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Garrett, Benjamin RMoO(S2)2L Based Molecular Electrocatalysts for Hydrogen Production
Doctor of Philosophy, The Ohio State University, 2017, Chemistry
Electrochemical and photoelectrochemical water splitting are promising ways to store energy from intermittent sources (i.e. wind and solar), in the form of hydrogen. Water splitting can be divided into two half reactions: the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER), both of which need catalysts to reduce the overpotential, thereby increasing energy efficiencies. The best HER electrocatalyst to date is well-known to be platinum (Pt), which has a near-zero overpotential. Crystalline and amorphous molybdenum sulfide (Mo—S) catalysts are leaders as earth abundant materials for electrocatalytic hydrogen production. The development of a molecular motif inspired by the Mo—S catalytic materials and their active sites is of interest, as molecular species possess a great degree of tunable electronic properties. Modular synthetic routes were developed to produce five molecular complexes centered around the MoO(S2)2L structural motif. The MoO(S2)2L complexes were tested as electrocatalysts for the HER in aqueous and non-aqueous conditions and HER performances were affected by composition of L. The overpotentials and TOF of the MoO(S2)2L complexes studied reveal these complexes as promising homogeneous electrocatalysts for hydrogen production. Finally, reductive pathways of MoO(S2)2bpy (Mo-bpy) (bpy = 2,2’-bipyridine) were explored from both experimental and theoretical studies. We monitored chemical reduction of Mo-bpy with UV-Vis spectroscopy and found that Mo-bpy undergoes anionic persulfide reduction to form the tetragonal Mo(VI) complex [MoOS3]2-. Theoretical catalytic reaction pathways were explored, revealing that Mo=O may function as a proton relay. With the synthetic and theoretical insight gained, we then set out to hetereogenize the MoO(S2)2L structural motif into a polymeric backbone, MoS-P4VP. We compared catalytic performance metrics of MoS-P4VP to MoO(S¬2)2(4,4’-di-tert-butyl-2,2’-bipyridine (Mo-tbpy). The marked increase in catalytic performance for MoS-P4VP relative to Mo-tbpy lead us to explore the catalytic polymer structure in detail and propose the structure of MoS-P4VP to consist of Mo(V) centers along with bridging sulfides, [Mo2O2S8]2-, not the expected MoS-P4VP framework (Mo-dimer). Recent reports reveal the importance of the Mo=O moiety in a-MoSx. We present evidence that Mo-dimer, without the P4VP framework performs well as a catalyst. Therefore, we propose the Mo-dimer may be a good molecular mimic of a-MoSx. The MoO(S2)2L structural motif and the mechanistic work presented herein is of broad interest for amorphous Mo-S (a-MoSx) electrocatalytic materials and anion-redox chalcogel battery materials.

Committee:

Yiying Wu (Advisor); Christopher Hadad (Advisor); James Cowan (Committee Member); Karl Danneberger (Committee Member)

Subjects:

Chemistry

Keywords:

Molybdenum, hydrogen, electrocatalysis, proton reduction, Inorganic, Synthesis

Lee, Bom SoonGaseous sulfidation of pure molybdenum at 700̊ - 950̊C /
Doctor of Philosophy, The Ohio State University, 1980, Graduate School

Committee:

Not Provided (Other)

Subjects:

Engineering

Keywords:

Molybdenum

Hagerty, PhillipPhysical Vapor Deposition of Materials for Flexible Two Dimensional Electronic Devices
Master of Science (M.S.), University of Dayton, 2016, Chemical Engineering
Molybdenum Disulfide (MoS2) and Tungsten Disulfide (WS2) are two materials in a larger class of materials known as Transition Metal Dichalcogenides (TMDs) that have begun emerge as semiconducting materials. When their horizontal length scale is reduced from bulk to monolayer they demonstrate surprising combinations of properties including a direct electronic band gap and mechanical flexibility. Two dimensional (2D) materials have the potential to revolutionize performance and tailorability of electro-optical devices fabricated entirely from molecularly thin materials. In a departure from traditional exfoliation or high temperature chemical vapor deposition approaches for 2D materials synthesis, novel plasma-based physical vapor (PVD) techniques were used to fabricate uniform films over large areas. This experimental approach allowed unique studies. For example, vapor phase growth allowed systematically variation of the sulfur vacancy concentration in MoS2 and WS2 and subsequent correlation to electronic properties. This effort leads to controlled bottom-up assembly of 2D devices on flexible and standard substrates to experimentally couple the remarkable intrinsic mechanical and electronic properties of ultrathin materials, which are particularly appealing for molecular sensing. The pursuit of an all physical vapor deposited field effect transistor (FET) is the main priority for the 2D materials community as definitive demonstration of the feasibility of physical vapor deposition as a scalable technique for consumer electronics. PVD sputtered Titanium Nitride (TiN) and Tungsten (W) were experimentally characterized as potential back gated materials, Plasma Vapor Deposited (PLD) a-BN was electrically characterized as a uniform ultra-thin low temperature dielectric, and sputtered MoS2 and WS2 were electrically characterized as a semiconductor material. Tungsten deposition methods were previously researched and mimicked for smooth and conductive back gate material depositions. TiN was parameterized and the best room temperature deposition conditions were 70V applied to the sputtering gun with 25 sccm gas flow of 90% N2 and 10% Ar for 60 minutes. The best high temperature depositions were done at 500oC, 70V applied to the sputtering gun with 25 sccm gas flow of 90% N2 and 10% Ar for 30 minutes. Dielectric a-BN electrical characterization began to occur after 6nm which equated to 100 pulses, while 200 pulses equated to 16.5nm thickness. A dielectric constant of 5.90 ± .65 is reported for a-BN for under 20nm thickness. Soft probing techniques by conductively pasted gold wires on the probe tips were required to obtain true electrical measurements of 2D materials in a stacked structure, otherwise scratching would occur and uniformity would cease to exist in the film. Chemical Vapor Deposition (CVD) and mechanical exfoliation have provided the only working TMD semiconductor 2D materials in MOSFET structure to date with lithographic electrical connections. PVD sputtering as a new synthesis method for crystalline TMD with a stoichiometric ratio is achievable over large areas. Though, reduced area depositions are required for doped Silicon and Silicon Oxide (SiO2) based FET structures to limit the chance of encountering a pinhole. With reduced area and stoichiometric enhancement control, sputtered TMD films exhibit high sensitivity to oxygen and are electrically conductive even when exposed to a field effect. Increasing the grain size of the sputtered materials is the next driving force towards a fully recognizable TMD thin film transistor.

Committee:

Christopher Muratore, PhD (Committee Chair); Terrence Murray, PhD (Committee Member); Kevin Myers, DSc (Committee Member)

Subjects:

Aerospace Engineering; Aerospace Materials; Electrical Engineering; Engineering; Materials Science

Keywords:

PVD; materials; 2D materials; Nanoelectronics; TMDs; 2D Transistors; Molybdenum Disulfide; MoS2; WS2; Tungsten Disulfide

Harris, Tracey LynnElectrochemistry of trinuclear metal clusters of molybdenum and tungsten in 1-ethyl-3- methylimidazolium tetrafluoroborate
Master of Science (MS), Wright State University, 2008, Chemistry
The imidazolium based ionic liquid: 1-ethyl-3- methylimidizoliumtetrafluoroborate, (EMIBF4) was synthesized to be used as a solvent for the electrochemical investigation of molybdenum and tungsten. The electrochemical window is about 4.2V after removing traces of impurities such as Cl- and H2O. Electronic spectra of metal clusters [Mo3O2(O2CCH3)6(H2O)3]+2 ; [W3O2(O2CCH3)6(H2O)3]+2 ; [MoW2O2(O2CCH3)6(H2O)3]+2 and [Mo2WO2(O2CCH3)6(H2O)3]+2 in EMIBF4 are identical to the spectra of the same clusters obtained in water. Cyclic voltammogram (CV) of Mo and W clusters obtained in EMIBF4 are clearly dependant on the potential of working electrode. For example the CV of [Mo3O2(O2CCH3)6(H2O)3]+2 metal clusters on glassy carbon electrodes displays a reduction peak at ≈ +1.0V and a reversible oxidation peak at ≈ 1.8 - 2.0V and a reoxidation peak upon reversal of potential characteristic of deposition of metals on the Pt electrode. In this research we propose that during electrolysis, the clusters will be disintegrated during oxidation and the metal will be deposited onto the platinum electrode by reduction.

Committee:

Vladimir Katovic, PhD (Advisor); David Grossie, PhD (Committee Member); Suzanne Lunsford, PhD (Committee Member)

Subjects:

Chemistry

Keywords:

Metal Clusters; Tungsten; Molybdenum; Ionic Liquid

Woods, Matthew P.Activity and Selectivity in Oxidation Catalysis
Doctor of Philosophy, The Ohio State University, 2008, Chemical Engineering

In oxidation catalysis, a fine balance must be struck between catalyst activity and selectivity. The existence of complex networks of reactions involving oxygen can prove difficult to deal with and obtaining high activity in the desired reaction without undesired consecutive or parallel reactions is a major challenge. This research investigates the challenges associated with achieving high activity and selectivity in the oxidative dehydrogenation of ethane and the preferential oxidation of carbon monoxide in hydrogen rich streams.

Worldwide production of olefins exceeds that of any other chemicals and constitutes a sizable fraction of total petrochemical production. Traditional methods of olefin production require high temperatures, high energy input and are also limited by coke deposition and thermodynamic considerations. Oxidative dehydrogenation (ODH) is an alternate method of olefin production and does not suffer from the drawbacks of traditional methods. The major drawback of ODH is selectivity control. The olefin produced can easily react with oxygen to form the undesired combustion products CO2 and H2O.

In this work, the use of N2O as oxidant, rather than O2, in ethane ODH was investigated. A 10%Mo/Si:Ti catalyst was tested for ethane oxidative dehydrogenation (ODH) activity using either O2 or N2O as the oxidant. Ethane ODH activity was tested at contact times varying from 0.46 to 1.0 mg s cm-3. N2O gives superior ethylene selectivities at a given ethane conversion outperforming oxygen at all contact times tested. Ethylene selectivities decrease with contact time at a far slower rate when using N2O as the oxidant. XPS experiments demonstrate that molybdenum in the catalyst is fully oxidized to Mo(VI) during ethane ODH using O2 while the reduction state decreases to an average of +5.8 when using N2O as the oxidant. Temperature programmed oxidation experiments of pre-reduced 10%Mo/Si:Ti were carried out at different temperature ramp rates. The activation energy of reoxidation when using N2O is 98 kJ/mol while that of O2 is 41 kJ/mol leading to a reoxidation rate of at least 1700 times faster when O2 is the oxidant. This difference in rates accounts for the less oxidized state of molybdenum during ethane ODH with N2O and explains the behavior observed during reaction experiments. The concept of site isolation provides a satisfactory framework for understanding the steady state reaction results. Some carbon deposition was observed when using N2O as oxidant during ethane ODH as determined from post ODH TPO and XPS experiments but it did not affect ODH activity.

Proton exchange membrane (PEM) fuel cells promise to be clean and efficient alternatives to combustion of fuels for power generation. Unfortunately, the catalysts used in PEM anodes are easily poisoned by trace amounts of carbon monoxide. Reduction of the carbon monoxide concentration to a level of approximately 10 ppm is currently necessary to prevent this poisioning. Preferential oxidation of carbon monoxide (PROX) offers an economic and simple method of CO removal but in high concentrations of hydrogen maintaining a high catalyst activity and selectivity simultaneously can be problematic due to unselective H2O oxidation and CO methanation.

This work demonstrates the preparation of a 10%CoOx/CeO2 catalyst that is highly effective for the preferential oxidation of carbon monoxide in a hydrogen rich feed. The CoOx/CeO2 catalyst had a high surface area of 78m2/g and was able to maintain a near 100% CO conversion while maintaining a selectivity of 58% during PROX experiments in high concentrations of hydrogen. The catalyst is able to obtain high CO conversions under a wide range of weight hourly space velocities. Introducing H2 into the feed has a negative effect on the CO consumption rate and decreases O2 selectivity to CO2. This shows that the reaction rates for CO oxidation and H2 combustion are not independent and suggests that hydrogen may competitively adsorb on sites responsible for CO oxidation. Separate H2 and CO oxidation experiments give activation energies of 74 and 52 kJ/mol, respectively. Additionally, the preexponential factor for H2 is 25 times higher than that for CO under the reaction conditions employed. It is possible that there are more sites available for H2 oxidation but this reaction requires high temperatures to occur at appreciable rates. Temperature programmed PROX reaction experiments show three temperature regions where different reactions are important. Below 175°C, CO oxidation is dominant but above this temperature, CO oxidation and H2 combustion compete with one another. The temperature necessary to obtain high activity in the PROX reaction occur near this transition at 175°C. At even higher temperatures, irrelevant to the PROX reaction, methanation begins to occur. Raman spectroscopy and X-ray diffraction experiments have demonstrated that the cobalt takes the form of Co3O4 and no CoO was detected under any experimental conditions.

Committee:

Umit Ozkan (Advisor); Jeffrey Chalmers (Committee Member); James Rathman (Committee Member)

Subjects:

Chemical Engineering

Keywords:

oxidative dehydrogenation; ODH; molybdenum; silica; titania; nitrous oxide; N2O; reoxidation; site isolation; temperature programmed oxidation; TPO; preferential CO oxidation; PROX; cobalt; ceria; Co3O4; CeO2; H2 oxidation; TPR

Lee, JaesungOptically Transduced Two-Dimensional (2D) Resonant Nanoelectromechanical Systems and Their Emerging Applications
Doctor of Philosophy, Case Western Reserve University, 2017, EECS - Electrical Engineering
Two-dimensional (2D) crystals, derived from layered materials and consisting of atomically thin sheets with weak van der Waals interlayer interactions, have been the subject of many exciting research efforts, including discoveries of new device physics and explorations of creating novel devices for future applications. In addition to excellent electrical and optical properties in their atomically thin limit, 2D crystals also intrinsically possess excellent mechanical properties (e.g., high strain limit of ~25%, and Young’s modulus of EY~1TPa for graphene), making them attractive candidates for next generation nanoelectromechanical systems (NEMS). Initial studies on 2D NEMS have mostly been focused on the semimetal graphene, where challenges remain in device performance (e.g., low quality factors) and practical applications (e.g., sensors and oscillators). Meantime, remarkable opportunities are emerging for the new 2D semiconductors. This dissertation presents investigations of both fundamental device physics and engineering of device functions and performance toward the perspective of technological applications. This dissertation includes: (i) study of frequency scaling of 2D NEMS resonators for providing an important guideline to achieve 2D resonators with desired resonance frequency; (ii) investigation of air damping in 2D NEMS to evaluate performance of resonators when they are operating in air which may be exploited for applications in gas and pressure sensing; (iii) experiments on frequency tunability for creating highly tunable resonant 2D NEMS, which may enable applications in voltage controlled oscillators; and (iv) demonstration of parametric amplification for greatly boosting the relatively low initial Q values of 2D NEMS resonators. Based on the aforementioned fundamental device physics and engineering studies, 2D NEMS have been explored and their potential has been evaluated for future applications in sensing and radio-frequency (RF) signal processing. By integrating passive 2D NEMS into an optical and electrical combined circuitry, self-sustained feedback 2D NEMS oscillators have been created; and positive feedback and feedback cooling have been explored for RF signal processing applications. In addition, as proof-of-concept studies with potential for sensing applications, the effects of pressure variations and gamma-ray radiation upon the 2D NEMS have been tested, and excellent responsivities and sensitivities for potential sensing capabilities have been achieved. The findings in this dissertation may provide import understandings of 2D NEMS, and help pave the way for transforming 2D NEMS resonators into relevant emerging applications.

Committee:

Philip Feng (Committee Chair); Christian Zorman (Committee Member); John Lewandowski (Committee Member); Hongping Zhao (Committee Member)

Subjects:

Electrical Engineering

Keywords:

NEMS; MEMS; Resonator; Oscillator; 2D Materials; Molybdenum Disulfide; MoS2; Graphene

Murphy, Neil RichardReactive sputtering of mixed-valent oxides: a route to tailorable optical absorption
Doctor of Philosophy (Ph.D.), University of Dayton, 2015, Materials Engineering

This work details two specific research thrusts exploring the deposition and characterization of mixed valent oxide systems. The first of these thrusts investigated the effect of the oxygen content, during reactive sputter deposition, on the optical, chemical, and structural properties of oxides of molybdenum, germanium, and rhenium. Exploration of the Mo-O system was conducted using a technique known as modulated pulse power magnetron sputtering (MPPMS), while the Ge-O and Re-O systems were deposited via direct current magnetron sputtering (DCMS). Films deposited under poisoned mode conditions were shown to be highly transparent with refractive index (n) values of n550=1.60 for GeO2, and n550=1.97 for MoO3, similar to values reported for bulk constituents. The Re-O system, unlike Ge-O and Mo-O, displayed a significantly high sensitivity to ambient moisture. Chemical analysis via XPS indicated the presence of instability as a result of the moisture induced decomposition of Re2O7 into HReO4, and catalytic disproportionation of Re2O3 into Re and hydrous ReO2.

The second research thrust within this project was focused on the deposition of three component mixed oxide systems with multiple valence states. This effort, which utilized the results from individual material depositions mentioned previously, required the use of stable and thermodynamically compatible material systems, namely Mo-O and Ge-O (ΔfHo(MoO2)= -588 kJ/mol and ΔfHo(GeO2)= -580 kJ/mol). Note that Re-O was not explored as part of the ternary deposition effort due to the aforementioned chemical instability. To achieve the goal of depositing mixed valent thin films with tailorable optical absorption, an industrially scalable co-deposition method was devised in order to deposit molybdenum cations within a dielectric GeO2 matrix. The high power densities associated with the MPPMS process were systematically varied in order to control the oxygen partial pressure via gettering, allowing for control over the oxidation state and concentration of Mo4+ (MoO2) and Mo3+ (Mo2O5) cations within a transparent GeO2 matrix. In addition, this work devised a modification to the Berg model for reactive sputtering that is capable of predicting the resulting oxidation states of Mo and Ge within a reasonable degree of accuracy. The co-deposition procedure devised within this work allowed for the optical gap of mixed MoxGeyOz films to be tailored between 3.4 eV and 0.4 eV, spanning useful ranges for devices operating in the visible and near-infrared.

Committee:

P. Terrence Murray, Ph.D. (Committee Chair); Dean R. Evans, Ph.D. (Advisor); John T. Grant, Ph.D. (Committee Member); Daniel P. Kramer, Ph.D. (Committee Member); Andrew M. Sarangan, Ph.D. (Committee Member)

Subjects:

Materials Science

Keywords:

magnetron sputtering; thin film deposition; ellipsometry; optical coatings; x-ray photoelectron spectroscopy; XPS; optical absorption; band gap tailoring; molybdenum oxide; germanium oxide; Mo-Ge-O; mixed oxide coatings; reactive sputtering

Wang, YiminReactive Sputter Deposition of Molybdenum Nitride Thin Films
MS, University of Cincinnati, 2002, Engineering : Materials Science

Molybdenum nitride thin film was deposited on silicon wafer by the reactive sputter deposition. Single phase γ–Mo2N thin film was obtained with N2/(Ar+N2) flow ratios in sputtering gas varying from 10% to 30% whereas an amorphous structure was obtained at N2/(Ar+N2) flow ratios of 50%.

The deposition rate of the molybdenum nitride thin film varies significantly as nitrogen partial pressure in sputtering gas increases. A decrease in peak intensity along with peak shift and broadening was observed in X-ray diffraction spectra as the nitrogen partial pressure sputtering gas increased. The XPS analysis of the as-deposited thin films shows that the Mo 3d3/2, Mo 3d5/2 and Mo 2p3/2 peak gradually shift to the higher binding energy direction as nitrogen partial pressure is increasing. The intensity of N 1s peak also increase with increasing nitrogen partial pressure. Although the XRD examination shows no evidence of long range order of the phase structure for the amorphous thin film sputtered at 50% N2/(Ar+N2) flow ratio, the existence of Mo–N bond in the film was confirmed by XPS examination. The nitrogen partial pressure in the sputtering gas was found to have significant influence on the surface morphologies and cross section structures of the thin film.

Thermal annealing of the amorphous thin film in a nitrogen atmosphere revealed that the film could survive 700°C/5min thermal annealing without obvious crystallization but failed after 800°C/5min thermal annealing, in which the crystalline γ-Mo 2N and h–MoSi2 phases were observed simultaneously.

Committee:

Dr. Ray Y. Lin (Advisor)

Subjects:

Engineering, Materials Science

Keywords:

molybdenum nitride; sputter deposition; thin film; amorphous; nitrogen partial pressure

Liu, ChangThe spectroscopic and structural characterization of chlorine modification of MoOx catalysts supported over silica/titania mixed oxides for the oxidative dehydrogenation of ethane and propane
Doctor of Philosophy, The Ohio State University, 2004, Chemical Engineering
In this study, the use of molybdenum catalysts supported over silica-titania mixed-oxides has been investigated in regard to their activity for the oxidative dehydrogenation (ODH) of ethane and propane. The incorporation of chlorine was able to improve the ethylene and propylene formation rates up to Cl/Mo=2.0. The effect of chlorine dopants on the catalyst surface characteristics and, in turn, on the catalytic performance in ethane and propane ODH has been examined. The catalysts used in this study have been synthesized by a modified "one-pot" sol gel/co-precipitation technique. The main focus of the work has been characterization of the surface molybdena species, physical-chemical properties of the Si:Ti support, reducibility, adsorption/desorption behavior, and surface intermediates present during the reaction. Catalysts were characterized by physical adsorption, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), laser Raman spectroscopy (LSR), diffuse reflectance infrared fourier transform spectroscopy (DRIFTS), temperature programmed reduction (TPR), temperature programmed desorption/reaction (TPD/TPrxn), electron spin resonance (ESR), secondary ion mass spectrometry (SIMS), and steady-state isotopic transient kinetic analyses (SSITKAS). The characterization results are correlated to the catalytic performance to achieve a better understanding of chlorine-modified catalysts.

Committee:

Umit Ozkan (Advisor)

Subjects:

Engineering, Chemical

Keywords:

Spectroscopic; Chlorine; Molybdenum; Silica/Titania; Oxidative Dehydrogenation; Ethane; Propane

Pauff, James MichaelStructure-Function Studies of Xanthine Oxidoreductase
Doctor of Philosophy, The Ohio State University, 2008, Integrated Biomedical Sciences
Xanthine oxidoreductase (XOR) is a 290 kDa molybdenum-containing enzyme that catalyzes the final two steps in human purine catabolism, taking hypoxanthine to xanthine and then on to uric acid. The enzyme exists as a homodimer, with each monomer possessing a catalytic active site that contains one molybdenum atom coordinated to a pterin ring via an enedithiolate side chain. Each monomer also contains two [2Fe2S] clusters and one equivalent of FAD. These centers form an electron transfer chain as electrons are passed sequentially from the molybdenum to the FAD via the iron-sulfur clusters. The molybdenum center cycles from MoVI to MoIV and back during catalysis, passing through an occasional MoV intermediate state. Electrons are passed from the flavin site out of the enzyme to either NAD+ or molecular oxygen. XOR is initially expressed as a dehydrogenase (xanthine dehydrogenase, XDH) with a strong preference for reducing NAD+ to NADH, although it can reduce O2 under conditions of low NAD+ concentrations. Under certain conditions, XDH can be converted by oxidation and/or limited proteolysis to an oxidase form (xanthine oxidase, XO) that utilizes O2 exclusively as the terminal electron acceptor, thereby generating superoxide and other reactive oxygen species. The oxidase is formed primarily during hypoxia or ischemia, and the corresponding increase in reactive oxygen species has lead to investigation of the enzyme’s role in the pathophysiological mechanism of ischemia-reperfusion. The production of uric acid by XOR makes the enzyme a primary target in hyperuricemia, and it is this therapeutic intervention for which allopurinol has been used for over 60 years. The prevalence of XOR in mechanisms leading to some human diseases and the unique chemistry by which the enzyme catalyzes the production of uric acid makes this enzyme system an interesting subject of biochemical investigation. We have sought here to understand the structure and function of xanthine oxidoreductase, focusing on the nature of the molybdenum-containing active site as well as innate functional differences between the two forms of the enzyme. Our crystallographic and spectroscopic studies provide insight into the mechanism of XOR catalysis as well as the roles of XOR in human pathology.

Committee:

Virginia Sanders, PhD (Advisor); Russ Hille, PhD (Advisor); Allan Yates, MD, PhD (Committee Member); Charles Bell, PhD (Committee Member); Patrick Roblin, PhD (Other)

Subjects:

Biochemistry; Biomedical Research; Neurology; Pathology

Keywords:

Xanthine Oxidase; Enzme Catalysis; Molybdenum; Metalloenzyme

Mallik, SankuChemistry of enolates on organo-molybdenum complexes
Doctor of Philosophy, Case Western Reserve University, 1992, Chemistry
Asymmetric deprotonation of the prochiral ketone 1 was studied using a variety of chiral secondary lithium amide bases. The lithium amide 2 furnished the monomethylated complex 3 in 40% optical purity. The absolute stereochemistry of 3 is not known.(DIAGRAM, TABLE OR GRAPHIC OMITTED...PLEASE SEE DAI). Properties of the ketones 4 and 5 were studied to determine the relative effects of the steric bulk of the metal and the conformations of the molecules in determining their reactivities.(DIAGRAM, TABLE OR GRAPHIC OMITTED...PLEASE SEE DAI)For the complex 4, enolization and subsequent alkylation at C-4 was facile and the stereochemistry was controlled by the steric bulk of the Mo(CO)2Cp moiety. However, for nucleophile additions to the carbonyl group at C-5, the conformation of the molecule was the major factor in directing the stereochemistry of the products.

Committee:

Anthony Pearson (Advisor)

Subjects:

Chemistry, Organic

Keywords:

Enolates; Organo-molybdenum complex

Shiller, Paul JosephReactions of methanol and carbon monoxide on ad-atom modified platinum(111) and molybdenum(110) surfaces: Molecular orbital study
Doctor of Philosophy, Case Western Reserve University, 1991, Chemistry
The oxidation of methanol to carbon dioxide is an important industrial process. Although a great deal of information is known about the entire oxidation process the individual steps of the process are not so well known. Each step on the surface is affected by the surface composition. Methanol reacts on late transition metal surfaces to ultimately yield CO and H2. In this thesis, various aspects of methanol oxidation on metal surfaces are explained with the atom superposition and electron delocalization molecular orbital (ASED-MO) method. In addition, bonding in transition metal disilyl complexes was studied. The activation barrier to the dehydrogenation of adsorbed methoxy is calculated to be less on a clean Pt surface than on an O covered Pt surface because the reaction on the O covered surface requires the electron transfer from the relatively low lying O 2p lone pair orbitals to the metal Fermi level. In the case of the clean surface there is no net electron transfer merely the rearrangement of the electrons at the Fermi level. The O stabilizes the adsorbed methoxy towards dehydrogenation. On a Mo surface adsorbed CH3O has been observed to decompose to CH3cdot and O(ads). Compared to the strong C-O bond in methan ol formed by binding CH3cdot to OH, the binding of CH3 to O2- on the Mo surface generates an electron which is promoted to the surface conduction band, weakening the C-O bond strength. This explains the thermal desorption results of Serafin and Friend, who observed CH3cdot(g) formation on heating a Mo(110) surface with adsorbed methoxy. Ad-atoms can affect the reaction rate of methanol on electrode surfaces. Sn increases the oxidation rate of methanol significantly. In our work, Ge, Sn, and Pb adsorbed onto a Pt surface are found to reduce the chemisorption energy of CO. Oxidation of the ad-atoms by binding OH to them only slightly reduces the effect while oxidation by O cancels it. When these atoms are placed substitutionally in the Pt surface the effect is small. The effect stems from a CO 4σ-Sn 5s closed-shell repulsion through the Pt surface atoms. The through space repulsion is negligible.

Committee:

Alfred Anderson (Advisor)

Subjects:

Chemistry, Physical

Keywords:

methanol; carbon monoxide; ad-atom modified platinum(111); molybdenum(110); surfaces; Molecular orbital study

Kennedy, Edward NelsonThe Electrochemical Behavior Of Molybdenum And Tungsten Tri-Nuclear Metal Clusters With Ethanoate Ligands
Doctor of Philosophy (PhD), Wright State University, 2017, Environmental Sciences PhD
The goal of this research was to study the electrochemical behavior of tri-nuclear clusters of molybdenum and tungsten. In addition, the feasibility of using these clusters as catalysts for the purpose of oxidizing ethanol was investigated. Four tri-nuclear cluster compounds were studied: hexa-µ2-acetatotriaquadi-µ3-oxotrimolybdenum (IV, IV, IV) trifluoromethanesulfonate [Mo3O2(O2CCH3)6(H2O)3](CF3SO3)2, hexa-µ2-acetatotriaquadi-µ3-oxodimolybdenum (IV, IV) tungsten (IV) trifluoromethanesulfonate [Mo2W2O2(O2CCH3)6(H2O)3](CF3SO3)2, hexa-µ2-acetatotriaquadi-µ3-oxomolybdenum (IV) ditungsten (IV, IV) trifluoromethanesulfonate [MoW2O2(O2CCH3)6(H2O)3](CF3SO3)2, and hexa-µ2-acetatotriaquadi-µ3-oxotritungsten (IV, IV, IV) trifluoromethanesulfonate [W3O2(O2CCH3)6(H2O)3](CF3SO3)2. Data was gathered from experimental results with cyclic voltammetry for the four tri-nuclear clusters. Initially, an ionic liquid, EMIBF4 (1-ethyl-3-methylimidazolium tetrafluoroborate), was used as the solvent. Subsequent solvents for use with these clusters were investigated, including ACN (acetonitrile) and NMF (N-methylformamide). The secondary solvent system settled on was the DMSO-TBAHFP solvent system. Each tri-nuclear cluster displayed a reversible redox reaction and one or more irreversible reduction reactions. The redox peak potentials were found to be Ep,a: -0.44V and Ep,c: -0.42V for Mo3, Ep,a: -0.32V and Ep,c: -0.43V for Mo2W, Ep,a: -0.31 V and Ep,c: -0.44 V for MoW2, and Ep,a: -0.42 and Ep,c: -0.46 for the W3 tri-nuclear cluster. The irreversible reduction reactions for each tri-nuclear cluster were observed at Ep,c(2): -0.74 for Mo3, Ep,c(2): -1.15 for Mo2W, Ep,c(2): -1.14 for MoW2, and Ep,c(2): -0.84 for the W3 tri-nuclear cluster. The diffusion coefficients in DMSO were determined to be DMo3 = 9.105E-06 cm2s-1, DMo2W = 1.743E-05 cm2s-1, DMoW2 = 1.764E-05 cm2s-1, and DW3 = 1.991E-05 cm2s-1. Exploring the electrocatalytic capability of these compounds was another effort made, by attempting to electroplate the compounds on platinum electrodes. Although some types of deposition events did appear to occur, it is unlikely they were of the intact tri-nuclear clusters. Thus far, the ethanol molecule has been partially oxidized, but breaking the carbon-carbon bond in the molecule proved to be a challenge that was not achieved.

Committee:

Vladimir Katovic, Ph.D. (Advisor); Jay Johnson, Ph.D. (Advisor); Suzanne Lunsford, Ph.D. (Committee Member); William Heineman, Ph.D. (Committee Member); Christopher Barton, Ph.D. (Committee Member); Doyle Watts, Ph.D. (Committee Member)

Subjects:

Alternative Energy; Chemistry; Environmental Science; Materials Science

Keywords:

Tri-nuclear clusters; diffusion coefficient; cyclic voltammetry; electrodeposition; molybdenum; tungsten

Lee, Edwin WendellGrowth and Nb-doping of MoS2 towards novel 2D/3D heterojunction bipolar transistors
Doctor of Philosophy, The Ohio State University, 2016, Electrical and Computer Engineering
Molybdenum disulfide (MoS2) is a member of a group of layered materials called transition metal dichalcogenides (TMDs) characterized by monolayers consisting of a transition metal atom (Mo or W for example) sandwiched between chalcogen atoms (S, Se, Te) on either side. The monolayers have no out-of-plane bonds and bulk TMDs consist of many monolayers stacked and held together weakly by van der Waals forces. Bulk MoS2 exhibits an indirect band gap of 1.2 eV, but monolayer films exhibit a direct gap of 1.8 eV. MoS2 has been studied for a wide range of applications, many by utilizing micromechanically exfoliated, micron-scale flakes to study its material properties. Study of these flakes points to scaling limitations, and many groups have explored large-area growth methods to produce high-quality, continuous films. This work aims to demonstrate traditional device engineering based on MoS2 including growth, doping, heterostructure study and device design. We demonstrate single crystal growth of MoS2 by depositing Mo on sapphire substrates and sulfurizing the samples in a chemical vapor transport process. The growth process is robust, and reasonably could be scaled up to wafer-scale processing. The films exhibited excellent structural qualities, and electrical measurements showed high space-charge mobility. The MoS2 films were also doped with Nb in order to achieve p-type mobility. Degenerate doping of the films was demonstrated and confirmed by low temperature Hall measurement, and film conductivity increased by four orders of magnitude over unintentionally doped films. The degenerately doped films were shown to exhibit a Hall mobility of approximately 10 cm2V-1s-1. Heterojunction diodes were formed between degenerately doped p-MoS2¬ and n-doped SiC and GaN by direct growth and film transfer, respectively, to form 2D/3D heterojunctions. Electrical measurements were utilized to extract the conduction band offsets in MoS2/SiC (¿EC = 1.6 eV) and MoS2/GaN (¿EC = 0.2 eV) junctions. Characterization of the heterostructures showed that traditional 3D semiconductor methods are sufficient to characterize the 2D materials despite the van der Waals gaps between each MoS2 monolayer. The MoS2/GaN heterojunction was used as the base/collector junction for a tunneling heterojunction bipolar transistor (THBT) for which the emitter was atomic layer deposited Al2O3. THBTs showed small common base gain corresponding with positive transconductance in the common emitter configuration. As such, the MoS2/GaN heterojunction shows significant promise for future HBT applications.

Committee:

Siddharth Rajan (Advisor); Aaron Arehart (Committee Member); Roberto Myers (Committee Member)

Subjects:

Engineering

Keywords:

MoS2; Molybdenum disulfide; Doping; 2D-3D; Heterojunction; heterojunction bipolar transistor; transition metal dichalcogenide; 2D materials;

Khatri, HimalNew Deposition Process of Cu(In,Ga)Se2 Thin Films for Solar Cell Applications
Doctor of Philosophy, University of Toledo, 2009, Physics
Molybdenum (Mo) is currently the most common material used for Cu(In,Ga)Se2 solar cell back contacts. The first objective of this study is to utilize in–situ and ex–situ characterization techniques to investigate the growth, as well as the physical and chemical properties, of Mo thin films deposited by RF magnetron sputtering onto soda–lime glass (SLG) substrates. The effects of the deposition pressure on the nucleation and growth mechanisms that ultimately influence morphology and grain structure have been studied. Correspondence between real time spectroscopic ellipsometry (RTSE), X–ray diffraction (XRD), atomic force microscopy (AFM), and four–point probe resistivity measurements indicate that increasing deposition pressure leads to smaller average grain sizes and higher oxygen content in the Mo thin films. Changes of the material properties were also evaluated by changing RF power. It is observed that higher RF power, results in higher conductivity films. The second and overall objective of this work is to focus on the deposition and characterization of the Cu(In,Ga)Se2 absorber layer using the hybrid co–sputtering and evaporation process, which has potential for commercial PV. Solar cells were completed with a range of elemental compositions in the absorber layer, keeping a constant profile of Ga and varying Cu concentrations. The slightly Cu deficient Cu(In,Ga)Se2 films of band gap ~1.15 eV fabricated by this process consist of a single chalcopyrite phase and device efficiencies up to 12.4% were achieved for the composition ratios (x, y) = (0.30, 0.88). Correspondence between energy dispersive X–ray spectroscopy (EDS), X–ray diffraction, transmission and reflection (T&R), four–point probe resistivity, and current density–voltage (J–V) measurements indicate that increased Cu concentration leads to the incorporation of a secondary phase Cu2-xSe compound in the Cu(In,Ga)Se2 films, which is detrimental to cell performance. The third objective of this work is to evaluate the Cu2-xSe material properties by employing in–situ RTSE, as well as ex–situ SE and various other characterization techniques. SE revealed that the dielectric function spectra of Cu2-xSe evolve with temperature, providing insights into the evolution of transport properties and critical point structures. At room temperature, semi–metallic behavior of Cu2-xSe thin films was revealed by SE and Hall Effect measurements. These characteristics serve as key inputs for optical modeling of complex layer structures of Cu(In,Ga)Se2 films grown by 2– and 3–step processes.

Committee:

Sylvain Marsillac, Ph.D. (Advisor); Terry Bigioni, Ph.D. (Committee Member); Jon Bjorkman, Ph.D. (Committee Member); Robert Collins, Ph.D. (Committee Member); Michael Heben, Ph.D. (Committee Member)

Subjects:

Energy; Engineering; Materials Science; Physics

Keywords:

Cu(In,Ga)Se2; CIGS; Cu2-xSe; Hybrid co-Sputtering; Evaporation; Ellipsometry; Molybdenum; Optical Properties

Li, BohaoRoom Temperature Processed Molybdenum Oxide Thin Film as a Hole Extraction Layer for Polymer Photovoltaic Cells
Master of Science in Engineering, University of Akron, 2013, Polymer Engineering
A room-temperature processed molybdenum oxide ultra-thin film as a hole transport layer in bulk heterojunction was successfully made and demonstrated. No doubts the discovery of this technique will stimulate the study on polymer photovoltaics and eventually boost its application in industry for large-scale production.

Committee:

Xiong Gong, Dr. (Advisor); Alamgir Karim, Dr. (Committee Member); Yu Zhu, Dr. (Committee Member)

Subjects:

Chemistry; Physics; Polymers

Keywords:

Polymer solar cells; hole transporting; molybdenum oxide; device characterization; room-temperature processing.

Kim, Yeong HoChromium-free consumable for welding stainless steel: corrosion perspective
Doctor of Philosophy, The Ohio State University, 2005, Materials Science and Engineering
Arc welding of stainless steels generates welding fumes containing carcinogenic hexavalent chromium. To mitigate this problem, a Cr-free filler metal needs to be developed to reduce the health risks for welding stainless steel. Ni-Cu alloy, Monel K400, was selected initially based on its galvanic compatibility with types 304 and 316 SS in chloride environments Type 304L (UNS S30403) stainless steel plate was successfully welded with Monel filler wire, resulting in high quality welds with no cracks. The welds survived long term exposure in 0.1 M NaCl with no evidence of corrosion. However, segregated regions in weld that are rich in Cu are the weak spots for corrosion susceptibility. The effects of alloying elements on the corrosion properties of Ni-Cu alloy were investigated to optimize the composition of a Cr-free consumable for welding of stainless steels. Cyclic polarization experiments were performed in 0.1 M NaCl on Ni-base alloys containing different amounts of Cu, Pd, Mo, Fe, and Cr. The localized corrosion behavior improved as the Cu content decreased from 30 to 5 wt%. The addition of 1 wt% Pd ennobled the alloy and greatly improved the localized corrosion properties. The optimized composition is a Ni-based alloy containing 5-10 wt% Cu and 1 wt% Pd. Ni-10Cu-1Pd alloy across the entire dilution range exhibited higher repassivation potential than Type 304L stainless steel in 0.1 M NaCl solution. The repassivation potential was also higher in aerated solutions with chloride concentrations of 105 through 35000 ppm. The breakdown behavior of Bead-On-Plate weld was similar to that of Type 308L welds. After 31 days exposure of samples with crevice-formers in 500 and 1000 ppm chloride solutions, the Bead-On-Plate weld showed much shallower attack than the 308L weld. The passive film on Ni-10Cu-1Pd alloy mainly consisted of outer Ni-hydroxide and inner oxide, but the noble elements of Pd and Cu did not contribute to the formation of the passive film. However, Pd catalyzed the reduction of Cu at the bottom of the artificial pit, which enhanced the cathodic reaction and thus ennobled the deactivation potential making stable pit growth more difficult.

Committee:

Gerald Frankel (Advisor)

Subjects:

Engineering, Materials Science

Keywords:

stainless steel; corrosion; weld; hexavalent chromium; nickel; alloy; copper; palladium; molybdenum; dilution; segregation; localized corrosion; breakdown; artificial pit electrode; repassivation; deactivation

Hollandsworth, Carl B.Full and half sandwich compounds of dimolybdenum and ditungsten
Doctor of Philosophy, The Ohio State University, 2004, Chemistry

There are a very small number of structurally-characterized sandwich compounds of the type M2L2 where M = Mo, W and L = a (CH2)n carbocyclic ring. This is in contrast to the large number of mononuclear compounds of the same type. This interesting disparity may be a result of insufficient synthetic attempts to make such compounds rather than some inherent instability of the M2(carbocycle)2 species.

A new family of half-sandwich complexes of ditungsten alkoxides is defined as structures having the formula W2(carbocycle)(OR)4. Attempts to make such compounds via the alcoholysis of 1,2-W2Cp2(NMe2)4 were unsuccessful. 1,2-W2Cp2(NMe2)4 shows a unique resistance among dimethylamide compounds of tungsten towards alcoholysis with the typical aliphatic alcohols used in such reactions. Strongly acidic alcohols, such as CF3CH2OH, are required to react with this dimethylamide. These reactions lead to over-alcoholysis products such as 1,1 W2Cp(η3-C5H7)(OCH2CF3)6.

Unlike W2Cp2(NMe2)4, W2COT(NMe2)4 undergoes facile alcoholysis to form [W2COT(OR)4]n species where n = 1 for R = tert butyl, isopropyl, and neopentyl and n = 2 for R = Me, Et, and Pr. The dinuclear alkoxides exhibit a fluxional COT ligand which rotates about the W-W bond via a 1,2-alkyl exchange mechanism. Two strong and symmetrical W-OR-W alkoxide bridges between two W2COT(OR)3 fragments are found within the tetranuclear compounds.

Several attempts to make sandwich compounds of ditungsten of stoichiometry W2COT2 were unsuccessful. Reactions of K2COT with quadruply-bonded W2Cl4(PR3)4 species lead to ill-defined species. Reactions of the Mo2(O2CCH3)4 paddlewheel compound with two equivalents of K2COT″ where COT″ = 1,4-bis-trimethylsilyl-1,3,5,7-cyclooctatetraene resulted in the formation of M2COT″3 compounds, despite the use of a bulky cyclooctatetraene ligand. Attempts to react the W4(OPr)16 cluster with two equivalents of Li2COT lead to reduction of the cluster and formation of two equivalents of Li2W2(OPr)8. DFT computational studies are used to explain the instability of W2COT2 sandwich compounds having both D8h and D2h symmetry. The same studies predict that (M2COT2)2+ species might be quite stable.

DFT computational studies of W2(benzene)2 sandwich compounds indicate that the W-W bridging, antifacial D2h structure is more stable than the D8h nonbridged and D2h synfacial structures. W2(benzene)2 compounds are expected to be stable. A suitable synthetic route to these compounds might be the reaction of metal atoms with immobilized arenes or M(arene)2 compounds.

Committee:

Malcolm Chisholm (Advisor)

Subjects:

Chemistry, Inorganic

Keywords:

tungsten; molybdenum; ditungsten; dimolybdenum; DFT; density functional theory; sandwich; COT; cyclooctatetraene; benzene

Hood, Brian L.Kinetic and spectroscopic characterization of members of the sulfite oxidase family of mononuclear molybdenum enzymes
Doctor of Philosophy, The Ohio State University, 2003, Ohio State Biochemistry Program
Enzymes that possess mononuclear molybdenum can be classified into three distinct families based on their active site geometry, molybdenum coordination and the number of equivalents of a unique pyranopterin cofactor. In the present work, several members of the sulfite oxidase family of mononuclear molybdenum enzymes have been spectroscopically and kinetically investigated to provide a deeper understanding of the nature of catalysis and electron transfer between the various redox-active centers these enzymes possess. A novel sulfite oxidase from Arabidopsis thaliana has been characterized and shown to be a true sulfite oxidase. This enzyme is a 43-kDa monomer that contains a single equivalent of the molybdopterin cofactor and no other redox-active centers. This is in contrast to other members in the sulfite oxidase family that typically contain heme domains. The plant enzyme is shown to catalyze the oxidation of sulfite to sulfate with similar kinetics as enzymes from mammalian sources, however does so with a significantly faster reductive half-reaction. In addition, the A. thaliana sulfite oxidase exhibits similar EPR features to other sulfite oxidases, and resonance Raman reveals peaks representative of an LMoO2(S-Cys) active site with a single pyranopterin cofactor. Catalytic turnover experiments with mouse sulfite oxidase in 18O-labeled water have established that the source of oxygen incorporated into product is derived from solvent and not dioxygen. This observation supports the findings seen for members of the other mononuclear molybdenum enzyme families. The crystal structure for chicken sulfite oxidase revealed that the heme domain is approximately 32 Å from the molybdenum center, and not opposite the pyranopterin cofactor as would be expected. This distance does not correlate to the observed rate of electron transfer between the two domains, hence it is likely that the heme domain may be significantly mobile during catalytic turnover. Initial experiments using NMR spectroscopy have revealed conditions that will allow for the determination of the dynamic nature of the heme domain under catalytic conditions. Investigation of several constructs of spinach assimilatory nitrate reductase mutants in the flavin domain of spinach assimilatory nitrate reductase has yielded information on the nature of electron transfer. Steady-state and rapid-reaction kinetics of these substrate-binding pocket mutants has revealed catalytic roles for each. Additionally, formation of the long-wavelength charge-transfer complex between reduced flavin and NAD+ has been shown for all mutants. A possible new function for this complex in electron transfer between the flavin and heme domains is suggested. Lastly, cDNAs encoding the human and chicken xanthine dehydrogenase enzymes have been cloned, expression systems have been developed and a number of active site mutants have been generated to investigate their roles in catalytic turnover. These systems will allow investigation of the various redox-active centers that these enzymes possess for a more complete understanding of the detailed mechanism of electron transfer between them.

Committee:

Russ Hille (Advisor)

Subjects:

Chemistry, Biochemistry

Keywords:

molybdenum; sulfite oxidase; nitrate reductase

Poerschke, David L.Mechanical Properties of Oxide Dispersion Strengthened Molybdenum Alloys
Master of Sciences (Engineering), Case Western Reserve University, 2009, Materials Science and Engineering
Lanthanum oxide dispersion strengthened (ODS) molybdenum has excellent high temperature properties but low ductility. The effect of heat treatment on the mechanical properties and formability of ODS-Mo sheet has been investigated in the temperature from 1500°C to 1800°C. Mechanical tests included three point bending, high temperature tensile testing, and hardness testing. Optical metallography, SEM, and TEM were used to evaluate the microstructure for each heat treatment condition. The 1500°C heat treatment temperature led to cracking due to incomplete transformation to a stress relieved structure. Samples treated at 1800°C produced 90° bends but the bend surfaces of samples treated for long time at this temperature were not smooth. Heat treated samples had lower YS and UTS than the as-rolled material. Grain growth along the rolling direction was faster than along transverse directions. This behavior is explained by the banding of oxide particles along the rolling direction.

Committee:

David Schwam, PhD (Advisor); John Lewandowski, PhD (Committee Member); Gerhard Welsch, PhD (Committee Member)

Subjects:

Materials Science; Metallurgy

Keywords:

molybdenum; ODS; ductility; oxide dispersion strengthening; high temperature

Maloy, Stuart AndrewDislocations and mechanical properties of single crystal molybdenum silicide
Doctor of Philosophy, Case Western Reserve University, 1994, Materials Science and Engineering
Dislocations and mechanical properties of single crystal MoSi2 have been investigated. Specimens were tested in compression along (001), (021), and (771) axes at strain rates of 1 × 10-4/s and 1 × 10-5/s and at temperatures ranging from 900-1600°C in vacuum or argon. The yield stress along (001) was an order of magnitude greater than that measured along (021) or (771) and along all orientations the yield stress was strongly dependent on temperature. Rate jump tests performed along (001) at 1400°C revealed that the yield stress was rate sensitive with a stress exponent of 4. The activated slip systems were determined using optical slip trace analyses and techniques in transmission electron microscopy. Slip occurred via five different slip systems (11<100>, 13<100>, 1001/2<111>, 131/2<331>, and 111/2<111>) depending on the orientation, temperature and strain rate at which each test was performed. The critical resolved shear stress was determined for the activated slip systems from the measured 0.2% yield stresses. At 900-1100°C, the lo west critical resolved shear stresses were for slip on the 11<100>, 1101/2<111> and 131/2<331> slip systems while at 1200-1600°C the lowest critical resolved shear stresses were for slip on the 11<100> and the 13<100> slip systems. Decompositions and dissociations of 1/2<331> and 1/2<111> dislocations were observed. The 1/2<331> dislocation decomposes into 1/2<111> and <110> dislocations during deformation at temperatures above 900°C. This decomposition prevents deformation by the 1/2<331> dislocation at temperatures of 1200°C and above. HREM observations of the core of a 1/2<331> dislocation revealed that it was dissociated out of the 13 glide plane after deformation at 900°C, while observations of the core of a 1/2<111> dislocation after deformation at 1100°C revealed that it was dissociated by glide in the 110 plane. These core structures strongly affect the Peierls stress for glide of the 1/2<331> and 1/2<111> dislocations. Large climb dissociations of the 1/2<111> and 1/2<331> dislocations were also observed on the (001) plane, possibly resulting from the precipitation of Si vacancies on dislocations. A detailed comparison of these results with those of Umakoshi, Sakagami, Hirano and Yamane (1990) was undertaken by testing material provided by Umakoshi along (001) at 1000, 1300 and 1400°C and along (771) at 1100°C at a strain rate of 1 × 10-5/s. Marked differences were observed and explained by the dislocation substructure observed after deformation.

Committee:

Arthur Heuer (Advisor)

Keywords:

Dislocations mechanical properties single crystal molybdenum silicide

Thompson, Loren KeithInterfacial studies of molybdenum disulfide semiconductor/electrolyte systems /
Doctor of Philosophy, The Ohio State University, 1983, Graduate School

Committee:

Not Provided (Other)

Subjects:

Chemistry

Keywords:

Molybdenum;Semiconductors;Electrolytes

Eifert, James RichardGravimetric analysis of the austenite/ferrite transformation in iron and iron-molybdenum alloys /
Doctor of Philosophy, The Ohio State University, 1973, Graduate School

Committee:

Not Provided (Other)

Subjects:

Engineering

Keywords:

Chemistry;Iron alloys;Iron-molybdenum alloys

Gardner, Christopher BrentRock-Derived Micronutrient Transport across Landscape Units: Hydrologic Flow Path Analysis and Catchment-Scale Transport in the Tropics and Small Mountainous Rivers
Doctor of Philosophy, The Ohio State University, 2015, Geological Sciences
This dissertation investigates the sources, sinks, and hydrologic transport of molybdenum (Mo) in experimental watersheds in tropical Panama. The role of preferential flow paths during storm events were first investigated using germanium (Ge) and silicon (Si) as flow path tracers to examine the partitioning of precipitation event waters in catchments with different land covers. The riverine concentrations, weathering yields, and fluxes of Mo, vanadium (V), and uranium (U) were investigated in small mountainous rivers and streams draining high standing ocean islands using archived water samples. In Chapter 2 of this dissertation, three end-member water types were identified in three experimental catchments — stream baseflow (high [Si], low Ge/Si ratio), dilute event water (low [Si], moderate Ge/Si ratio), and soil pore water (low [Si], high Ge/Si ratio). A three component mixing model was employed as a hydrograph separation tool. During small rain events, storm flow is dominated by baseflow and dilute event water components. During larger events, the third shallow soil water component with high [Ge] and low [Si] is activated, reaching a maximum during the receding limb of the hydrograph. The magnitude of the increase in [Ge] in storm flow is proportional to the size of precipitation event. This component is interpreted to represent the activation of a continuum of long, preferential flow paths in the shallow soil though which event waters acquire an elevated Ge signal. In Chapter 3, the mixing model from Chapter 2 was applied to the hydrologic cycle of Mo during storm events. Though Mo is considered a rock-derived micronutrient, concentrations were higher in precipitation, canopy throughfall, and shallow soil water than in the groundwater and stream waters in contact with underlying bedrock. A simple mass balance suggests that Mo is being retained within the catchment during storm events. Three and two-component hydrograph separation models consisting of precipitation, soil pore water, and baseflow were applied to predict Mo concentrations in event flow waters resulting from the mixing of these end-members. The modeled fractions vastly over estimated observed Mo concentrations in stormflow, which were modeled better as simple dilution of stream baseflow. Selective chemical soil extractions suggest precipitation-derived Mo is associated with organic material in the soil. Chapter 4 investigates the riverine concentrations, ocean flux, and weathering yields of Mo, V, and U in a large number small mountainous rivers and streams draining high standing ocean islands. Unlike in large river systems, in which Mo is derived predominately from pyrite dissolution, dissolved Mo concentrations in these rivers do not correlate with sulfate. V correlates strongly with Si in terrains dominated by silicate rocks, but not in sedimentary regions. Fluxes of U and Mo into the ocean from igneous terrains are lower than the global average, while fluxes of V from these regions are higher, and up to two orders of magnitude higher in rivers draining young volcanics. Weathering yields of Mo and V in most regions are above the global mean.

Committee:

W. Berry Lyons (Advisor); Anne Carey (Committee Member); Yu-Ping Chin (Committee Member); John Olesik (Committee Member)

Subjects:

Geochemistry; Hydrology

Keywords:

molybdenum; vanadium; uranium; germanium; rivers; hydrograph separation; tropical hydrology; preferential flowpath, small mountainous rivers, coupled biogeochemical cycles

Gross, Carl MorrisGrowth and Characterization of Molybdenum Disulfide Thin Films
Master of Science in Electrical Engineering (MSEE), Wright State University, 2016, Electrical Engineering
Two-dimensional materials, or materials that are only one atomic layer thick, have seen much research in recent years because of their interesting electrical properties. The first of these materials, graphene, was found to have incredible electrical properties but lacked a bandgap in intrinsic films. Without a bandgap, graphene cannot create transistors that can be shut off. Molybdenum disulfide, however, is a two-dimensional semiconductor with a large bandgap. The main issue of molybdenum disulfide is that synthesized films are a much lower quality than their exfoliated counterparts. For molybdenum disulfide to be able to be used practically, a method of synthesis must be found that can reliably create quality large area monolayer films. In this thesis, three methods of molybdenum disulfide film synthesis are presented. Methods implemented used a tube furnace as a chemical vapor deposition system to evaporate source materials to synthesize thin films of molybdenum disulfide. An exploration into the different synthesis parameters shows optimal conditions for these specific methods. Then a discussion of these different methods is presented by judging films grown by using these methods on relevant criteria. This work shows methods to synthesize large area, polycrystalline, small grain, multilayer films, both intrinsic and doped, and to synthesize small area, single crystal and polycrystalline, monolayer films of molybdenum disulfide.

Committee:

Yan Zhuang, Ph.D. (Advisor); Shin Mou, Ph.D. (Committee Member); Michael Saville, Ph.D., P.E. (Committee Member)

Subjects:

Electrical Engineering; Engineering; Materials Science; Nanoscience; Nanotechnology

Keywords:

Molybdenum Disulfide; 2D Materials; Chemical Vapor Deposition; Raman Spectroscopy

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