155,224 research outputs found
Electrical, morphological and structural properties of RF magnetron sputtered Mo thin films for application in thin film photovoltaic solar cells
No full textMolybdenum (Mo) thin films were deposited using radio frequency magnetron sputtering, for application as a metal back contact material in ‘‘substrate configuration’’ thin film solar cells. The variations of the electrical, morphological, and structural properties of the deposited films with sputtering pressure, sputtering power and post-deposition annealing were determined. The electrical conductivity of the Mo films was found to increase with decreasing sputtering pressure and increasing sputtering power. X-ray diffraction data showed that all the films had a (110) preferred orientation that became less pronounced at higher sputtering power while being relatively insensitive to process pressure. The lattice stress within the films changed from tensile to compressive with increasing sputtering power and the tensile stress increased with increasing sputtering pressure. The surface morphology of the films changed from pyramids to cigar-shaped grains for a sputtering power between 100 and 200 W, remaining largely unchanged at higher power. These grains were also observed to decrease in size with increasing sputtering pressure. Annealing the films was found to affect the resistivity and stress of the films. The resistivity increased due to the presence of residual oxygen and the stress changed from tensile to compressive. The annealing step was not found to affect the crystallisation and grain growth of the Mo films
Unusually heavy stable Mo isotope signatures of the Ottawa River: Causes and implications for global riverine Mo fluxes
No full textThe accurate use of Mo isotope mass balance modelling of ancient oceans relies on the assumption that the δ98Mo of modern riverine inputs represents a reasonable estimate of the past. A growing number of studies of global rivers have demonstrated significant variation in δ98Mo from the bedrock sources of Mo. The Ottawa River, Canada, was previously identified as having an anomalously heavy Mo isotope composition, with a δ98Mo signature close to seawater (2.3‰), for a seemingly pristine natural river. To further explore this unusual signature, we collected and filtered 29 water samples from the Ottawa River, tributaries, and small lakes, and analysed them for Mo isotopes as well as major and trace elements. Here, we fully document heavy δ98Mo signatures throughout the Ottawa River and its absence in surrounding areas of the wider Ottawa River basin (ORB). Our results reveal a progressive upstream increase in both Mo concentration and δ98Mo signatures in the Ottawa River towards values even heavier than seawater, up to 3.13‰ – the heaviest Mo isotopic signature of river water measured to date. In contrast, the tributaries and lakes display far lighter and more consistent δ98Mo signatures within the range previously found in other rivers. Weathering of an isotopically heavy bedrock source, fractionation during weathering and retention of light isotopes in soils have all been proposed as sources of heavy δ98Mo in rivers; however, none of these mechanisms can satisfactorily explain our new observations. Colloidal and particulate processes that remove elements downstream, as inferred from some trace element proxies, also cannot explain the decreasing δ98Mo, since the preferential removal of light Mo isotopes is predicted from these processes. Similarly, the downstream trends show no apparent relationships with constructed dams or known potential industrial sources. Therefore, our findings from the Ottawa River are best explained as the dilution of a yet unidentified point source of heavy Mo upstream of sampling, or a significant permanent sink for light isotopes existing only in the upper reaches of the catchment. In both cases, anthropogenic contribution from a large mining district in the headwaters of the river must be considered and should be explored further. Fractionation of Mo in waste rock storage facilities have been previously identified and may provide an unnatural sink for isotopically light Mo through the Rayleigh-type fractionation of dissolved Mo on oxyhydr(oxide) mineral surfaces. The implied anthropogenic alteration of the natural Mo cycle highlights the significant and wide-reaching effects of unnatural point sources of Mo on the cumulative δ98Mo signatures of the catchment, and emphasises the necessity for detailed geochemical screening of anomalous river water isotope signatures before natural isotope compositions are inferred
Studies on Bis(imido) molybdenum complexes containing unsaturated hydrocarbon ligands
No full textThis thesis describes the synthesis and characterisation of molybdenum bis(imido) complexes containing unsaturated hydrocarbon ligands. A principal objective of the work was to examine the effect of various imido substituents on the coordination number of the complex and the orientations adopted by olefin and acetylene ligands. Chapter One highlights areas of transition metal chemistry relevant to the thesis, with particular emphasis on the psuedo-isolobal analogy between cyclopentadienyl and imido ligands, A convenient one-pot synthesis of molybdenum bis(imido) complexes of the type Mo(NR)(NR')Cl(_2).DME (R=R'=l-adamantyl, 2-t- BUC(_6)H(_4); R=2,6-i-Pr(_2)C(_6)H(_3), R'=t-Bu) is described in Chapter Two. Mo(N-l- adamantyl)(O)Cl(_2).DME has been synthesised, and its structure determined by single crystal X-ray diffraction.- The preparation of olefin complexes Mo(NR)(NR')(C(_2)H(_4))(PMe(_3))n (R=R'=l-adamantyl, n=l; R=R'=2-t-BuC(_6)H(_4), n=2; R=2,6-i-Pr(_2)C(_6)H(_3), R'=t- Bu, n=l) is outlined in Chapter Three. Structural information derived from NMR data has allowed comparison with metallocene-like olefin adducts. Chapter Four describes the synthesis of complexes containing σ-bound phenyl ligands (Mo(NR)(NR')(σ-C(_6)H(_5))(PMe(_3)) (R=R'=l-adamantyl, 2-t-BuC(_6)H(_4); R=2,6-i-Pr(_2)C(_6)H(_3), R'=t-Bu)) as potential precursors to benzyne complexes. Chapter Five describes the preparation of diphenylacetylene complexes Mo(NR)(NR')(PhC=CPh)(PMe(_3)), structural information derived from NMR data allows comparison with previously known metallocene-like acetylene complexes. Full experimental details for Chapters Two to Five are given in Chapter Six
A Cartouche, Louisiana Purchase Exposition, St. Louis, Mo.
No full textSection of Cartouche carved by P. Wiehle (who also sculpted for the 1893 Columbia Exposition Administration Buildin)g ; stamped "G.W. Byrd
A NEGATIVE ION PHOTOELECTRON SPECTROSCOPIC AND COMPUTATIONAL STUDY OF Mo AND Mo
No full textAuthor Institution: Department of Chemistry, University of Minnesota, Minneapolis, MN 55455We report the 488 and 514 nm anion photoelectron spectra of Mo. Neutral Mo has been described in recent studies as having a bond order of six, predicted to be the highest of any homonuclear diatomic, exceeding even that of Cr(five). The photoelectron spectrum of Moconfirms the previously measured vibrational frequency of gas phase Mo and displays transitions to vibrational levels up to v=7 in its ground state. The electron affinity of Mo is measured to be 0.732 0.010 eV. The Mo ground state is assigned as a state, in which the extra electron occupies a formally antibonding orbital of primarily 5 atomic parentage. A Franck-Condon analysis of the vibrational band intensities indicates a change in the equilibrium bond length of only 0.03 0.02 \AA upon electron detachment. These results, and the similar vibrational frequencies measured for Mo and Mo, suggest that the anion HOMO is essentially nonbonding. Weak photodetachment transitions to excited states of Mo lying within 1.2 eV of its ground state are also observed. DFT calculations using the BPW91/SDD method show good agreement with experiment for the electron affinity of Mo and the bond lengths in the anion and neutral molecule ground states. It is hoped that these spectroscopic results will motivate and assist high level theoretical studies of the Mo anion
Different species of FFA concentrations (nmol/g) of 6 mo and 12 mo NEXLPL+/- mice in hippocampus.
No full text<p>m/z: molecular weight of FFA. 6 mo: CTR n = 4, NEXLPL+/- n = 6; 12 mo: CTR n = 3, NEXLPL+/- n = 6.</p><p>Different species of FFA concentrations (nmol/g) of 6 mo and 12 mo NEXLPL+/- mice in hippocampus.</p
Comparative calculation of EPR spectral parameters in [Mo^VOX_4]^-, [Mo^VOX_5]^(2-), and [Mo^VOX_4(H_2O)]^- complexes
No full textThe EPR spectral parameters, i.e. g-tensors and molybdenum hyperfine couplings, for several d^1 systems of the general formula [Mo^VEX_4]^(n-), [Mo^VOX_5]^(2-), and [Mo^VOX_4(H_2O)]^- (E = O, N; X = F, Cl, Br; n = 1 or 2) were calculated using Density Functional Theory. The influence of basis sets, their contraction scheme, the type of exchange-correlation functional, the amount of Hartree-Fock exchange, molecular geometry, and relativistic effects on the calculated EPR spectra parameters have been discussed. The g-tensors and molybdenum hyperfine coupling parameters were calculated using a relativistic Hamiltonian coupled with several LDA, GGA, and 'hybrid' exchange-correlation functionals and uncontracted full-electron DGauss DZVP basis sets. The calculated EPR parameters are found to be sensitive to the Mo=E distance and E=Mo-Cl angle, and thus the choice of starting molecular geometry should be considered as an important factor in predicting the g-tensors and hyperfine coupling constants in oxo-molybdenum compounds. In the present case, the GGA exchange-correlation functionals provide a better agreement between the theory and the experiment
Preparation and microstructural characterization of nanosized Mo-TiO2 and Mo-W-O thin films by sputtering: tailoring of composition and porosity by thermal treatment
No full textNanosized Mo doped TiO2 and mixed W–Mo oxide thin films were deposited via RF-magnetron sputtering, in either reactive or inert atmosphere, to study the influence of the plasma gas on the film growth. Mixed targets (Ti (97 at.%)–Mo (3 at.%) and W (12 at.%)–Mo (88 at.%)) were used for the purpose. Thermal treatments were performed to promote structural and chemical changes. Experimental evidences highlighted the dependence of structural, morphological and compositional evolution of the films on the annealing temperature. In particular, coalescence inhibition to titania nanograins induced by Mo was observed in the Mo doped TiO2 films. The different volatility of WO3 and MoO3 in the W–Mo mixed oxides greatly affected the evolution of the film through annealing. This method proved useful to tailor the composition and porosity of the layers. Mo doped TiO2 films were tested as chemoresistive sensors towards ethanol; mixed W–Mo oxide were found to respond to CO
Hon. Benj. G. Brown, MO.
No full textTitle from unverified information on negative sleeve.Hon. Benj. Gray Brown; Sen. from MO.; B. 1826- Ky; D. 1885-Mo.; Graduate from Yale 1847; member State H of R- 52-58; Editor of Mo. Democrat 54-59; Commanded regiment in the Union Army; U.S. Senate 1862-67; Gov. of Mo. 1871; Nominated for V. Pres 1872 on Greeley Ticket.Forms part of Brady-Handy Photograph Collection (Library of Congress)
- …
