenides (TMDC) in the MX2 (M = Mo, W, X = S, Se) family represent an excellent platform to study of excitonic effects. At monolayer thickness, these materials exhibit both direct band-gap character and enhanced excitonic interactions. Theoretical studies suggest that both the valence and conduction bands are split and exhibit spin polarized character at the K/K' valleys. The lowest energy band-edge excitons are predicted to have different spin configurations for different materials in this family. When the lowest lying exciton has parallel electron and hole spin, radiative decay is forbidden and the state is dark. Here we demonstrate that by applying an in-plane magnetic field we can perturb the exciton spin configuration and brighten this state, allowing it to undergo radiative decay. We identify such a brightened dark state by the emergence of a new emission peak lying below the absorption peak, with a strength growing with applied in-plane magnetic field. On the other hand, for monolayer MoSe2, where no low-lying dark state is expected, we do not see the growth of a new emission feature under application of an in-plane magnetic field. Our experimental findings are in agreement with the calculated properties of dark excitons based on GW plus Bethe-Salpeter equation approach

  2. Induce magnetism into silicene by embedding transition-metal atoms

    SciTech Connect

    Sun, Xiaotian; Wang, Lu E-mail: yyli@suda.edu.cn; Lin, Haiping; Hou, Tingjun; Li, Youyong E-mail: yyli@suda.edu.cn

    2015-06-01

    Embedding transition-metal (TM) atoms into nonmagnetic nanomaterials is an efficient way to induce magnetism. Using first-principles calculations, we systematically investigated the structural stability and magnetic properties of TM atoms from Sc to Zn embedded into silicene with single vacancy (SV) and double vacancies (DV). The binding energies for different TM atoms correlate with the TM d-shell electrons. Sc, Ti, and Co show the largest binding energies of as high as 6 eV, while Zn has the lowest binding energy of about 2 eV. The magnetic moment of silicene can be modulated by embedding TM atoms from V to Co, which mainly comes from the 3d orbitals of TM along with partly contributions from the neighboring Si atoms. Fe atom on SV and Mn atom on DV have the largest magnetic moment of more than 3 μB. In addition, we find that doping of N or C atoms on the vacancy site could greatly enhance the magnetism of the systems. Our results provide a promising approach to design silicene-based nanoelectronics and spintronics device.

  3. Strain engineered optoelectronic properties of transition metal dichalcogenides lateral heterostructures

    NASA Astrophysics Data System (ADS)

    Lee, Jaekwang; Yoon, Mina

    2015-03-01

    Most three-dimensional bulk-scale materials rarely survive beyond 1% strain, while recently spotlighted two-dimensional (2-D) materials can sustain a high elastic strain (up to 10%) to optimize optical quantities such as band gaps and absorption spectra governing optoelectronic device performance. Despite the enormous interest in strained 2-D materials, most researches are focused on single materials or vertical heterostructures where precise control of stacking orientation is challenging. Here, using first-principles density-functional calculations, we explore how uniaxial tensile strains modify overall electronic and optical properties of transition metal dichalcogenides lateral heterostructures, such as MoX2/WX2 (X =S, Se). Based on the detailed optoelectronic information, we predict the optimal strain condition for maximal power efficiency. Furthermore, we find that uniaxial tensile strain readily develops a continuously varying direct-bandgap across the lateral heterojunctions, which results in the broad range absorption of solar spectrum useful for future optoelectronic devices. This research was conducted at the CNMS, which is sponsored at Oak Ridge National Laboratory (ORNL) by the Office of Basic Energy Sciences, U.S. Department of Energy; a portion of theory work was supported by the LDRD Program of ORNL.

  4. RKKY interaction in transition-metal dichalcogenide nanoflakes

    NASA Astrophysics Data System (ADS)

    Avalos-Ovando, Oscar; Mastrogiuseppe, Diego; Ulloa, Sergio

    2015-03-01

    Transition metal dichalcogenides (TMDs) are layered crystals with unique electronic and optical properties, and are promising candidates for a new generation of semiconductor-based devices, mainly when exfoliated to one or a few layers. The process of exfoliation often produces nanoscale samples -flakes- with different shapes and boundaries. These flakes might have applications as quantum dots with novel characteristics. One interesting topic relates to the presence of magnetic impurities and their interaction. In combination with strong spin-orbit coupling and valley degrees of freedom, TMDs might have a great impact in the field of spintronics. Using an effective low-energy two-orbital tight-binding model, we study the Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction between two magnetic impurities in 2D TMD nanoflakes. We consider different geometries and terminations, analyzing the effect of the sample size. Our results show the behavior of the interaction for impurities sitting at different positions in the flake, and its possible tunability with the electron/hole concentration. The magnetic impurities can be intrinsic to the sample production process or can be introduced extrinsically. Our results can be tested with local probes, such as spin-polarized STM. Supported by NSF DMR MWN/CIAM.

  5. Dynamics and Control in Complex Transition Metal Oxides

    NASA Astrophysics Data System (ADS)

    Zhang, J.; Averitt, R. D.

    2014-07-01

    Advances in the synthesis, growth, and characterization of complex transition metal oxides coupled with new experimental techniques in ultrafast optical spectroscopy have ushered in an exciting era of dynamics and control in these materials. Experiments utilizing femtosecond optical pulses can initiate and probe dynamics of the spin, lattice, orbital, and charge degrees of freedom. Major goals include (a) determining how interaction and competition between the relevant degrees of freedom determine macroscopic functionality in transition metal oxides (TMOs) and (b) searching for hidden phases in TMOs by controlling dynamic trajectories in a complex and pliable energy landscape. Advances in creating intense pulses from the far-IR spectrum through the visible spectrum enable mode-selective excitation to facilitate exploration of these possibilities. This review covers recent developments in this emerging field and presents examples that include the cuprates, manganites, and vanadates.

  6. Wetting Transitions of Inert Gases on Alkali Metal Surfaces

    NASA Astrophysics Data System (ADS)

    Bojan, M. J.; McDonald, I. A.; Cole, M. W.; Steele, W. A.

    1996-03-01

    Theoretical and experimental discoveries have been made recently of wetting and prewetting transitions of helium and hydrogen films on alkali metal surfaces [1,2]. New experiments show anomalous nonwetting behavior of Ne on Rb and Cs [3]. Building on earlier work [4], we have done and will describe results from the first Monte Carlo simulations showing wetting transitions for classical gases on alkali metal surfaces. * Research supported by an NSF Materials Research Group grant. 1. R. B.Hallock, J. Low Temp. Phys. 101, 31, 1995 2. M. W. Cole, J. Low Temp. Phys. 101, 25, 1995. 3. G. B. Hess, M. Sabatini, and M. H. W. Chan, unpublished 4. J. E. Finn and P. A. Monson, Phys. Rev. A 39, 6402, 1989.

  7. Exciton complexes in low dimensional transition metal dichalcogenides

    NASA Astrophysics Data System (ADS)

    Thilagam, A.

    2014-08-01

    We examine the excitonic properties of layered configurations of low dimensional transition metal dichalcogenides (LTMDCs) using the fractional dimensional space approach. The binding energies of the exciton, trion, and biexciton in LTMDCs of varying layers are analyzed, and linked to the dimensionality parameter α, which provides insight into critical electro-optical properties (relative oscillator strength, absorption spectrum, exciton-exciton interaction) of the material systems. The usefulness of α is highlighted by its independence of the physical mechanisms underlying the confinement effects of geometrical structures. Our estimates of the binding energies of exciton complexes for the monolayer configuration of transition metal dichalcogenides suggest a non-collinear structure for the trion and a positronium-molecule-like square structure for the biexciton.

  8. Exciton complexes in low dimensional transition metal dichalcogenides

    SciTech Connect

    Thilagam, A.

    2014-08-07

    We examine the excitonic properties of layered configurations of low dimensional transition metal dichalcogenides (LTMDCs) using the fractional dimensional space approach. The binding energies of the exciton, trion, and biexciton in LTMDCs of varying layers are analyzed, and linked to the dimensionality parameter α, which provides insight into critical electro-optical properties (relative oscillator strength, absorption spectrum, exciton-exciton interaction) of the material systems. The usefulness of α is highlighted by its independence of the physical mechanisms underlying the confinement effects of geometrical structures. Our estimates of the binding energies of exciton complexes for the monolayer configuration of transition metal dichalcogenides suggest a non-collinear structure for the trion and a positronium-molecule-like square structure for the biexciton.

  9. Recent Advances in Transition Metal-Catalyzed Glycosylation

    PubMed Central

    McKay, Matthew J.; Nguyen, Hien M.

    2012-01-01

    Having access to mild and operationally simple techniques for attaining carbohydrate targets will be necessary to facilitate advancement in biological, medicinal, and pharmacological research. Even with the abundance of elegant reports for generating glycosidic linkages, stereoselective construction of α- and β-oligosaccharides and glycoconjugates is by no means trivial. In an era where expanded awareness of the impact we are having on the environment drives the state-of-the-art, synthetic chemists are tasked with developing cleaner and more efficient reactions for achieving their transformations. This movement imparts the value that prevention of waste is always superior to its treatment or cleanup. This review will highlight recent advancement in this regard by examining strategies that employ transition metal catalysis in the synthesis of oligosaccharides and glycoconjugates. These methods are mild and effective for constructing glycosidic bonds with reduced levels of waste through utilization of sub-stoichiometric amounts of transition metals to promote the glycosylation. PMID:22924154

  10. Inherited (In)stabilities in Transition Metal Superlattices

    NASA Astrophysics Data System (ADS)

    Rudin, Sven

    2011-03-01

    Many transition metals exhibit a solid phase with a body-centered cubic (bcc) crystal structure. For some elements, e.g., tungsten (W), bcc is the only solid phase; for others, e.g., titanium (Ti), the bcc phase only appears at high temperatures. Titanium's high-temperature bcc phase exhibits soft phonon modes. These reflect the atomic movements upon transformation into the low-temperature phases. One such mode shows atomic displacements that also appear in the top few layers of tungsten's surface reconstruction. Superlattices constructed from alternating nanometer-thick layers of W and Ti would allow the two displacement patterns to interact. The work presented here uses density functional theory calculations to predict how the structure and mechanical response of such superlattices depends on the choice of transition metal elements and the layer thicknesses.

  11. Transition metal catalysis in the generation of natural gas

    SciTech Connect

    Mango, F.D.

    1995-12-31

    The view that natural gas is thermolytic, coming from decomposing organic debris, has remained almost unchallenged for nearly half a century. Disturbing contradictions exist, however: Oil is found at great depth, at temperatures where only gas should exist and oil and gas deposits show no evidence of the thermolytic debris indicative of oil decomposing to gas. Moreover, laboratory attempts to duplicate the composition of natural gas, which is typically between 60 and 95+ wt% methane in C{sub 1}-C{sub 4}, have produced insufficient amounts of methane (10 to 60%). It has been suggested that natural gas may be generated catalytically, promoted by the transition metals in carbonaceous sedimentary rocks. This talk will discuss experimental results that support this hypothesis. Various transition metals, as pure compounds and in source rocks, will be shown to generate a catalytic gas that is identical to natural gas. Kinetic results suggest robust catalytic activity under moderate catagenetic conditions.

  12. Metallic ferromagnetism-insulating charge order transition in doped manganites

    NASA Astrophysics Data System (ADS)

    Phan, Van-Nham; Ninh, Quoc-Huy; Tran, Minh-Tien

    2016-04-01

    We show that an interplay of double exchange and impurity randomness can explain the competition between metal-ferromagnetic and insulating charge ordered states in doped manganites. The double exchange is simplified in the Ising type, whereas the randomness is modeled by the Falicov-Kimball binary distribution. The combined model is considered in a framework of dynamical mean-field theory. Using the Kubo-Greenwood formalism, the transport coefficients are explicitly expressed in terms of single-particle spectral functions. Dividing the system into two sublattices we have pointed out a direct calculation to the checkerboard charge order parameter and the magnetizations. Numerical results show us that the checkerboard charge order can settle inside the ferromagnetic state at low temperature. An insulator-metal transition is also found at the point of the checkerboard charge order-ferromagnetic transition.

  13. Valley-selective harmonic generations in transition metal dichalcogenide monolayers

    NASA Astrophysics Data System (ADS)

    Cheng, Jingxin; Jiang, Tao; Shan, Yuwei; Li, Yingguo; Chen, Xianhui; Shen, Y. R.; Liu, Weitao; Wu, Shiwei

    Transition metal dichalcogenide monolayer has emerged as another star in the family of atomically thin two dimensional materials. Different from graphene, the two sublattices in its honeycomb-like structure are occupied by different atoms, leading to the reduced rotational symmetry from six fold to three fold. The reduced symmetry and dimension not only result in many intriguing physics such as valley and excitons, but also lead to rich nonlinear optical phenomena such as strong second harmonic generation. In this talk, we will present a systematic study on linearly and circularly polarized harmonic generations in this wonder material. We show that both the second and third harmonic generations follow the conservation of angular momentum and are valley-selective. Furthermore, these nonlinear optical processes could be used as a powerful imaging tool for studying transition metal dichalcogenide monolayers and other similar 2D materials.

  14. A supramolecular microenvironment strategy for transition metal catalysis.

    PubMed

    Kaphan, David M; Levin, Mark D; Bergman, Robert G; Raymond, Kenneth N; Toste, F Dean

    2015-12-01

    A self-assembled supramolecular complex is reported to catalyze alkyl-alkyl reductive elimination from high-valent transition metal complexes [such as gold(III) and platinum(IV)], the central bond-forming elementary step in many catalytic processes. The catalytic microenvironment of the supramolecular assembly acts as a functional enzyme mimic, applying the concepts of enzymatic catalysis to a reactivity manifold not represented in biology. Kinetic experiments delineate a Michaelis-Menten-type mechanism, with measured rate accelerations (k(cat)/k(uncat)) up to 1.9 × 10(7) (here k(cat) and k(uncat) are the Michaelis-Menten enzymatic rate constant and observed uncatalyzed rate constant, respectively). This modality has further been incorporated into a dual catalytic cross-coupling reaction, which requires both the supramolecular microenvironment catalyst and the transition metal catalyst operating in concert to achieve efficient turnover. PMID:26785485

  15. Ductile-to-brittle transition in spallation of metallic glasses

    SciTech Connect

    Huang, X.; Ling, Z.; Dai, L. H.

    2014-10-14

    In this paper, the spallation behavior of a binary metallic glass Cu{sub 50}Zr{sub 50} is investigated with molecular dynamics simulations. With increasing the impact velocity, micro-voids induced by tensile pulses become smaller and more concentrated. The phenomenon suggests a ductile-to-brittle transition during the spallation process. Further investigation indicates that the transition is controlled by the interaction between void nucleation and growth, which can be regarded as a competition between tension transformation zones (TTZs) and shear transformation zones (STZs) at atomic scale. As impact velocities become higher, the stress amplitude and temperature rise in the spall region increase and micro-structures of the material become more unstable. Therefore, TTZs are prone to activation in metallic glasses, leading to a brittle behavior during the spallation process.

  16. Meyer Neldel rule application to silicon supersaturated with transition metals

    NASA Astrophysics Data System (ADS)

    García-Hemme, Eric; García-Hernansanz, Rodrigo; Olea, Javier; Pastor, David; del Prado, Alvaro; Mártil, Ignacio; González-Díaz, Germán

    2015-02-01

    This paper presents the results for the transverse conductance across a bilayer formed by supersaturating with diverse transition metals a thin layer of a silicon wafer. The layer is formed by ion implantation and annealed by pulsed laser melting. The transverse conductance is exponentially activated, obtaining values ranging from 0.018 to 0.7 eV for the activation energy and pre-exponential factors of 10-2-1012 S depending on the annealing energy density. A semi-logarithmic plot of the pre-exponential factor versus activation energy shows an almost perfect linear behaviour as stated by the Meyer Neldel rule. The Meyer Neldel energy obtained for implantation with different transition metals and also annealed in different conditions is 22 meV, which is within the range of silicon phonons, thus confirming the hypothesis of the multi excitation entropy theory.

  17. [Spectroscopic studies on transition metal ions in colored diamonds].

    PubMed

    Meng, Yu-Fei; Peng, Ming-Sheng

    2004-07-01

    Transition metals like nickel, cobalt and iron have been often used as solvent catalysts in high pressure high temperature (HPHT) synthesis of diamond, and nickel and cobalt ions have been found in diamond lattice. Available studies indicated that nickel and cobalt ions could enter the lattice as interstitial or substitutional impurities and form complexes with nitrogen. Polarized microscopy, SEM-EDS, EPR, PL and FTIR have been used in this study to investigate six fancy color natural and synthetic diamonds in order to determine the spectroscopic characteristics and the existing forms of transition metal ions in colored diamond lattice. Cobalt-related optical centers were first found in natural chameleon diamonds, and some new nickel and cobalt-related optical and EPR centers have also been detected in these diamond samples. PMID:15766067

  18. Mechanical properties of 4d transition metals in molten state

    NASA Astrophysics Data System (ADS)

    Singh, Deobrat; Sonvane, Yogesh; Thakor, P. B.

    2016-05-01

    Mechanical properties of 4d transition metals in molten state have been studied in the present study. We have calculated mechanical properties such as isothermal bulk modulus (B), modulus of rigidity (G), Young's modulus (Y) and Hardness have also been calculated from the elastic part of the Phonon dispersion curve (PDC). To describe the structural information, we have used different structure factor S(q) using Percus-Yevick hard sphere (PYHS) reference systems along with our newly constructed parameter free model potential.To see the influence of exchange and correlation effect on the above said properties of 3d liquid transition metals, we have used Sarkar et al (S)local field correction functions. Present results have been found good in agreement with available experimental data.

  19. Photonics and optoelectronics of 2D semiconductor transition metal dichalcogenides

    NASA Astrophysics Data System (ADS)

    Mak, Kin Fai; Shan, Jie

    2016-04-01

    Recent advances in the development of atomically thin layers of van der Waals bonded solids have opened up new possibilities for the exploration of 2D physics as well as for materials for applications. Among them, semiconductor transition metal dichalcogenides, MX2 (M = Mo, W; X = S, Se), have bandgaps in the near-infrared to the visible region, in contrast to the zero bandgap of graphene. In the monolayer limit, these materials have been shown to possess direct bandgaps, a property well suited for photonics and optoelectronics applications. Here, we review the electronic and optical properties and the recent progress in applications of 2D semiconductor transition metal dichalcogenides with emphasis on strong excitonic effects, and spin- and valley-dependent properties.

  20. Metal-insulator and charge ordering transitions in oxide nanostructures

    NASA Astrophysics Data System (ADS)

    Singh, Sujay Kumar

    Strongly correlated oxides are a class of materials wherein interplay of various degrees of freedom results in novel electronic and magnetic phenomena. Vanadium oxides are widely studied correlated materials that exhibit metal-insulator transitions (MIT) in a wide temperature range from 70 K to 380 K. In this Thesis, results from electrical transport measurements on vanadium dioxide (VO2) and vanadium oxide bronze (MxV 2O5) (where M: alkali, alkaline earth, and transition metal cations) are presented and discussed. Although the MIT in VO2 has been studied for more than 50 years, the microscopic origin of the transition is still debated since a slew of external parameters such as light, voltage, and strain are found to significantly alter the transition. Furthermore, recent works on electrically driven switching in VO2 have shown that the role of Joule heating to be a major cause as opposed to electric field. We explore the mechanisms behind the electrically driven switching in single crystalline nanobeams of VO2 through DC and AC transport measurements. The harmonic analysis of the AC measurement data shows that non-uniform Joule heating causes electronic inhomogeneities to develop within the nanobeam and is responsible for driving the transition in VO2. Surprisingly, field assisted emission mechanisms such as Poole-Frenkel effect is found to be absent and the role of percolation is also identified in the electrically driven transition. This Thesis also provides a new insight into the mechanisms behind the electrolyte gating induced resistance modulation and the suppression of MIT in VO2. We show that the metallic phase of VO2 induced by electrolyte gating is due to an electrochemical process and can be both reversible and irreversible under different conditions. The kinetics of the redox processes increase with temperature; a complete suppression of the transition and the stabilization of the metallic phase are achievable by gating in the rutile metallic phase

  1. Growth of Hollow Transition Metal (Fe, Co, Ni) Oxide Nanoparticles on Graphene Sheets through Kirkendall Effect as Anodes for High-Performance Lithium-Ion Batteries.

    PubMed

    Yu, Xianbo; Qu, Bin; Zhao, Yang; Li, Chunyan; Chen, Yujin; Sun, Chunwen; Gao, Peng; Zhu, Chunling

    2016-01-26

    A general strategy based on the nanoscale Kirkendall effect has been developed to grow hollow transition metal (Fe, Co or Ni) oxide nanoparticles on graphene sheets. When applied as lithium-ion battery anodes, these hollow transition metal oxide-based composites exhibit excellent electrochemical performance, with high reversible capacities and long-term stabilities at a high current density, superior to most transition metal oxides reported to date. PMID:26502895

  2. Effects of alloying elements on fracture toughness in the transition temperature region of base metals and simulated heat-affected zones of Mn-Mo-Ni low-alloy steels

    NASA Astrophysics Data System (ADS)

    Kim, Sangho; Im, Young-Roc; Lee, Sunghak; Lee, Hu-Chul; Kim, Sung-Joon; Hong, Jun Hwa

    2004-07-01

    This study is concerned with the effects of alloying elements on fracture toughness in the transition temperature region of base metals and heat-affected zones (HAZs) of Mn-Mo-Ni low-alloy steels. Three kinds of steels whose compositions were varied from the composition specification of SA 508 steel (grade 3) were fabricated by vacuum-induction melting and heat treatment, and their fracture toughness was examined using an ASTM E1921 standard test method. In the steels that have decreased C and increased Mo and Ni content, the number of fine M2C carbides was greatly increased and the number of coarse M3C carbides was decreased, thereby leading to the simultaneous improvement of tensile properties and fracture toughness. Brittle martensite-austenite (M-A) constituents were also formed in these steels during cooling, but did not deteriorate fracture toughness because they were decomposed to ferrite and fine carbides after tempering. Their simulated HAZs also had sufficient impact toughness after postweld heat treatment. These findings indicated that the reduction in C content to inhibit the formation of coarse cementite and to improve toughness and the increase in Mo and Ni to prevent the reduction in hardenability and to precipitate fine M2C carbides were useful ways to improve simultaneously the tensile and fracture properties of the HAZs as well as the base metals.

  3. Zwitterionic Group VIII transition metal initiators supported by olefin ligands

    SciTech Connect

    Bazan, Guillermo C.; Chen, Yaofeng

    2011-10-25

    A zwitterionic Group VIII transition metal complex containing the simple and relatively small 3-(arylimino)-but-1-en-2-olato ligand that catalyzes the formation of polypropylene and high molecular weight polyethylene. A novel feature of this catalyst is that the active species is stabilized by a chelated olefin adduct. The present invention also provides methods of polymerizing olefin monomers using zwitterionic catalysts, particularly polypropylene and high molecular weight polyethylene.

  4. The energetics of ordered intermetallic alloys (of the transition metals)

    SciTech Connect

    Watson, R.E.; Weinert, M.; Davenport, J.W.; Fernando, G.W.; Bennett, L.H.

    1992-10-01

    The atomically ordered phases in ordered transition metal alloys are discussed. This chapter is divided into: physical parameters controlling phase stability (Hume-Rothery, structural maps, Miedema Hamiltonian), wave functions & band theory, comment on entropy terms, cohesive energies (electron promotion energies, Hund`s rule on orbital effects), structural energies/stabilities of elemental solids, total energies and atomic positions, charge transfer (Au alloys, charge tailing), heats of formation of ordered compounds.

  5. The energetics of ordered intermetallic alloys (of the transition metals)

    SciTech Connect

    Watson, R.E.; Weinert, M.; Davenport, J.W. ); Fernando, G.W. . Dept. of Physics); Bennett, L.H. . Metallurgy Div.)

    1992-01-01

    The atomically ordered phases in ordered transition metal alloys are discussed. This chapter is divided into: physical parameters controlling phase stability (Hume-Rothery, structural maps, Miedema Hamiltonian), wave functions band theory, comment on entropy terms, cohesive energies (electron promotion energies, Hund's rule on orbital effects), structural energies/stabilities of elemental solids, total energies and atomic positions, charge transfer (Au alloys, charge tailing), heats of formation of ordered compounds.

  6. Pressure induced structural phase transition in IB transition metal nitrides compounds

    NASA Astrophysics Data System (ADS)

    Soni, Shubhangi; Kaurav, Netram; Jain, A.; Shah, S.; Choudhary, K. K.

    2015-06-01

    Transition metal mononitrides are known as refractory compounds, and they have, relatively, high hardness, brittleness, melting point, and superconducting transition temperature, and they also have interesting optical, electronic, catalytic, and magnetic properties. Evolution of structural properties would be an important step towards realizing the potential technological scenario of this material of class. In the present study, an effective interionic interaction potential (EIOP) is developed to investigate the pressure induced phase transitions in IB transition metal nitrides TMN [TM = Cu, Ag, and Au] compounds. The long range Coulomb, van der Waals (vdW) interaction and the short-range repulsive interaction upto second-neighbor ions within the Hafemeister and Flygare approach with modified ionic charge are properly incorporated in the EIOP. The vdW coefficients are computed following the Slater-Kirkwood variational method, as both the ions are polarizable. The estimated value of the phase transition pressure (Pt) and the magnitude of the discontinuity in volume at the transition pressure are consistent as compared to the reported data.

  7. Pressure induced structural phase transition in IB transition metal nitrides compounds

    SciTech Connect

    Soni, Shubhangi; Kaurav, Netram Jain, A.; Shah, S.; Choudhary, K. K.

    2015-06-24

    Transition metal mononitrides are known as refractory compounds, and they have, relatively, high hardness, brittleness, melting point, and superconducting transition temperature, and they also have interesting optical, electronic, catalytic, and magnetic properties. Evolution of structural properties would be an important step towards realizing the potential technological scenario of this material of class. In the present study, an effective interionic interaction potential (EIOP) is developed to investigate the pressure induced phase transitions in IB transition metal nitrides TMN [TM = Cu, Ag, and Au] compounds. The long range Coulomb, van der Waals (vdW) interaction and the short-range repulsive interaction upto second-neighbor ions within the Hafemeister and Flygare approach with modified ionic charge are properly incorporated in the EIOP. The vdW coefficients are computed following the Slater-Kirkwood variational method, as both the ions are polarizable. The estimated value of the phase transition pressure (Pt) and the magnitude of the discontinuity in volume at the transition pressure are consistent as compared to the reported data.

  8. Phase transition metal-crown ether coordination compounds tuned by metal ions.

    PubMed

    Ye, Qiong; Wang, Hui-Ting; Zhou, Lin; Kong, Li-Hui; Ye, Heng-Yun; Fu, Da-Wei; Zhang, Yi

    2016-01-21

    Two isostructural metal crown ether coordination compounds, (15-crown-5)(BiCl3) 1 and (15-crown-5)(SbCl3) 2, are discovered to show phase transitions above room temperature, where the phase transition temperature relates to the metal center. Compound 1 crystallizes in the chiral orthorhombic space group P212121 in the low temperature phase and undergoes a reversible phase transition around 365 K to crystallize in the polar orthorhombic space group Pna21 in the high temperature phase, accompanied by thermal and dielectric anomalies. The variable-temperature structure analyses of compound 1 show that the phase transition is rooted in the conformational change of the crown ether and the displacement of the Bi cation and Cl anion. PMID:26648559

  9. Thermodynamics of the structural transition in metal-organic frameworks.

    PubMed

    Rodriguez, J; Beurroies, I; Coulet, M-V; Fabry, P; Devic, T; Serre, C; Denoyel, R; Llewellyn, P L

    2016-03-01

    A thermodynamic study of the structural large-pore (LP) to narrow pore (NP) transition in various Metal Organic Frameworks (MOFs) is presented. First, the pressure induced transition at a constant temperature is investigated using a Tian-Calvet microcalorimeter set-up equipped with a high pressure cell. This device permits simultaneous measurements of the mechanical work and heat associated with the LP → NP transition. It is shown that MIL-53(Al) and MIL-53(Cr) have similar thermodynamic and mechanical behaviour whilst the MIL-47(V) system is characterized by much higher transition energy and mechanical work. Second, the temperature induced transition at ambient pressure is studied by means of differential scanning calorimetry (DSC) combined with X-ray absorption spectroscopy. This set-up enables one to follow simultaneously the structural changes associated with the phase transition detected by DSC. The MIL-53(Cr)-Br functionalized MOF is chosen here as a case study where both energetics and structural changes are discussed. PMID:26574728

  10. Optical properties of transition metal oxide quantum wells

    SciTech Connect

    Lin, Chungwei; Posadas, Agham; Choi, Miri; Demkov, Alexander A.

    2015-01-21

    Fabrication of a quantum well, a structure that confines the electron motion along one or more spatial directions, is a powerful method of controlling the electronic structure and corresponding optical response of a material. For example, semiconductor quantum wells are used to enhance optical properties of laser diodes. The ability to control the growth of transition metal oxide films to atomic precision opens an exciting opportunity of engineering quantum wells in these materials. The wide range of transition metal oxide band gaps offers unprecedented control of confinement while the strong correlation of d-electrons allows for various cooperative phenomena to come into play. Here, we combine density functional theory and tight-binding model Hamiltonian analysis to provide a simple physical picture of transition metal oxide quantum well states using a SrO/SrTiO{sub 3}/SrO heterostructure as an example. The optical properties of the well are investigated by computing the frequency-dependent dielectric functions. The effect of an external electric field, which is essential for electro-optical devices, is also considered.

  11. Optical properties of transition metal oxide quantum wells

    NASA Astrophysics Data System (ADS)

    Lin, Chungwei; Posadas, Agham; Choi, Miri; Demkov, Alexander A.

    2015-01-01

    Fabrication of a quantum well, a structure that confines the electron motion along one or more spatial directions, is a powerful method of controlling the electronic structure and corresponding optical response of a material. For example, semiconductor quantum wells are used to enhance optical properties of laser diodes. The ability to control the growth of transition metal oxide films to atomic precision opens an exciting opportunity of engineering quantum wells in these materials. The wide range of transition metal oxide band gaps offers unprecedented control of confinement while the strong correlation of d-electrons allows for various cooperative phenomena to come into play. Here, we combine density functional theory and tight-binding model Hamiltonian analysis to provide a simple physical picture of transition metal oxide quantum well states using a SrO/SrTiO3/SrO heterostructure as an example. The optical properties of the well are investigated by computing the frequency-dependent dielectric functions. The effect of an external electric field, which is essential for electro-optical devices, is also considered.

  12. Theory of the pairbreaking superconductor-metal transition in nanowires

    NASA Astrophysics Data System (ADS)

    Sachdev, Subir

    2009-03-01

    We present a detailed description of a zero temperature phase transition between superconducting and diffusive metallic states in very thin wires due to a Cooper pair breaking mechanism. The dissipative critical theory contains current reducing fluctuations in the guise of both quantum and thermally activated phase slips. A full cross-over phase diagram is computed via an expansion in the inverse number of complex components of the superconducting order parameter (one in the physical case). The fluctuation corrections to the electrical (σ) and thermal (κ) conductivities are determined, and we find that σ has a non-monotonic temperature dependence in the metallic phase which may be consistent with recent experimental results on ultra-narrow wires. In the quantum critical regime, the ratio of the thermal to electrical conductivity displays a linear temperature dependence and thus the Wiedemann-Franz law is obeyed, with a new universal experimentally verifiable Lorenz number. We also examined the influence of quenched disorder on the superconductor-metal transition. The self-consistent pairing eigenmodes of a quasi-one dimensional wire were determined numerically. Our results support the proposal by Hoyos et al./ (Phys. Rev. Lett. 99, 230601 (2007)) that the transition is described by the same strong disorder fixed point describing the onset of ferromagnetism in the quantum Ising model in a transverse field.

  13. Pseudopotentials for quantum Monte Carlo calculations of transition metal oxides

    NASA Astrophysics Data System (ADS)

    Krogel, Jaron; Santana, Juan; Kent, Paul; Reboredo, Fernando

    2015-03-01

    Quantum Monte Carlo calculations of transition metal oxides are partially limited by the availability of high quality pseudopotentials that are both accurate in QMC and compatible with major electronic structure codes, e.g. by not being overly hard in the standard planewave basis. Following insight gained from recent GW calculations, a set of neon core pseudopotentials with small cutoff radii have been created for the early transition metal elements Sc to Zn within the local density approximation of DFT. The pseudopotentials have been tested for energy consistency within QMC by calculating the first through fourth ionization potentials of the isolated transition metal (TM) atoms and the binding curve of each TM-O dimer. The vast majority of the ionization potentials fall within 0.3 eV of the experimental values, with exceptions occurring mainly for atoms with multiple unpaired d electrons where multireference effects are the strongest. The equilibrium bond lengths of the dimers are within 1% of experimental values and the binding energy errors are typically less than 0.3 eV. Given the uniform treatment of the core, the larger deviations occasionally observed may primarily reflect the limitations of a Slater-Jastrow trial wavefunction. This work is supported by the Materials Sciences & Engineering Division of the Office of Basic Energy Sciences, U.S. DOE. Research by PRCK was conducted at the Center for Nanophase Materials Sciences, which is a DOE Office of Science User Facility.

  14. Speed limit of the insulator-metal transition in magnetite

    NASA Astrophysics Data System (ADS)

    de Jong, S.; Kukreja, R.; Trabant, C.; Pontius, N.; Chang, C. F.; Kachel, T.; Beye, M.; Sorgenfrei, F.; Back, C. H.; Bräuer, B.; Schlotter, W. F.; Turner, J. J.; Krupin, O.; Doehler, M.; Zhu, D.; Hossain, M. A.; Scherz, A. O.; Fausti, D.; Novelli, F.; Esposito, M.; Lee, W. S.; Chuang, Y. D.; Lu, D. H.; Moore, R. G.; Yi, M.; Trigo, M.; Kirchmann, P.; Pathey, L.; Golden, M. S.; Buchholz, M.; Metcalf, P.; Parmigiani, F.; Wurth, W.; Föhlisch, A.; Schüßler-Langeheine, C.; Dürr, H. A.

    2013-10-01

    As the oldest known magnetic material, magnetite (Fe3O4) has fascinated mankind for millennia. As the first oxide in which a relationship between electrical conductivity and fluctuating/localized electronic order was shown, magnetite represents a model system for understanding correlated oxides in general. Nevertheless, the exact mechanism of the insulator-metal, or Verwey, transition has long remained inaccessible. Recently, three-Fe-site lattice distortions called trimerons were identified as the characteristic building blocks of the low-temperature insulating electronically ordered phase. Here we investigate the Verwey transition with pump-probe X-ray diffraction and optical reflectivity techniques, and show how trimerons become mobile across the insulator-metal transition. We find this to be a two-step process. After an initial 300 fs destruction of individual trimerons, phase separation occurs on a 1.5±0.2 ps timescale to yield residual insulating and metallic regions. This work establishes the speed limit for switching in future oxide electronics.

  15. Toward Rational Design of 3d Transition Metal Catalysts for CO2 Hydrogenation Based on Insights into Hydricity-Controlled Rate-Determining Steps.

    PubMed

    Mondal, Bhaskar; Neese, Frank; Ye, Shengfa

    2016-06-01

    Carbon dioxide functionalization attracts much interest due to the current environmental and energy challenges. Our earlier work (Mondal, B.; Neese, F.; Ye, S. Inorg. Chem. 2015, 54, 7192-7198) demonstrated that CO2 hydrogenation mediated by base metal catalysts [M(H)(η(2)-H2)(PP3(Ph))](n+) (M = Co(III) and Fe(II), n = 1, 2; PP3(Ph) = tris(2-(diphenylphosphino)phenyl)phosphine) features discrete rate-determining steps (RDSs). Specifically, the reaction with [Co(III)(H)(η(2)-H2)(PP3(Ph))](2+) passes through a hydride-transfer RDS, whereas the conversion with [Fe(II)(H)(η(2)-H2)(PP3(Ph))](+) traverses a H2-splitting RDS. More importantly, we found that the nature and barrier of the RDS likely correlate with the hydride affinity or hydricity of the dihydride intermediate [M(H)2(PP3(Ph))]((n-1)+) generated by H2-splitting. In the present contribution, following this notion we design a series of potential Fe(II) and Co(III) catalysts, for which the respective dihydride species possess differential hydricities, and computationally investigated their reactivity toward CO2 hydrogenation. Our results reveal that lowering the hydrictiy of [Co(III)(H)2(PP3(Ph))](+) by introducing anionic anchors in PP3(Ph) dramatically decreases the hydride-transfer RDS barrier, as shown for the enhanced reactivity of [Co(H)(η(2)-H2)(CP3(Ph))](+) and [Co(H)(η(2)-H2)(SiP3(Ph))](+) (CP3(Ph) = tris(2-(diphenylphosphino)phenyl)methyl, SiP3(Ph) = tris(2-(diphenylphosphino)phenyl)silyl), while the same ligand modification increases the H2-splitting RDS barriers for [Fe(H)(η(2)-H2)(CP3(Ph))] and [Fe(H)(η(2)-H2)(SiP3(Ph))] relative to that for [Fe(H)(η(2)-H2)(PP3(Ph))](+). Conversely, upon increasing the hydricity of [Fe(II)(H)2(PP3(Ph))] by adding an electron-withdrawing group to PP3(Ph), the transformation with [Fe(H)(η(2)-H2)(PP3(PhNO2))](+) (PP3(PhNO2) = tris(2-(diphenylphosphino)-4-nitrophenyl)phosphine) is predicted to encounter a lower barrier for H2-splitting and a higher barrier for

  16. Transition-metal prion protein attachment: Competition with copper

    NASA Astrophysics Data System (ADS)

    Hodak, Miroslav; Bernholc, Jerry

    2012-02-01

    Prion protein, PrP, is a protein capable of binding copper ions in multiple modes depending on their concentration. Misfolded PrP is implicated in a group of neurodegenerative diseases, which include ``mad cow disease'' and its human form, variant Creutzfeld-Jacob disease. An increasing amount of evidence suggests that attachment of non-copper metal ions to PrP triggers transformations to abnormal forms similar to those observed in prion diseases. In this work, we use hybrid Kohn-Sham/orbital-free density functional theory simulations to investigate copper replacement by other transition metals that bind to PrP, including zinc, iron and manganese. We consider all known copper binding modes in the N-terminal domain of PrP. Our calculations identify modes most susceptible to copper replacement and reveal metals that can successfully compete with copper for attachment to PrP.

  17. Thermophysical Property Measurements of Silicon-Transition Metal Alloys

    NASA Technical Reports Server (NTRS)

    Banish, R. Michael; Erwin, William R.; Sansoucie, Michael P.; Lee, Jonghyun; Gave, Matthew A.

    2014-01-01

    Metals and metallic alloys often have high melting temperatures and highly reactive liquids. Processing reactive liquids in containers can result in significant contamination and limited undercooling. This is particularly true for molten silicon and it alloys. Silicon is commonly termed "the universal solvent". The viscosity, surface tension, and density of several silicon-transition metal alloys were determined using the Electrostatic Levitator system at the Marshall Space Flight Center. The temperature dependence of the viscosity followed an Arrhenius dependence, and the surface tension followed a linear temperature dependence. The density of the melts, including the undercooled region, showed a linear behavior as well. Viscosity and surface tension values were obtain for several of the alloys in the undercooled region.

  18. Method for treating rare earth-transition metal scrap

    DOEpatents

    Schmidt, Frederick A.; Peterson, David T.; Wheelock, John T.; Jones, Lawrence L.

    1992-12-29

    Rare earth-transition metal (e.g., iron) scrap (e.g., Nd-Fe-B scrap) is flux (slag) remelted to reduce tramp non-metallic impurities, such as oxygen and nitrogen, and metallic impurities, such as Li, Na, Al, etc., picked up by the scrap from previous fabrication operations. The tramp impurities are reduced to concentrations acceptable for reuse of the treated alloy in the manufacture of end-use articles, such as permanent magnets. The scrap is electroslag or inductoslag melted using a prefused, rare earth fluoride-bearing flux of CaF.sub.2, CaCl.sub.2 or mixtures thereof or the slag resulting from practice of the thermite reduction process to make a rare earth-iron alloy.

  19. Method for treating rare earth-transition metal scrap

    DOEpatents

    Schmidt, F.A.; Peterson, D.T.; Wheelock, J.T.; Jones, L.L.

    1992-12-29

    Rare earth-transition metal (e.g., iron) scrap (e.g., Nd-Fe-B scrap) is flux (slag) remelted to reduce tramp non-metallic impurities, such as oxygen and nitrogen, and metallic impurities, such as Li, Na, Al, etc., picked up by the scrap from previous fabrication operations. The tramp impurities are reduced to concentrations acceptable for reuse of the treated alloy in the manufacture of end-use articles, such as permanent magnets. The scrap is electroslag or inductoslag melted using a rare earth fluoride-bearing flux of CaF[sub 2], CaCl[sub 2] or mixtures thereof or the slag resulting from practice of the thermite reduction process to make a rare earth-iron alloy. 3 figs.

  20. A Transition to Metallic Hydrogen: Evidence of the Plasma Phase Transition

    NASA Astrophysics Data System (ADS)

    Silvera, Isaac; Zaghoo, Mohamed; Salamat, Ashkan

    The insulator-metal transition in hydrogen is one of the most outstanding problems in condensed matter physics. The high-pressure metallic phase is now predicted to be liquid atomic from T =0 K to very high temperatures. We have conducted measurements of optical properties of hot dense hydrogen in the region of 1.1-1.7 Mbar and up to 2200 K in a diamond anvil cell using pulsed laser heating of the sample. We present evidence in two forms: a plateau in the heating curves (average laser power vs temperature) characteristic of a first-order phase transition with latent heat, and changes in transmittance and reflectance characteristic of a metal for temperatures above the plateau temperature. For thick films the reflectance saturates at ~0.5. The phase line of this transition has a negative slope in agreement with theories of the so-called plasma phase transition. The NSF, Grant DMR-1308641, the DOE Stockpile Stewardship Academic Alliance Program, Grant DE-FG52-10NA29656, and NASA Earth and Space Science Fellowship Program, Award NNX14AP17H supported this research.

  1. Polaronic Transport in Phosphate Glasses Containing Transition Metal Ions

    NASA Astrophysics Data System (ADS)

    Henderson, Mark

    The goal of this dissertation is to characterize the basic transport properties of phosphate glasses containing various amounts of TIs and to identify and explain any electronic phase transitions which may occur. The P2 O5-V2O5-WO3 (PVW) glass system will be analyzed to find the effect of TI concentration on conduction. In addition, the effect of the relative concentrations of network forming ions (SiO2 and P2O5) on transport will be studied in the P2O5-SiO2-Fe2O 3 (PSF) system. Also presented is a numerical study on a tight-binding model adapted for the purposes of modelling Gaussian traps, mimicking TI's, which are arranged in an extended network. The results of this project will contribute to the development of fundamental theories on the electronic transport in glasses containing mixtures of transition oxides as well as those containing multiple network formers without discernible phase separation. The present study on the PVW follows up on previous investigation into the effect on mixed transition ions in oxide glasses. Past research has focused on glasses containing transition metal ions from the 3d row. The inclusion of tungsten, a 5d transition metal, adds a layer of complexity through the mismatch of the energies of the orbitals contributing to localized states. The data have indicated that a transition reminiscent of a metal-insulator transition (MIT) occurs in this system as the concentration of tungsten increases. As opposed to some other MIT-like transitions found in phosphate glass systems, there seems to be no polaron to bipolaron conversion. Instead, the individual localization parameter for tungsten noticeably decreases dramatically at the transition point as well as the adiabaticity. Another distinctive feature of this project is the study of the PSF system, which contains two true network formers, phosphorous pentoxide (P2O 5) and silicon dioxide (SiO2). It is not usually possible to do a reliable investigation of the conduction properties of

  2. Metal to Insulator Quantum-Phase Transition in Few-Layered ReS₂.

    PubMed

    Pradhan, Nihar R; McCreary, Amber; Rhodes, Daniel; Lu, Zhengguang; Feng, Simin; Manousakis, Efstratios; Smirnov, Dmitry; Namburu, Raju; Dubey, Madan; Walker, Angela R Hight; Terrones, Humberto; Terrones, Mauricio; Dobrosavljevic, Vladimir; Balicas, Luis

    2015-12-01

    In ReS2, a layer-independent direct band gap of 1.5 eV implies a potential for its use in optoelectronic applications. ReS2 crystallizes in the 1T'-structure, which leads to anisotropic physical properties and whose concomitant electronic structure might host a nontrivial topology. Here, we report an overall evaluation of the anisotropic Raman response and the transport properties of few-layered ReS2 field-effect transistors. We find that ReS2 exfoliated on SiO2 behaves as an n-type semiconductor with an intrinsic carrier mobility surpassing μ(i) ∼ 30 cm(2)/(V s) at T = 300 K, which increases up to ∼350 cm(2)/(V s) at 2 K. Semiconducting behavior is observed at low electron densities n, but at high values of n the resistivity decreases by a factor of >7 upon cooling to 2 K and displays a metallic T(2)-dependence. This suggests that the band structure of 1T'-ReS2 is quite susceptible to an electric field applied perpendicularly to the layers. The electric-field induced metallic state observed in transition metal dichalcogenides was recently claimed to result from a percolation type of transition. Instead, through a scaling analysis of the conductivity as a function of T and n, we find that the metallic state of ReS2 results from a second-order metal-to-insulator transition driven by electronic correlations. This gate-induced metallic state offers an alternative to phase engineering for producing ohmic contacts and metallic interconnects in devices based on transition metal dichalcogenides. PMID:26599563

  3. Giant, ultrafast optical switching based on an Insulator-to-MetalTransition in VO2 Nano-particles: Photo-activation of shape-controlledplasmons at 1.55 mu-m

    SciTech Connect

    Rini, M.; Cavalleri, A.; Schoenlein, R.W.; Lopez, R.; Feldman,C.; Haglund, R.; Boatner, L.A.; Haynes, T.E.

    2004-07-01

    A new generation of devices where the electronic, optical or magnetic state of a system can be controlled optically on the ultrafast timescale is one of the most compelling technological ramifications of the rapidly advancing field of strongly correlated electrons. However, for real-world applications it is also necessary to incorporate these compounds in appropriate environments (e.g. optical fibers or silicon-based electronics), to ensure compatibility with existing technologies (e.g. telecom wavelengths), room temperature operation and limited power densities. Here, we report on the study of the photo-activated optical switching in nanorods of strongly correlated VO{sub 2}. The particles are grown by ion-implantation and self-assembly within a Silica matrix or an optical fiber, operate at room temperature and can be switched between the insulating and metallic phase within less than 100 fs. The energy threshold to achieve switching corresponds to approximately 500 pJ within the core of a single mode fiber and is compatible with current diode technologies. Tailoring of the spherical/cylindrical geometry results in control of the spectral response of the system, which is dominated by the impulsive formation of a surface plasmon upon the insulator-to-metal transition. The response at the technologically important 1.55 {micro}m wavelength is in this way maximized.

  4. Metal-insulator transition in trans-polyacetylene

    NASA Astrophysics Data System (ADS)

    Conwell, E. M.; Mizes, H. A.; Jeyadev, S.

    1989-07-01

    We have calculated the band structure for a chain of doped trans-polyacetylene using the electronic part of the Su-Schrieffer-Heeger Hamiltonian plus the Coulomb potential arising from ions and charged solitons surrounding the chain. The lattice structure used was that determined by x rays for Na-doped polyacetylene. To agree with a number of experimental observations the donated electrons were taken to be in soliton states at all dopant concentrations. In obtaining the potential of a point charge on a chain in the metallic state, the confinement of the free electrons to a chain was taken into account. Because screening depends on the calculated energy levels, specifically on the density of states at the Fermi energy, η(EF), in the metallic state, which, in turn, depend on the potential used to obtain them, self-consistency was required in the calculations. The energy-level structure was found to depend strongly on the ion spacing, conveniently measured in terms of the average spacing a of C-H's along the chain. For ion spacing 5a, characteristic of the Na-ion-rich regions up to an average dopant concentration of ~6%, the chain remained semiconducting. For ion spacing 4a, which appears to characterize the next phase for Na doping, metallic behavior was found for a doped chain length of ~100 sites or more. Self-consistency was fulfilled with η(EF) equal to the value obtained from the saturation spin susceptibility in the metallic state. In addition to sufficiently long chains that the level spacing is comparable to kT, the metal-insulator transition is found to require considerable overlap of electron wave functions on adjacent solitons and a fairly deep potential well. The transition is best described as a Mott transition. Our model predicts that a sample in the metallic state at room temperature becomes semiconducting at lower temperature. Evidence for this is found in the temperature variation of the spin susceptibility and of ESR linewidth. It is argued that

  5. Disorder and Metal-Insulator Transitions in Weyl Semimetals.

    PubMed

    Chen, Chui-Zhen; Song, Juntao; Jiang, Hua; Sun, Qing-feng; Wang, Ziqiang; Xie, X C

    2015-12-11

    The Weyl semimetal (WSM) is a newly proposed quantum state of matter. It has Weyl nodes in bulk excitations and Fermi arc surface states. We study the effects of disorder and localization in WSMs and find three novel phase transitions. (i) Two Weyl nodes near the Brillouin zone boundary can be annihilated pairwise by disorder scattering, resulting in the opening of a topologically nontrivial gap and a transition from a WSM to a three-dimensional quantum anomalous Hall state. (ii) When the two Weyl nodes are well separated in momentum space, the emergent bulk extended states can give rise to a direct transition from a WSM to a 3D diffusive anomalous Hall metal. (iii) Two Weyl nodes can emerge near the zone center when an insulating gap closes with increasing disorder, enabling a direct transition from a normal band insulator to a WSM. We determine the phase diagram by numerically computing the localization length and the Hall conductivity, and propose that the novel phase transitions can be realized on a photonic lattice. PMID:26705648

  6. Mixed-Ligand Approach to Changing the Metal Ratio in Bismuth-Transition Metal Heterometallic Precursors.

    PubMed

    Lieberman, Craig M; Wei, Zheng; Filatov, Alexander S; Dikarev, Evgeny V

    2016-04-18

    A new series of heteroleptic bismuth-transition metal β-diketonates [BiM(hfac)3(thd)2] (M = Mn (1), Co (2), and Ni (3); hfac = hexafluoroacetylacetonate, thd = tetramethylheptanedionate) with Bi:M = 1:1 ratio have been synthesized by stoichiometric reactions between homometallic reagents [Bi(III)(hfac)3] and [M(II)(thd)2]. On the basis of analysis of the metal-ligand interactions in heterometallic structures, the title compounds were formulated as ion-pair {[Bi(III)(thd)2](+)[M(II)(hfac)3](-)} complexes. The direct reaction between homometallic reagents proceeds with a full ligand exchange between main group and transition metal centers, yielding dinuclear heterometallic molecules. In heteroleptic molecules 1-3, the Lewis acidic, coordinatively unsaturated Bi(III) centers are chelated by two bulky, electron-donating thd ligands and maintain bridging interactions with three oxygen atoms of small, electron-withdrawing hfac groups that chelate the neighboring divalent transition metals. Application of the mixed-ligand approach allows one to change the connectivity pattern within the heterometallic assembly and to isolate highly volatile precursors with the proper Bi:M = 1:1 ratio. The mixed-ligand approach employed in this work opens broad opportunities for the synthesis of heterometallic (main group-transition metal) molecular precursors with specific M:M' ratio in the case when homoleptic counterparts either do not exist or afford products with an incorrect metal:metal ratio for the target materials. Heteroleptic complexes obtained in the course of this study represent prospective single-source precursors for the low-temperature preparation of multiferroic perovskite-type oxides. PMID:27054922

  7. Heterobimetallic coordination polymers involving 3d metal complexes and heavier transition metals cyanometallates

    SciTech Connect

    Peresypkina, Eugenia V.; Samsonenko, Denis G.; Vostrikova, Kira E.

    2015-04-15

    The results of the first steps in the design of coordination polymers based on penta- and heptacyanometallates of heavier d transitions metals are presented. The 2D structure of the coordination polymers: [(Mn(acacen)){sub 2}Ru(NO)(CN){sub 5}]{sub n} and two complexes composed of different cyanorhenates, [Ni(cyclam)]{sub 2}[ReO(OH)(CN){sub 4}](ClO{sub 4}){sub 2}(H{sub 2}O){sub 1.25} and [Cu(cyclam)]{sub 2}[Re(CN){sub 7}](H{sub 2}O){sub 12}, was confirmed by single crystal XRD study, the rhenium oxidation state having been proved by the magnetic measurements. An amorphism of [M(cyclam)]{sub 3}[Re(CN){sub 7}]{sub 2} (M=Ni, Cu) polymers does not allow to define strictly their dimensionality and to model anisotropic magnetic behavior of the compounds. However, with high probability a honey-comb like layer structure could be expected for [M(cyclam)]{sub 3}[Re(CN){sub 7}]{sub 2} complexes, studied in this work, because such an arrangement is the most common among the bimetallic assemblies of hexa- and octacyanometallates with a ratio [M(cyclam)]/[M(CN){sub n}]=3/2. For the first time was prepared and fully characterized a precursor (n-Bu{sub 4}N){sub 2}[Ru(NO)(CN){sub 5}], soluble in organic media. - Graphical abstract: The very first results in the design of 2D coordination polymers based on penta- and heptacyanometallates of 4d and5d transitions metals are presented. - Highlights: • Design of coordination polymers based on penta- and heptacyanometallates. • New Ru and Re cyanide based heterobimetallic coordination complexes. • Hydrolysis and ox/red processes involving [Re(CN){sub 7}]{sup 3+} during crystallization. • High magnetic anisotropy of [M(cyclam)]{sub 3}[Re(CN){sub 7}]{sub 2}(H{sub 2}O){sub n}, M=Cu, Ni, complexes.

  8. Effect of Transition Metals on Polysialic Acid Structure and Functions.

    PubMed

    Murthy, Raghavendra Vasudeva; Bharate, Priya; Gade, Madhuri; Sangabathuni, Sivakoti; Kikkeri, Raghavendra

    2016-04-01

    Polysialic acid (PSA) is one of the most abundant glycopolymer present in embryonic brain, and it is known to be involved in key roles such as plasticity in the central nervous system, cell adhesion, migration and localization of neurotrophins. However, in adult brain, its expression is quite low. The exception to this is in Alzheimer's disease (AD) brain, where significantly increased levels of polysilylated neural cell adhesion molecule (PSA-NCAM) have been reported. Here, we confirm the role of PSA as a metal chelator, allowing it to decrease cytotoxicity caused by high levels of transition metals, commonly found in AD brain, and as a regulator of cell behavior. UV-visible (UV-vis) and circular dichroism (CD) spectroscopy, atomic force microscopy (AFM), and isothermal titration calorimetry (ITC) techniques were used to investigate the assembly of PSA-metals complexes. These PSA-metal complexes exhibited less toxicity compared to free metal ions, and in particular, the PSA-Cu(2+) complex synergistically promoted neurite outgrowth in PC12 cells. PMID:26990355

  9. Alternative Kondo breakdown mechanism: Orbital-selective orthogonal metal transition

    NASA Astrophysics Data System (ADS)

    Zhong, Yin; Liu, Ke; Wang, Yong-Qiang; Luo, Hong-Gang

    2012-09-01

    In a recent paper of Nandkishore, Metlitski, and Senthil [Phys. Rev. B1098-012110.1103/PhysRevB.86.045128 86, 045128 (2012)], a concept of orthogonal metal has been introduced to reinterpret the disordered state of slave-spin representation in the Hubbard model as an exotic gapped metallic state. We extend this concept to study the corresponding quantum phase transition in the extended Anderson lattice model. It is found that the disordered state of slave spins in this model is an orbital-selective orthogonal metal, a generalization of the concept of the orthogonal metal in the Hubbard model. The quantum critical behaviors are multiscale and dominated by a z=3 and z=2 critical modes in the high- and low-temperature regime, respectively. Such behaviors are obviously in contrast to the naive expectation in the Hubbard model. The result provides alternative Kondo breakdown mechanism for heavy fermion compounds underlying the physics of the orbital-selective orthogonal metal in the disordered state, which is different from the conventional Kondo breakdown mechanism with the fractionalized Fermi-liquid picture. This work is expected to be useful in understanding the quantum criticality happening in some heavy fermion materials and other related strongly correlated systems.

  10. Thermodynamics of Metal Composites Based on Polyvinylchloride

    NASA Astrophysics Data System (ADS)

    Kolupaev, B. B.; Lyashuk, T. G.; Kolupaev, B. S.

    2014-03-01

    We present the results of experimental investigations of the thermodynamic properties of composites based on polyvinylchloride and copper nanoparticles obtained by electrical explosion of the conductor. It has been established that the thermodynamic potentials H and G in determining the system parameters (s, T, p, V) depend nonlinearly on the temperature and content of the filler. β- and α-relaxation transitions as a general phenomenon characteristic of the fluctuation structure of polyvinylchloride are observed thereby. The introduction of a nanodispersed metal filler into polyvinylchloride increases the amount of activation energy and the time of "settled" life of the structural elements, changing the thermodynamic stability of the composite.

  11. Insulator-metal transition of highly compressed carbon disulfide

    SciTech Connect

    Dias, Ranga P.; Yoo, Choong-Shik; Kim, Minseob; Tse, John S.

    2012-04-24

    We present integrated spectral, structural, resistance, and theoretical evidences for simple molecular CS{sub 2} transformations to an insulating black polymer with threefold carbon atoms at 9 GPa, then to a semiconducting polymer above 30 GPa, and finally to a metallic solid above 50 GPa. The metallic phase is a highly disordered three-dimensional network structure with fourfold carbon atoms at the carbon-sulfur distance of {approx}1.70 {angstrom}. Based on first-principles calculations, we present two plausible structures for the metallic phase: {alpha}-chalcopyrite and tridymite, both of which exhibit metallic ground states and disordered diffraction features similar to that measured. We also present the phase and chemical transformation diagram for carbon disulfide, showing a large stability field of the metallic phase to 100 GPa and 800 K.

  12. Comparative study of the synthesis of layered transition metal molybdates

    SciTech Connect

    Mitchell, S.; Gomez-Aviles, A.; Gardner, C.; Jones, W.

    2010-01-15

    Mixed metal oxides (MMOs) prepared by the mild thermal decomposition of layered double hydroxides (LDHs) differ in their reactivity on exposure to aqueous molybdate containing solutions. In this study, we investigate the reactivity of some T-Al containing MMOs (T=Co, Ni, Cu or Zn) towards the formation of layered transition metal molybdates (LTMs) possessing the general formula AT{sub 2}(OH)(MoO{sub 4}){sub 2}.H{sub 2}O, where A=NH{sub 4}{sup +}, Na{sup +} or K{sup +}. The phase selectivity of the reaction was studied with respect to the source of molybdate, the ratio of T to Mo and the reaction pH. LTMs were obtained on reaction of Cu-Al and Zn-Al containing MMOs with aqueous solutions of ammonium heptamolybdate. Rehydration of these oxides in the presence of sodium or potassium molybdate yielded a rehydrated LDH phase as the only crystalline product. The LTM products obtained by the rehydration of MMO precursors were compared with LTMs prepared by direct precipitation from the metal salts in order to study the influence of preparative route on their chemical and physical properties. Differences were noted in the composition, morphology and thermal properties of the resulting products. - Graphical abstract: Mixed metal oxides (MMOs) derived from layered double hydroxide precursors differ in their reactivity on exposure to aqueous molybdate containing solutions. We investigate the influence of the molybdate source, the rehydration pH and the ratio of T/Mo on the reactivity of some T-Al containing MMOs (T=Co, Ni, Cu or Zn) towards the formation of layered transition metal molybdates of general formula AT{sub 2}(OH)(MoO{sub 4}){sub 2}.H{sub 2}O (where A{sup +}=NH{sub 4}{sup +}, K{sup +} or Na{sup +}).

  13. Electronic Principles Governing the Stability and Reactivity of Ligated Metal and Silicon Encapsulated Transition Metal Clusters

    NASA Astrophysics Data System (ADS)

    Abreu, Marissa Baddick

    A thorough understanding of the underlying electronic principles guiding the stability and reactivity of clusters has direct implications for the identification of stable clusters for incorporation into clusters-assembled materials with tunable properties. This work explores the electronic principles governing the stability and reactivity of two types of clusters: ligated metal clusters and silicon encapsulated transition metal clusters. In the first case, the reactivity of iodine-protected aluminum clusters, Al13Ix - (x=0-4) and Al14Iy- (y=0-5), with the protic species methanol was studied. The symmetrical ground states of Al13Ix- showed no reactivity with methanol but reactivity was achieved in a higher energy isomer of Al 13I2- with iodines on adjacent aluminum atoms -- complementary Lewis acid-base active sites were induced on the opposite side of the cluster capable of breaking the O-H bond in methanol. Al 14Iy- (y=2-5) react with methanol, but only at the ligated adatom site. Reaction of methanol with Al14 - and Al14I- showed that ligation of the adatom was necessary for the reaction to occur there -- revealing the concept of a ligand-activated adatom. In the second case, the study focused heavily on CrSi12, a silicon encapsulated transition metal cluster whose stability and the reason for that stability has been debated heavily in the literature. Calculations of the energetic properties of CrSi n (n=6-16) revealed both CrSi12 and CrSi14 to have enhanced stability relative to other clusters; however CrSi12 lacks all the traditional markers of a magic cluster. Molecular orbital analysis of each of these clusters showed the CNFEG model to be inadequate in describing their stability. Because the 3dz2 orbital of Cr is unfilled in CrSi12, this cluster has only 16 effective valence electrons, meaning that the 18-electron rule is not applicable. The moderate stability of CrSi 12 can be accounted for by the crystal-field splitting of the 3d orbitals, which pushes the

  14. Instability of Nano- and Microscale Liquid Metal Filaments: Transition from Single Droplet Collapse to Multidroplet Breakup.

    PubMed

    Hartnett, C A; Mahady, K; Fowlkes, J D; Afkhami, S; Kondic, L; Rack, P D

    2015-12-22

    We carry out experimental and numerical studies to investigate the collapse and breakup of finite size, nano- and microscale, liquid metal filaments supported on a substrate. We find the critical dimensions below which filaments do not break up but rather collapse to a single droplet. The transition from collapse to breakup can be described as a competition between two fluid dynamic phenomena: the capillary driven end retraction and the Rayleigh-Plateau type instability mechanism that drives the breakup. We focus on the unique spatial and temporal transition region between these two phenomena using patterned metallic thin film strips and pulsed-laser-induced dewetting. The experimental results are compared to an analytical model proposed by Driessen et al. and modified to include substrate interactions. In addition, we report the results of numerical simulations based on a volume-of-fluid method to provide additional insight and highlight the importance of liquid metal resolidification, which reduces inertial effects. PMID:26595519

  15. Method of synthesizing bulk transition metal carbide, nitride and phosphide catalysts

    DOEpatents

    Choi, Jae Soon; Armstrong, Beth L; Schwartz, Viviane

    2015-04-21

    A method for synthesizing catalyst beads of bulk transmission metal carbides, nitrides and phosphides is provided. The method includes providing an aqueous suspension of transition metal oxide particles in a gel forming base, dropping the suspension into an aqueous solution to form a gel bead matrix, heating the bead to remove the binder, and carburizing, nitriding or phosphiding the bead to form a transition metal carbide, nitride, or phosphide catalyst bead. The method can be tuned for control of porosity, mechanical strength, and dopant content of the beads. The produced catalyst beads are catalytically active, mechanically robust, and suitable for packed-bed reactor applications. The produced catalyst beads are suitable for biomass conversion, petrochemistry, petroleum refining, electrocatalysis, and other applications.

  16. Laser opto-acoustic study of phase transitions in metals confined by transparent dielectric

    NASA Astrophysics Data System (ADS)

    Ivochkin, A. Yu.; Kaptilniy, A. G.; Karabutov, A. A.; Ksenofontov, D. M.

    2012-07-01

    First-order phase transitions in metal induced by nanosecond laser pulse are studied here. The metal surface is irradiated through a layer of transparent dielectric—an optical glass. Such confinement considerably increases the efficiency of pressure generation at the metal surface. This technique allows to obtain near-critical states of metals—with temperatures ˜104 K and pressures ˜104 atm with table-top equipment. At the same time the glass prevents the ablation plume formation—so the surface temperature can be measured using thermal radiation data. An experimental setup for simultaneous measurements of pressure, temperature and reflectivity was assembled based on the elaborated method of experimental research. The processes of melting of lead and boiling of mercury were studied. The onset of the phase transition process led to a considerable tightening of the pressure pulse. A substantial drop of surface reflectivity due to increase of temperature and decrease of density was observed.

  17. Instability of nano- and microscale liquid metal filaments: Transition from single droplet collapse to multidroplet breakup

    SciTech Connect

    Hartnett, Chris A.; Mahady, Kyle; Fowlkes, Jason Davidson; Afkhami, Shahriar; Rack, P. D.; Kondic, L.

    2015-11-23

    We carry out experimental and numerical studies to investigate the collapse and breakup of finite size, nano- and microscale, liquid metal filaments supported on a substrate. We find the critical dimensions below which filaments do not break up but rather collapse to a single droplet. The transition from collapse to breakup can be described as a competition between two fluid dynamic phenomena: the capillary driven end retraction and the Rayleigh–Plateau type instability mechanism that drives the breakup. We focus on the unique spatial and temporal transition region between these two phenomena using patterned metallic thin film strips and pulsed-laser-induced dewetting. The experimental results are compared to an analytical model proposed by Driessen et al. and modified to include substrate interactions. Additionally, we report the results of numerical simulations based on a volume-of-fluid method to provide additional insight and highlight the importance of liquid metal resolidification, which reduces inertial effects.

  18. Spin-exchange interaction between transition metals and metalloids in soft-ferromagnetic metallic glasses.

    PubMed

    Das, Santanu; Choudhary, Kamal; Chernatynskiy, Aleksandr; Choi Yim, Haein; Bandyopadhyay, Asis K; Mukherjee, Sundeep

    2016-06-01

    High-performance magnetic materials have immense industrial and scientific importance in wide-ranging electronic, electromechanical, and medical device technologies. Metallic glasses with a fully amorphous structure are particularly suited for advanced soft-magnetic applications. However, fundamental scientific understanding is lacking for the spin-exchange interaction between metal and metalloid atoms, which typically constitute a metallic glass. Using an integrated experimental and molecular dynamics approach, we demonstrate the mechanism of electron interaction between transition metals and metalloids. Spin-exchange interactions were investigated for a Fe-Co metallic glass system of composition [(Co1-x Fe x )0.75B0.2Si0.05]96Cr4. The saturation magnetization increased with higher Fe concentration, but the trend significantly deviated from simple rule of mixtures. Ab initio molecular dynamics simulation was used to identify the ferromagnetic/anti-ferromagnetic interaction between the transition metals and metalloids. The overlapping band-structure and density of states represent 'Stoner type' magnetization for the amorphous alloys in contrast to 'Heisenberg type' in crystalline iron. The enhancement of magnetization by increasing iron was attributed to the interaction between Fe 3d and B 2p bands, which was further validated by valence-band study. PMID:27143686

  19. Spin-exchange interaction between transition metals and metalloids in soft-ferromagnetic metallic glasses

    NASA Astrophysics Data System (ADS)

    Das, Santanu; Choudhary, Kamal; Chernatynskiy, Aleksandr; Choi Yim, Haein; Bandyopadhyay, Asis K.; Mukherjee, Sundeep

    2016-06-01

    High-performance magnetic materials have immense industrial and scientific importance in wide-ranging electronic, electromechanical, and medical device technologies. Metallic glasses with a fully amorphous structure are particularly suited for advanced soft-magnetic applications. However, fundamental scientific understanding is lacking for the spin-exchange interaction between metal and metalloid atoms, which typically constitute a metallic glass. Using an integrated experimental and molecular dynamics approach, we demonstrate the mechanism of electron interaction between transition metals and metalloids. Spin-exchange interactions were investigated for a Fe–Co metallic glass system of composition [(Co1‑x Fe x )0.75B0.2Si0.05]96Cr4. The saturation magnetization increased with higher Fe concentration, but the trend significantly deviated from simple rule of mixtures. Ab initio molecular dynamics simulation was used to identify the ferromagnetic/anti-ferromagnetic interaction between the transition metals and metalloids. The overlapping band-structure and density of states represent ‘Stoner type’ magnetization for the amorphous alloys in contrast to ‘Heisenberg type’ in crystalline iron. The enhancement of magnetization by increasing iron was attributed to the interaction between Fe 3d and B 2p bands, which was further validated by valence-band study.

  20. Bonding Model for Transition Metal and Rare Earth Monoxides and Laser Spectroscopy of Nickel-Oxide

    NASA Astrophysics Data System (ADS)

    Srdanov, Vojislav I.

    We discovered that, for the transition metal and the rare earth monoxide series, the sum of the ionization potential of the metal, the energy of the lowest ( ...np) configuration of the metal ion and the thermochemical dissociation energy of the molecule adds up to a constant number. The correlation is particularly striking for the rare earth monoxides where the standard deviation is less than 1%. Based on this correlation we developed a new bonding scheme common for both the transition metal and rare earth monoxides. We propose that the bonding is invariant within the series and consists of an ionic and a covalent contribution. In our model a covalent contribution to the bonding of the inner-core d and f orbitals is negligible. This is in contrast to the current paradigm regarding the significant role of the d orbitals in the bonding in the first and second row transition metal oxides. Our model also appears to be in conflict with the M^{2+} O^{2-} ligand-field bonding model currently accepted for the rare earth monoxides. Based on the empirical correlation and the proposed bonding mechanism, however, we give a number of predictions regarding yet unmeasured fundamental quantities of some of the oxides such as permanent dipole moments, dissociation energies and equilibrium bond distances. We also present the results of the first high resolution laser spectroscopic study of the NiO molecule. Several bands in the green spectral region were found to originate from the ground state of NiO; their analysis allowed us to determine the following fundamental parameters: Ground state symmetry: ^3Sigma^-; Vibrational frequency: omega_{ rm e} = 8.39.1 cm^{ -1}; Equilibrium distance: r_ {rm e} = 1.627 A. With this work the determination of the ground state parameters for the first row transition metal oxides is now complete.

  1. Roles of transition metals interchanging with lithium in electrode materials.

    PubMed

    Kawaguchi, Tomoya; Fukuda, Katsutoshi; Tokuda, Kazuya; Sakaida, Masashi; Ichitsubo, Tetsu; Oishi, Masatsugu; Mizuki, Jun'ichiro; Matsubara, Eiichiro

    2015-06-01

    Roles of antisite transition metals interchanging with Li atoms in electrode materials of Li transition-metal complex oxides were clarified using a newly developed direct labeling method, termed powder diffraction anomalous fine structure (P-DAFS) near the Ni K-edge. We site-selectively investigated the valence states and local structures of Ni in Li0.89Ni1.11O2, where Ni atoms occupy mainly the NiO2 host-layer sites and partially the interlayer Li sites in-between the host layers, during electrochemical Li insertion/extraction in a lithium-ion battery (LIB). The site-selective X-ray near edge structure evaluated via the P-DAFS method revealed that the interlayer Ni atoms exhibited much lower electrochemical activity as compared to those at the host-layer site. Furthermore, the present analyses of site-selective extended X-ray absorption fine structure performed using the P-DAFS method indicates local structural changes around the residual Ni atoms at the interlayer space during the initial charge; it tends to gather to form rock-salt NiO-like domains around the interlayer Ni. The presence of the NiO-like domains in the interlayer space locally diminishes the interlayer distance and would yield strain energy because of the lattice mismatch, which retards the subsequent Li insertion both thermodynamically and kinetically. Such restrictions on the Li insertion inevitably make the NiO-like domains electrochemically inactive, resulting in an appreciable irreversible capacity after the initial charge but an achievement of robust linkage of neighboring NiO2 layers that tend to be dissociated without the Li occupation. The P-DAFS characterization of antisite transition metals interchanging with Li atoms complements the understanding of the detailed charge-compensation and degradation mechanisms in the electrode materials. PMID:25959625

  2. Stacking dependent electronic structures of transition metal dichalcogenides heterobilayer

    NASA Astrophysics Data System (ADS)

    Lee, Yea-Lee; Park, Cheol-Hwan; Ihm, Jisoon

    The systematic study of the electronic structures and optical properties of the transition metal dichalcogenides (TMD) heterobilayers can significantly improve the designing of new electronic and optoelectronic devices. Here, we theoretically study the electronic structures and optical properties of TMD heterobilayers using the first-principles methods. The band structures of TMD heterobilayer are shown to be determined by the band alignments of the each layer, the weak interlayer interactions, and angle dependent stacking patterns. The photoluminescence spectra are investigated using the calculated band structures, and the optical absorption spectra are examined by the GW approximations including the electron-hole interaction through the solution of the Bethe-Salpeter equation. It is expected that the weak interlayer interaction gives rise to the substantial interlayer optical transition which will be corresponding to the interlayer exciton.

  3. Transition metal complexes of an isatinic quinolyl hydrazone

    PubMed Central

    2011-01-01

    Background The importance of the isatinic quinolyl hydrazones arises from incorporating the quinoline ring with the indole ring in the same compound. Quinoline ring has therapeutic and biological activities. On the other hand, isatin (1H-indole-2,3-dione) and its derivatives exhibit a wide range of biological activities. Also, the indole ring occurs in Jasmine flowers and Orange blossoms. Recently, the physiological and biological activities of quinolyl hydrazones arise from their tendency to form metal chelates with transition metal ions. In this context, we have reported to isolate, characterize and study the biological activity of some transition metal complexes of an isatinic quinolyl hydrazone; 3-[2-(4-methyl quinolin-2-yl)hydrazono] indolin-2-one. Results Mono- and binuclear as well as dimeric chelates were obtained from the reaction of a new isatinic quinolyl hydrazone with Fe(III), Co(II), Ni(II), Cu(II), VO(II) and Pd(II) ions. The ligand showed a variety of modes of bonding viz. (NNO)2-, (NO)- and (NO) per each metal ion supporting its ambidentate and flexidentate characters. The mode of bonding and basicity of the ligand depend mainly on the type of the metal cation and its counter anion. All the obtained Pd(II)- complexes have the preferable square planar geometry (D4h- symmetry) and depend mainly on the mole ratio (M:L). Conclusion The effect of the type of the metal ion for the same anion (Cl-) is obvious from either structural diversity of the isolated complexes (Oh, Td and D4h) or the various modes of bonding. The isatinic hydrazone uses its lactim form in all complexes (Cl-) except complex 5 (SO42-) in which it uses its lactam form. The obtained Pd(II)- complexes (dimeric, mono- and binuclear) are affected by the mole ratio (M:L) and have the square planar (D4h) geometry. Also, the antimicrobial activity is highly influenced by the nature of the metal ion and the order for S. aureus bacteria is as follows: Nickel(II) > Vanadyl(II) > Cobalt

  4. Selective electrochemical reactivity of rutile VO2 towards the suppression of metal-insulator transition

    NASA Astrophysics Data System (ADS)

    Singh, Sujay; Abtew, Tesfaye A.; Horrocks, Gregory; Kilcoyne, Colin; Marley, Peter M.; Stabile, Adam A.; Banerjee, Sarbajit; Zhang, Peihong; Sambandamurthy, G.

    2016-03-01

    We demonstrate through electrolyte gating measurements of a single nanobeam that the rultile phase of VO2 is electrochemically more reactive than the monoclinic phase. Our results show that the complete suppression of the metal-insulator transition and stabilization of the metallic phase is possible when gate voltage is applied in the rutile metallic phase. The results are discussed based on the formation of oxygen vacancies wherein accommodation of a high concentration of vacancies in the rutile phase selectively stabilizes it by disrupting dimerization of adjacent V-V pairs required for a transition to the monoclinic phase. The creation of oxygen vacancies is proposed to proceed through the oxidation of the electrolyte. Raman spectroscopy data suggest surface metallization upon electrolyte gating with an initial coexistence of insulating monoclinic and metallic domains. The selective electrochemical reactivity of the rutile phase and the resulting defect-induced stabilization of this phase across a vastly expanded temperature window suggest a facile defect engineering route to tune electronic phase transitions.

  5. Dirac cones in transition metal doped boron nitride

    SciTech Connect

    Feng, Min; Cao, Xuewei; Shao, Bin; Zuo, Xu

    2015-05-07

    The transition metal (TM) doped zinc blende boron nitride (c-BN) is studied by using the first principle calculation. TM atoms fill in the interstitials in c-BN and form two-dimensional honeycomb lattice. The generalized gradient approximation and projector augmented wave method are used. The calculated density of states and band structures show that d electrons of TM atoms form impurity bands in the gap of c-BN. When the TM-BN system is in ferromagnetic or non-magnetic state, Dirac cones emerge at the K point in Brillouin zone. When TM is Ti and Co, the Dirac cones are spin polarized and very close to the Fermi level, which makes them promising candidates of Dirac half-metal [H. Ishizuka and Y. Motome, Phys. Rev. Lett. 109, 237207 (2012)]. While TM is Ni and Cu, the system is non-magnetic and Dirac cones located above the Fermi level.

  6. Interaction of hydrogen with transition metal fcc(111) surfaces

    NASA Astrophysics Data System (ADS)

    Löautber, R.; Hennig, D.

    1997-02-01

    The interaction of atomic hydrogen with the fcc(111) surfaces of Pd and Rh was investigated theoretically with an ab initio method, to find out the differences and similiarities between these neighboring metals. At the Rh surface the hcp site of the threefold-coordinated adsorption sites is preferred, while at Pd almost no difference between the hcp and fcc sites was found. For Pd, the occupation of subsurface positions was calculated to be more stable than bulklike positions. The energy gain caused by hydrogen absorption in subsurface positions is only about 100 meV lower than for hydrogen adsorption at the surface. In contrast, for Rh, significant differences between adsorption and absorption were calculated. The diffusion barrier for hydrogen diffusion from surface to subsurface positions was calculated and compared to the diffusion barrier in bulk. The hydrogen-induced work-function changes for the considered 4d transition-metal surfaces were positive for coverage θ=1.

  7. Theoretical study of transition-metal ions bound to benzene

    NASA Technical Reports Server (NTRS)

    Bauschlicher, Charles W., Jr.; Partridge, Harry; Langhoff, Stephen R.

    1992-01-01

    Theoretical binding energies are reported for all first-row and selected second-row transition metal ions (M+) bound to benzene. The calculations employ basis sets of at least double-zeta plus polarization quality and account for electron correlation using the modified coupled-pair functional method. While the bending is predominantly electrostatic, the binding energies are significantly increased by electron correlation, because the donation from the metal d orbitals to the benzene pi* orbitals is not well described at the self-consistent-field level. The uncertainties in the computed binding energies are estimated to be about 5 kcal/mol. Although the calculated and experimental binding energies generally agree to within their combined uncertainties, it is likely that the true binding energies lie in the lower portion of the experimental range. This is supported by the very good agreement between the theoretical and recent experimental binding energies for AgC6H6(+).

  8. Kondo Effects in Single Layer Transition Metal Dichalcogenides

    NASA Astrophysics Data System (ADS)

    Phillips, Michael; Aji, Vivek

    2015-03-01

    Inversion symmetry breaking and strong spin orbit coupling in two dimensional transition metal dichalcogenides leads to interesting new phenomena such as the valley hall and spin hall effects. They display optical circular dichroism and the ability to generate excitation with valley specificity. In this talk we report on the consequences of these properties on correlated states in hole doped systems focussing on the physics of the screening of magnetic impurities. Unlike typical metals, the breaking of inversion symmetry leads to the mixing of a triplet component to the Kondo cloud. Using a variational wave function approach we determine the nature of the many body state. With the ground state in hand we analyze the excitations generated by valley discriminating perturbations. Graduate Student.

  9. Second critical point in first order metal-insulator transitions.

    PubMed

    Kostadinov, Ivan Z; Patton, Bruce R

    2008-11-28

    For first order metal-insulator transitions we show that, together with the dc conductance zero, there is a second critical point where the dielectric constant becomes zero and further turns negative. At this point the metallic reflectivity sharply increases. The two points can be separated by a phase separation state in a 3D disordered system but may tend to merge in 2D. For illustration we evaluate the dielectric function in a simple effective medium approximation and show that at the second point it turns negative. We reproduce the experimental data on a typical Mott insulator such as MnO, demonstrating the presence of the two points clearly. We discuss other experiments for studies of the phase separation state and a similar phase separation in superconductors with insulating inclusions. PMID:19113498

  10. Catalytic graphitization of carbon aerogels by transition metals

    SciTech Connect

    Maldonado-Hodar, F.J.; Moreno-Castilla, C.; Rivera-Utrilla, J.; Hanzawa, Y.; Yamada, Y.

    2000-05-02

    Carbon aerogels and Cr-, Fe-, Co-, and Ni-containing carbon aerogels were obtained by pyrolysis, at temperatures between 500 and 1,800 C, of the corresponding aerogels prepared by the sol-gel method from polymerization of resorcinol with formaldehyde. All samples were characterized by mercury porosimetry, nitrogen adsorption, X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), and Raman spectroscopy. Results obtained show that carbon aerogels are, essentially, macroporous materials that maintain large pore volumes even after pyrolysis at 1,800 C. For pyrolysis at temperatures higher than 1,000 C, the presence of the transition metals produced graphitized areas with three-dimensional stacking order, as shown by HRTEM, XRD, and Raman spectroscopy. HRTEM also showed that the metal-carbon containing aerogels were formed by polyhedral structures. Cr and Fe seem to be the best catalysts for graphitization of carbon aerogels.

  11. Control of plasmonic nanoantennas by reversible metal-insulator transition.

    PubMed

    Abate, Yohannes; Marvel, Robert E; Ziegler, Jed I; Gamage, Sampath; Javani, Mohammad H; Stockman, Mark I; Haglund, Richard F

    2015-01-01

    We demonstrate dynamic reversible switching of VO2 insulator-to-metal transition (IMT) locally on the scale of 15 nm or less and control of nanoantennas, observed for the first time in the near-field. Using polarization-selective near-field imaging techniques, we simultaneously monitor the IMT in VO2 and the change of plasmons on gold infrared nanoantennas. Structured nanodomains of the metallic VO2 locally and reversibly transform infrared plasmonic dipole nanoantennas to monopole nanoantennas. Fundamentally, the IMT in VO2 can be triggered on femtosecond timescale to allow ultrafast nanoscale control of optical phenomena. These unique features open up promising novel applications in active nanophotonics. PMID:26358623

  12. Transition metal catalysis in the mitochondria of living cells.

    PubMed

    Tomás-Gamasa, María; Martínez-Calvo, Miguel; Couceiro, José R; Mascareñas, José L

    2016-01-01

    The development of transition metal catalysts capable of promoting non-natural transformations within living cells can open significant new avenues in chemical and cell biology. Unfortunately, the complexity of the cell makes it extremely difficult to translate standard organometallic chemistry to living environments. Therefore, progress in this field has been very slow, and many challenges, including the possibility of localizing active metal catalysts into specific subcellular sites or organelles, remain to be addressed. Herein, we report a designed ruthenium complex that accumulates preferentially inside the mitochondria of mammalian cells, while keeping its ability to react with exogenous substrates in a bioorthogonal way. Importantly, we show that the subcellular catalytic activity can be used for the confined release of fluorophores, and even allows selective functional alterations in the mitochondria by the localized transformation of inert precursors into uncouplers of the membrane potential. PMID:27600651

  13. Control of plasmonic nanoantennas by reversible metal-insulator transition

    PubMed Central

    Abate, Yohannes; Marvel, Robert E.; Ziegler, Jed I.; Gamage, Sampath; Javani, Mohammad H.; Stockman, Mark I.; Haglund, Richard F.

    2015-01-01

    We demonstrate dynamic reversible switching of VO2 insulator-to-metal transition (IMT) locally on the scale of 15 nm or less and control of nanoantennas, observed for the first time in the near-field. Using polarization-selective near-field imaging techniques, we simultaneously monitor the IMT in VO2 and the change of plasmons on gold infrared nanoantennas. Structured nanodomains of the metallic VO2 locally and reversibly transform infrared plasmonic dipole nanoantennas to monopole nanoantennas. Fundamentally, the IMT in VO2 can be triggered on femtosecond timescale to allow ultrafast nanoscale control of optical phenomena. These unique features open up promising novel applications in active nanophotonics. PMID:26358623

  14. Transition-metal ion impurities in KTaO3

    NASA Astrophysics Data System (ADS)

    Leung, Kevin

    2002-01-01

    A systematic study of transition-metal impurity centers in pervoskites is undertaken by considering isolated Co2+, Fe3+, and Cu2+ point defects in KTaO3. Within the generalized gradient approximation (GGA), the defect center magnetic moments agree with experiments, except for A-site Fe3+ complexes which exhibit 3μB and 5μB structures competitive in energies. It is argued that the anomaly is an artifact of GGA, which underestimates Fe3+ 3d electron correlations. Large (~1 Å) off-center displacements of K-substituting impurities obtain due to metal-oxygen covalent bonding. These A-site dipoles exhibit relaxation dynamics barriers which agree well with experiments. The Fe3+-OI 2- complex is considered in some detail; it exhibits Fe-O bonds considerably shorter than shell-model predictions.

  15. Doping dependent plasmon dispersion in 2 H -transition metal dichalcogenides

    NASA Astrophysics Data System (ADS)

    Müller, Eric; Büchner, Bernd; Habenicht, Carsten; König, Andreas; Knupfer, Martin; Berger, Helmuth; Huotari, Simo

    2016-07-01

    We report the behavior of the charge carrier plasmon of 2 H -transition metal dichalcogenides (TMDs) as a function of intercalation with alkali metals. Intercalation and concurrent doping of the TMD layers have a substantial impact on plasmon energy and dispersion. While the plasmon energy shifts are related to the intercalation level as expected within a simple homogeneous electron gas picture, the plasmon dispersion changes in a peculiar manner independent of the intercalant and the TMD materials. Starting from a negative dispersion, the slope of the plasmon dispersion changes sign and grows monotonously upon doping. Quantitatively, the increase of this slope depends on the orbital character (4 d or 5 d ) of the conduction bands, which indicates a decisive role of band structure effects on the plasmon behavior.

  16. Ising superconductivity and Majorana fermions in transition-metal dichalcogenides

    NASA Astrophysics Data System (ADS)

    Zhou, Benjamin T.; Yuan, Noah F. Q.; Jiang, Hong-Liang; Law, K. T.

    2016-05-01

    In monolayer transition-metal dichalcogenides (TMDs), electrons in opposite K valleys are subject to opposite effective Zeeman fields, which are referred to as Ising spin-orbit coupling (SOC) fields. The Ising SOC, originating from in-plane mirror symmetry breaking, pins the electron spins to the out-of-plane directions, and results in Ising superconducting states with strongly enhanced upper critical fields. Here, we show that the Ising SOC generates equal-spin-triplet Cooper pairs with spin polarized in the in-plane directions. Importantly, the spin-triplet Cooper pairs can induce superconducting pairings in a half-metal wire placed on top of the TMD and result in a topological superconductor with Majorana end states. Direct ways to detect equal-spin triplet Cooper pairs and the differences between Ising superconductors and Rashba superconductors are discussed.

  17. Rare earth-transition metal scrap treatment method

    DOEpatents

    Schmidt, F.A.; Peterson, D.T.; Wheelock, J.T.; Jones, L.L.; Lincoln, L.P.

    1992-02-11

    Rare earth-transition metal (e.g. iron) scrap (e.g. Nd-Fe-B scrap) is melted to reduce the levels of tramp oxygen and nitrogen impurities therein. The tramp impurities are reduced in the melt by virtue of the reaction of the tramp impurities and the rare earth to form dross on the melt. The purified melt is separated from the dross for reuse. The oxygen and nitrogen of the melt are reduced to levels acceptable for reuse of the treated alloy in the manufacture of end-use articles, such as permanent magnets. 3 figs.

  18. Rare earth-transition metal scrap treatment method

    DOEpatents

    Schmidt, Frederick A.; Peterson, David T.; Wheelock, John T.; Jones, Lawrence L.; Lincoln, Lanny P.

    1992-02-11

    Rare earth-transition metal (e.g. iron) scrap (e.g. Nd-Fe-B scrap) is melted to reduce the levels of tramp oxygen and nitrogen impurities therein. The tramp impurities are reduced in the melt by virtue of the reaction of the tramp impurities and the rare earth to form dross on the melt. The purified melt is separated from the dross for reuse. The oxygen and nitrogen of the melt are reduced to levels acceptable for reuse of the treated alloy in the manufacture of end-use articles, such as permanent magnets.

  19. Metal-insulator transition by holographic charge density waves.

    PubMed

    Ling, Yi; Niu, Chao; Wu, Jian-Pin; Xian, Zhuo-Yu; Zhang, Hongbao

    2014-08-29

    We construct a gravity dual for charge density waves (CDWs) in which the translational symmetry along one spatial direction is spontaneously broken. Our linear perturbation calculation on the gravity side produces the frequency dependence of the optical conductivity, which exhibits the two familiar features of CDWs, namely, the pinned collective mode and gapped single-particle excitation. These two features indicate that our gravity dual also provides a new mechanism to implement the metal to insulator phase transition by CDWs, which is further confirmed by the fact that dc conductivity decreases with the decreased temperature below the critical temperature. PMID:25215974

  20. Ionically-mediated electromechanical hysteresis in transition metal oxides

    SciTech Connect

    Kim, Yunseok; Kumar, Amit; Jesse, Stephen; Kalinin, Sergei V

    2012-01-01

    Electromechanical activity, remanent polarization states, and hysteresis loops in paraelectric TiO2 and SrTiO3 are observed. The coupling between the ionic dynamics and incipient ferroelectricity in these materials is analyzed using extended Ginsburg Landau Devonshire (GLD) theory. The possible origins of electromechanical coupling including ionic dynamics, surface-charge induced electrostriction, and ionically-induced ferroelectricity are identified. For the latter, the ionic contribution can change the sign of first order GLD expansion coefficient, rendering material effectively ferroelectric. These studies provide possible explanation for ferroelectric-like behavior in centrosymmetric transition metal oxides.

  1. Theoretical study of electron correlation effects in transition metal dimers

    NASA Astrophysics Data System (ADS)

    Das, Guru P.; Jaffe, Richard L.

    1984-08-01

    Introduction of partially localized orbitals (PLOs) is shown to reduce the number of configurations needed to describe the bonding in transition metal clusters. Using this formalism, estimates are made of the molecular electron correlation energy that arises from including such terms as 3d → 3d', 3p → 3p' and 4s 2 → 4p 2 in the wavefunction. When this estimate of the additional correlation is added to the CAS SCF results of Walch, Bauschlicher, Roos and Nelin improved interaction potentials are obtained for the dimers V 2 and Cr 2.

  2. Ideal tensile strength of B2 transition-metal aluminides

    NASA Astrophysics Data System (ADS)

    Li, Tianshu; Morris, J. W., Jr.; Chrzan, D. C.

    2004-08-01

    The ideal tensile strengths of the B2 -type (CsCl) transition-metal aluminides FeAl , CoAl , and NiAl have been investigated using an ab initio electronic structure total energy method. The three materials exhibit dissimilar mechanical behaviors under the simulated ideal tensile tests along [001], [110], and [111] directions. FeAl is weakest in tension along [001] whereas CoAl and NiAl are strongest in the same direction. The weakness of FeAl along [001] direction is attributed to the instability introduced by the filling of antibonding d states.

  3. Negative ion photoelectron spectroscopy of bare transition metal dimers

    NASA Astrophysics Data System (ADS)

    Barker, Beau J.

    This thesis contains gas phase negative ion photoelectron spectra of Mo2, MoV, CrCu, MoCu and Cu2. Spectra were taken with 488 nm and 514 nm light at a resolution of 4-5 meV. Information such as electron affinities, vibrational frequencies, anharmonicities and bond dissociation energies are reported for the ground and excited electronic states of both the anion and neutral species. Theoretical calculations at the density functional level are also reported for these species. Experiment and theory are used to analyze the bonding in these bare transition metal dimers.

  4. A simple, general route to 2-pyridylidene transition metal complexes.

    PubMed

    Roselló-Merino, Marta; Díez, Josefina; Conejero, Salvador

    2010-12-28

    Pyridinium 2-carboxylates decompose thermally in the presence of a variety of late transition metal precursors to yield the corresponding 2-pyridylidene-like complexes. The mild reaction conditions and structural diversity that can be generated in the heterocyclic ring make this method an attractive alternative for the synthesis of 2-pyridylidene complexes. IR spectra of the Ir(i) carbonyl compounds [IrCl(NHC)(CO)(2)] indicate that these N-heterocyclic carbene ligands are among the strongest σ-electron donors. PMID:21052586

  5. Functionalization of Two-Dimensional Transition-Metal Dichalcogenides.

    PubMed

    Chen, Xin; McDonald, Aidan R

    2016-07-01

    Two-dimensional (2D) layered transition-metal dichalcogenides (TMDs) are a fascinating class of nanomaterials that have the potential for application in catalysis, electronics, photonics, energy storage, and sensing. TMDs are rather inert, and thus pose problems for chemical derivatization. However, to further modify the properties of TMDs and fully harness their capabilities, routes towards their chemical functionalization must be identified. Herein, recent efforts toward the chemical (bond-forming) functionalization of 2D TMDs are critically reviewed. Recent successes are highlighted, along with areas where further detailed analyses and experimentation are required. This burgeoning field is very much in its infancy but has already provided several important breakthroughs. PMID:26848815

  6. Band engineering in transition metal dichalcogenides: Stacked versus lateral heterostructures

    NASA Astrophysics Data System (ADS)

    Guo, Yuzheng; Robertson, John

    2016-06-01

    We calculate a large difference in the band alignments for transition metal dichalcogenide (TMD) heterojunctions when arranged in the stacked layer or lateral (in-plane) geometries, using direct supercell calculations. The stacked case follows the unpinned limit of the electron affinity rule, whereas the lateral geometry follows the strongly pinned limit of alignment of charge neutrality levels. TMDs therefore provide one of the few clear tests of band alignment models, whereas three-dimensional semiconductors give less stringent tests because of accidental chemical trends in their properties.

  7. Structural and Electrochemical Characterization of Lithium Transition Metal Phosphates

    NASA Astrophysics Data System (ADS)

    Hashambhoy, Ayesha Maria

    The lithium ion battery has emerged as one of the most promising hybrid vehicle energy storage systems of the future. Of the potential cathode chemistries explored, lithium transition metal phosphates have generated a significant amount of interest due to their low-cost precursors, potential ease of synthesis, stability, and their environmentally friendly nature. This is in contrast to layered oxide systems such as LiCoO2, which have long been considered state of the art, but are now being reevaluated due to their structural instability at elevated temperatures, and higher cost. In particular, LiFePO4 has an operating potential comparable to those batteries available on the market (˜3.5V vs. Li/Li+), and higher theoretical specific capacity (170mAh/g vs. that of LiCoO2 which is 140mAh/g). The manganese analog to LiFePO4, LiMnPO4, exhibits a higher operating potential (˜4.1V v Li/Li+), and the same theoretical capacity, however Li-ion diffusion through this structure is much more rate limited and its theoretical capacity cannot be realized at rates suitable for commercial applications. The purpose of this work was threefold: 1) To explore the impact of Fe substitution on Mn sites in LiMnPO 4. 2) To examine the effects of alterations to the particle/electrolyte interface on rate capability. 3) To explore a novel fabrication route for LiMnPO4 using microwaves, and determine an optimal power and time combination for best performance. The coexistence of Fe and Mn on the transition metal site M, of LiMPO 4 resulted in an improved apparent Li-ion diffusivity in both Fe and Mn regimes as compared to that observed for LiFePO4 and LiMnPO 4 respectively. Calculations made from two different analysis methods, cyclic voltammetry (CV) and galvanostatic intermittent titration (GITT) drew this same conclusion. The signature characteristics observed from the CVs pertaining to single and dual phase reactions led to a delithiation model of LiFe0.5Mn0.5PO4 proposing the localization

  8. He-He and He-metal interactions in transition metals from first-principles

    NASA Astrophysics Data System (ADS)

    Zhang, Pengbo; Zou, Tingting; Zhao, Jijun

    2015-12-01

    We investigated the atomistic mechanism of He-He and He-metal interactions in bcc transition metals (V, Nb, Ta, Cr, Mo, W, and Fe) using first-principles methods. We calculated formation energy and binding energy of He-He pair as function of distance within the host lattices. The strengths of He-He attraction in Cr, Mo, W, and Fe (0.37-1.11 eV) are significantly stronger than those in V, Nb, and Ta (0.06-0.17 eV). Such strong attractions mean that He atoms would spontaneously aggregate inside perfect Cr, Mo, W, and Fe host lattices in absence of defects like vacancies. The most stable configuration of He-He pair is <100> dumbbell in groups VB metals, whereas it adopts close <110> configuration in Cr, Mo, and Fe, and close <111> configuration in W. Overall speaking, the He-He equilibrium distances of 1.51-1.55 Å in the group VIB metals are shorter than 1.65-1.70 Å in the group VB metals. Moreover, the presence of interstitial He significantly facilitates vacancy formation and this effect is more pronounced in the group VIB metals. The present calculations help understand the He-metal/He-He interaction mechanism and make a prediction that He is easier to form He cluster and bubbles in the groups VIB metals and Fe.

  9. Brittle-to-Ductile Transition in Metallic Glass Nanowires.

    PubMed

    Şopu, D; Foroughi, A; Stoica, M; Eckert, J

    2016-07-13

    When reducing the size of metallic glass samples down to the nanoscale regime, experimental studies on the plasticity under uniaxial tension show a wide range of failure modes ranging from brittle to ductile ones. Simulations on the deformation behavior of nanoscaled metallic glasses report an unusual extended strain softening and are not able to reproduce the brittle-like fracture deformation as found in experiments. Using large-scale molecular dynamics simulations we provide an atomistic understanding of the deformation mechanisms of metallic glass nanowires and differentiate the extrinsic size effects and aspect ratio contribution to plasticity. A model for predicting the critical nanowire aspect ratio for the ductile-to-brittle transition is developed. Furthermore, the structure of brittle nanowires can be tuned to a softer phase characterized by a defective short-range order and an excess free volume upon systematic structural rejuvenation, leading to enhanced tensile ductility. The presented results shed light on the fundamental deformation mechanisms of nanoscaled metallic glasses and demarcate ductile and catastrophic failure. PMID:27248329

  10. Origin of Transitions between Metallic and Insulating States in Simple Metals

    NASA Astrophysics Data System (ADS)

    Naumov, Ivan I.; Hemley, Russell J.

    2015-04-01

    Unifying principles that underlie recently discovered transitions between metallic and insulating states in elemental solids under pressure are developed. Using group theory arguments and first-principles calculations, we show that the electronic properties of the phases involved in these transitions are controlled by symmetry principles. The valence bands in these systems are described by simple and composite band representations constructed from localized Wannier functions centered on points unoccupied by atoms, and which are not necessarily all symmetrical. The character of the Wannier functions is closely related to the degree of s -p (-d ) hybridization and reflects multicenter chemical bonding in these insulating states. The conditions under which an insulating state is allowed for structures having an integer number of atoms per primitive unit cell as well as reentrant (i.e., metal-insulator-metal) transition sequences are detailed, resulting in predictions of behavior such as phases having band-contact lines. The general principles developed are tested and applied to the alkali and alkaline earth metals, including elements where high-pressure insulating phases have been reported (e.g., Li, Na, and Ca).

  11. Nucleation and growth of noble metals on transition-metal di-tellurides

    NASA Astrophysics Data System (ADS)

    Hla, S. W.; Marinković, V.; Prodan, A.

    1997-04-01

    Transition-metal di-tellurides (α- and β-MoTe 2 and WTe 2) were used as substrates for nucleation and growth studies of noble metals. They represent a group of chemically closely related compounds with different surface topographies. Nucleation and growth of Ag and Au at room temperature were studied by means of UHV-STM, AFM and TEM. The results revealed that the growth and orientation of these metals are influenced by the topography of the substrate surfaces. Contrary to the growth on atomically flat α-MoTe 2, there is an enhanced diffusion and nucleation along the periodic surface troughs on β-MoTe 2 and WTe 2. The topography of their (001) surfaces is responsible for the orientation of metal (112) planes being parallel to the substrate surface.)

  12. Photo- and electrocatalytic H2 production by new first-row transition-metal complexes based on an aminopyridine pentadentate ligand.

    PubMed

    Call, Arnau; Codolà, Zoel; Acuña-Parés, Ferran; Lloret-Fillol, Julio

    2014-05-12

    The synthesis and characterisation of the pentadentate ligand 1,4-di(picolyl)-7-(p-toluenesulfonyl)-1,4,7-triazacyclononane (Py2(Ts)tacn) and their metal complexes of general formula [M(CF3SO3)(Py2(Ts)tacn)][CF3SO3], (M = Fe (1Fe), Co (1Co) and Ni (1Ni)) are reported. Complex 1Co presents excellent H2 photoproduction catalytic activity when using [Ir(ppy)2(bpy)]PF6 (PSIr) as photosensitiser (PS) and Et3N as electron donor, but 1Ni and 1Fe result in a low activity and a complete lack of it, respectively. On the other hand, all three complexes have excellent electrocatalytic proton reduction activity in acetonitrile, when using trifluoroacetic acid (TFA) as a proton source with moderate overpotentials for 1Co (0.59 V vs. SCE) and 1Ni (0.56 V vs. SCE) and higher for 1Fe (0.87 V vs. SCE). Under conditions of CH3CN/H2O/Et3N (3:7:0.2), 1Co (5 μM), with PSIr (100 μM) and irradiating at 447 nm gives a turnover number (TON) of 690 (n H2/n1Co) and initial turnover frequency (TOF) (TON×t(-1)) of 703 h(-1) for H2 production. It should be noted that 1Co retains 25 % of the catalytic activity for photoproduction of H2 in the presence of O2. The inexistence of a lag time for H2 evolution and the absence of nanoparticles during the first 30 min of the reaction suggest that the main catalytic activity observed is derived from a molecular system. Kinetic studies show that the reaction is -0.7 order in catalyst, and time-dependent diffraction light scattering (DLS) experiments indicate formation of metal aggregates and then nanoparticles, leading to catalyst deactivation. By a combination of experimental and computational studies we found that the lack of activity in photochemical water reduction by 1Fe can be attributed to the 1Fe (II/I) redox couple, which is significantly lower than the PSIr (III/II) , while for 1Ni the pKa value (-0.4) is too small in comparison with the pH (11.9) imposed by the use of Et3N as electron donor. PMID:24692261

  13. Transition radiation in metal-metal multilayer nanostructures as a medical source of hard x-ray radiation

    SciTech Connect

    Pokrovsky, A. L.; Kaplan, A. E.; Shkolnikov, P. L.

    2006-08-15

    We show that a periodic metal-metal multilayer nanostructure can serve as an efficient source of hard x-ray transition radiation. Our research effort is aimed at developing an x-ray source for medical applications, which is based on using low-energy relativistic electrons. The approach toward choosing radiator-spacer couples for the generation of hard x-ray resonant transition radiation by few-MeV electrons traversing solid multilayer structures for the energies of interest to medicine (30-50 keV) changes dramatically compared with that for soft x-ray radiation. We show that one of the main factors in achieving the required resonant line is the absence of the contrast of the refractive indices between the spacer and the radiator at the far wings of the radiation line; for that purpose, the optimal spacer, as a rule, should have a higher atomic number than the radiator. Having experimental goals in mind, we have considered also the unwanted effects due to bremsstrahlung radiation, absorption and scattering of radiated photons, detector-related issues, and inhibited coherence of transition radiation due to random deviation of spacing between the layers. Choosing as a model example a Mo-Ag radiator-spacer pair of materials, we demonstrate that the x-ray transition radiation line can be well resolved with the use of spatial and frequency filtering.

  14. Ultrafast exciton relaxation in monolayer transition metal dichalcogenides

    NASA Astrophysics Data System (ADS)

    Thilagam, A.

    2016-04-01

    We examine a mechanism by which excitons undergo ultrafast relaxation in common monolayer transition metal dichalcogenides. It is shown that at densities ≈1 × 1011 cm-2 and temperatures ≤60 K, excitons in well known monolayers (MoS2, MoSe2, WS2, and WSe2) exist as point-like structureless electron-hole quasi-particles. We evaluate the average rate of exciton energy relaxation due to acoustic phonons via the deformation potential and the piezoelectric coupling mechanisms and examine the effect of spreading of the excitonic wavefunction into the region perpendicular to the monolayer plane. Our results show that the exciton relaxation rate is enhanced with increase in the exciton temperature, while it is decreased with increase in the lattice temperature. Good agreements with available experimental data are obtained when the calculations are extrapolated to room temperatures. A unified approach taking into account the deformation potential and piezoelectric coupling mechanisms shows that exciton relaxation induced by phonons is as significant as defect assisted scattering and trapping of excitons by surface states in monolayer transition metal dichalcogenides.

  15. Stabilization of Small Boron Cage by Transition Metal Encapsulation

    NASA Astrophysics Data System (ADS)

    Zhang, Lijun; Lv, Jian; Wang, Yanchao; Ma, Yanming

    2015-03-01

    The discovery of chemically stable fullerene-like structures formed by elements other than carbon has been long-standing desired. On this aspect significant efforts have centered around boron, only one electron deficient compared with carbon. However, during the past decade a large number of experimental and theoretical studies have established that small boron clusters are either planar/quasi-planar or forming double-ring tubular structures. Until recently, two all-boron fullerenes have been independently discovered: B38 proposed by our structure searching calculations and B40 observed in a joint experimental and theoretical study. Here we extend our work to the even smaller boron clusters and propose an effective routine to stabilize them by transition metal encapsulation. By combining swarm-intelligence structure searching and first-principles calculations, we have systematically investigated the energy landscapes of transition-metal-doped MB24 clusters (M = Ti, Zr, Hf, Cr, Mo, W, Fe, Ru and Os). Two stable symmetric endohedral boron cages, MoB24 and WB24 are identified. The stability of them can be rationalized in terms of their unique 18-electron closed-shell electronic structures. Funded by Recruitment Program of Global Experts of China and China Postdoctoral Science Foundation.

  16. Anderson metal-insulator transitions with classical magnetic impurities

    NASA Astrophysics Data System (ADS)

    Jung, Daniel; Kettemann, Stefan; Slevin, Keith

    2016-04-01

    We study numerically the effects of classical magnetic impurities on the Anderson metal-insulator transition. We find that a small concentration of Heisenberg impurities enhances the critical disorder amplitude Wc with increasing exchange coupling strength J . The resulting scaling with J is analyzed which supports an anomalous scaling prediction by Wegner due to the combined breaking of time-reversal and spin-rotational symmetry. Moreover, we find that the presence of magnetic impurities lowers the critical correlation length exponent ν and enhances the multifractality parameter α0. The new value of ν improves the agreement with the value measured in experiments on the metal-insulator transition (MIT) in doped semiconductors like phosphor-doped silicon, where a finite density of magnetic moments is known to exist in the vicinity of the MIT. The results are obtained by a finite-size scaling analysis of the geometric mean of the local density of states which is calculated by means of the kernel polynomial method. We establish this combination of numerical techniques as a method to obtain critical properties of disordered systems quantitatively.

  17. Properties of binary transition-metal arsenides (TAs)

    NASA Astrophysics Data System (ADS)

    Saparov, Bayrammurad; Mitchell, Jonathan E.; Sefat, Athena S.

    2012-08-01

    We present thermodynamic and transport properties of transition-metal (T) arsenides, TAs, with T = Sc to Ni (3d), Zr, Nb, Ru (4d), Hf and Ta (5d). Characterization of these binaries is carried out with powder x-ray diffraction, temperature- and field-dependent magnetization and resistivity, temperature-dependent heat capacity, Seebeck coefficient, and thermal conductivity. All binaries show metallic behavior except TaAs and RuAs. TaAs, NbAs, ScAs and ZrAs are diamagnetic, while CoAs, VAs, TiAs, NiAs and RuAs show approximately Pauli paramagnetic behavior. FeAs and CrAs undergo antiferromagnetic ordering below TN ≈ 71 K and TN ≈ 260 K, respectively. MnAs is a ferromagnet below TC ≈ 317 K and undergoes hexagonal-orthorhombic-hexagonal transitions at TS ≈ 317 K and 384 K, respectively. For TAs, Seebeck coefficients vary between + 40 and - 40 μV K-1 in the 2-300 K range, whereas thermal conductivity values stay below 18 W m-1 K-1. The Sommerfeld coefficients γ are less than 10 mJ K-2 mol-1. At room temperature with application of 8 T magnetic field, large positive magnetoresistance is found for TaAs (˜25%), MnAs (˜90%) and NbAs (˜75%).

  18. Transition metal oxide as anode interface buffer for impedance spectroscopy

    NASA Astrophysics Data System (ADS)

    Xu, Hui; Tang, Chao; Wang, Xu-Liang; Zhai, Wen-Juan; Liu, Rui-Lan; Rong, Zhou; Pang, Zong-Qiang; Jiang, Bing; Fan, Qu-Li; Huang, Wei

    2015-12-01

    Impedance spectroscopy is a strong method in electric measurement, which also shows powerful function in research of carrier dynamics in organic semiconductors when suitable mathematical physical models are used. Apart from this, another requirement is that the contact interface between the electrode and materials should at least be quasi-ohmic contact. So in this report, three different transitional metal oxides, V2O5, MoO3 and WO3 were used as hole injection buffer for interface of ITO/NPB. Through the impedance spectroscopy and PSO algorithm, the carrier mobilities and I-V characteristics of the NPB in different devices were measured. Then the data curves were compared with the single layer device without the interface layer in order to investigate the influence of transitional metal oxides on the carrier mobility. The careful research showed that when the work function (WF) of the buffer material was just between the work function of anode and the HOMO of the organic material, such interface material could work as a good bridge for carrier injection. Under such condition, the carrier mobility measured through impedance spectroscopy should be close to the intrinsic value. Considering that the HOMO (or LUMO) of most organic semiconductors did not match with the work function of the electrode, this report also provides a method for wide application of impedance spectroscopy to the research of carrier dynamics.

  19. Electron-phonon coupling and structural phase transitions in early transition metal oxides and chalcogenides

    NASA Astrophysics Data System (ADS)

    Farley, Katie Elizabeth

    Pronounced nonlinear variation of electrical transport characteristics as a function of applied voltage, temperature, magnetic field, strain, or photo-excitation is usually underpinned by electronic instabilities that originate from the complex interplay of spin, orbital, and lattice degrees of freedom. This dissertation focuses on two canonical materials that show pronounced discontinuities in their temperature-dependent resistivity as a result of electron---phonon and electron---electron correlations: orthorhombic TaS3 and monoclinic VO2. Strong electron-phonon interactions in transition metal oxides and chalcogenides results in interesting structural and electronic phase transitions. The properties of the material can be changed drastically in response to external stimuli such as temperature, voltage, or light. Understanding the influence these interactions have on the electronic structure and ultimately transport characteristics is of utmost importance in order to take these materials from a fundamental aspect to prospective applications such as low-energy interconnects, steep-slope transistors, and synaptic neural networks. This dissertation describes synthetic routes to nanoscale TaS3 and VO2, develops mechanistic understanding of their electronic instabilities, and in the case of the latter system explores modulation of the electronic and structural phase transition via the incorporation of substitutional dopant atoms. We start in chapter 2 with a detailed study of the synthesis and electronic transport properties of TaS3, which undergoes a Peierls' distortion to form a charge density wave. Scaling this material down to the nanometer-sized regime allows for interrogation of single or discrete phase coherent domains. Using electrical transport and broad band noise measurements, the dynamics of pinning/depinning of the charge density wave is investigated. Chapter 3 provides a novel synthetic approach to produce high-edge-density MoS2 nanorods. MoS2 is a

  20. Synthesis of transition metal arsenides and arsenic metal sulfides and their role in the dearsenation of shale oils

    SciTech Connect

    Singhal, G.H.; Brown, L.D.; Ryan, D.F. )

    1994-04-01

    One of the chief problems in upgrading shale oil is the presence of inherent arsenic, which is known to poison downstream catalysts. Highly dispersed transition metal sulfides formed in situ from the decomposition of dithiocarbamate (DTC) complexes of transition metals show excellent potential as dearsenation agents. The authors have studied the reaction of these sulfides with various arsenic compositions, and characterized the metal arsenides and arsenic metal sulfides formed as well as the ease of their formation. Thus, the reaction of bis(butyldithiocarbamato)Ni, (NiBuDTC), with model compounds was very facile and gave NiAs, NiAsS, and NiAs[sub 2[minus]x]S[sub x]. In general, the effectiveness of the sulfides for dearsenation followed the sequence Ni > Mo [much gt] Co, while iron sulfides were totally ineffective. Based upon these results, tests where run in autoclaves (as well as a fixed-bed flow-through unit) with Ni BuDTC and shale oil having 73 ppm inherent As. Under optimum conditions, dearsenation down to less than 1 ppm was obtained.