Browsing by Subject "Ruthenium"
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Item Activity of methanol electro-oxidation at PtRu materials at temperatures in the range of 23°C to 70°C(Texas Tech University, 2004-05) Xu, ShanhongThe electrochemical oxidation of 0.5 M methanol in 0.1 M HCIO4 on catalyst materials comprised of platinum and ruthenium (PtRu) was investigated. Cyclic voltammetry and constant potential amperometry were used to characterize the catalyst materials and study the methanol reaction kinetics. Measurements were performed at temperature in the range of 23°C to 70°C. The following catalyst materials were employed: PtRu black containing 50 at. % Ru supplied by Johnson Matthey of Ward Hill. MA (JM PtRu black); sonochemically prepared nanoparticles of PtRu containing either 50 at. % Ru (SC PtRu(50)) or 25 at. % Ru (SC PtRu(25)); and Pt black (supplied by Johnson Matthey) modified by spontaneous deposition of Ru via either two (JM Pt-Ru(2)) or four deposition cycles (JM Pt-Ru(4)). The rate of methanol oxidation was assessed through constant potential amperometry measurements. Current was recorded 20 min after stepping to the reaction potential. Mechanistic information was derived from Tafel plots (plot of the logarithm of the current versus the reaction potential).Item Controlling nucleation and growth of ultra-thin ruthenium films in chemical vapor deposition(2016-05) Liao, Wen; Ekerdt, John G.; Korgel, Brian A; Hwang, Gyeong S; Hildebrandt Ruiz, Lea; Ferreira, PauloAs feature sizes in microelectronic devices decrease, ultra-thin (< 3 nm) and smooth diffusion barriers are required to prevent copper from diffusing into the surrounding dielectric layers and to limit electron scattering at the copper-liner surface. Chemical vapor deposition (CVD) is one route to these barriers. The inhibitor gas adsorbs on metal nanoparticles, forces additional nucleation and enhances nucleation density. Island growth combined with a sparse nucleation density leads to film roughness and the deposition of more metal mass than is needed to form a film of sufficient thickness to function as a copper diffusion barrier when compared to a uniformly-thick metal film. In the first study, a higher nucleation density and smoother Ru film is achieved in CVD with CO addition during growth. CO competes with Ru3(CO)12 for free hydroxyl adsorption. The CO addition to Ru3(CO)12 deposition at proper timing and effective partial pressure reduces the film growth rate, surface roughness and nanocrystalline grain size by chemical vapor deposition. The second study reports the use of ammonia to inhibit the growth of previously-nucleated ruthenium islands and force the nucleation of additional islands such that thinner films form as the islands coalesce with continued growth using Ru3(CO)12. The ammonia addition reduces the film nanocrystallinity and the films appear X-ray amorphous with the highest ammonia partial pressure during film deposition. In the third study, films grown from Ru(tBu-Me-amd)2(CO)2 form a 2D wetting layer before 3D particle growth is observed. CO and ammonia addition to the gas phase during film growth from Ru(tBu-Me-amd)2(CO)2 leads to smoother films by inducing surface reconstructions during the film growth; these gases also lead to films with lower resistivity and lower crystalline character. Overall, this research is to understand how blocking adsorbed moieties effect the nucleation of metals on a silica substrate, and to discover the principles leading to ultra-thin and smooth metallic films in CVD.Item Deposition and properties of Co- and Ru-based ultra-thin films(2009-12) Henderson, Lucas Benjamin; Ekerdt, John G.Future copper interconnect systems will require replacement of the materials that currently comprise both the liner layer(s) and the capping layer. Ruthenium has previously been considered as a material that could function as a single material liner, however its poor ability to prevent copper diffusion makes it incompatible with liner requirements. A recently described chemical vapor deposition route to amorphous ruthenium-phosphorus alloy films could correct this problem by eliminating the grain boundaries found in pure ruthenium films. Bias-temperature stressing of capacitor structures using 5 nm ruthenium-phosphorus film as a barrier to copper diffusion and analysis of the times-to-failure at accelerated temperature and field conditions implies that ruthenium-phosphorus performs acceptably as a diffusion barrier for temperatures above 165 °C. The future problems associated with the copper capping layer are primarily due to the poor adhesion between copper and the current Si-based capping layers. Cobalt, which adheres well to copper, has been widely proposed to replace the Si-based materials, but its ability to prevent copper diffusion must be improved if it is to be successfully implemented in the interconnect. Using a dual-source chemistry of dicobaltoctacarbonyl and trimethylphosphine at temperatures from 250-350 °C, amorphous cobalt-phosphorus can be deposited by chemical vapor deposition. The films contain elemental cobalt and phosphorus, plus some carbon impurity, which is incorporated in the film as both graphitic and carbidic (bonded to cobalt) carbon. When deposited on copper, the adhesion between the two materials remains strong despite the presence of phosphorus and carbon at the interface, but the selectivity for growth on copper compared to silicon dioxide is poor and must be improved prior to consideration for application in interconnect systems. A single molecule precursor containing both cobalt and phosphorus atoms, tetrakis(trimethylphosphine)cobalt(0), yields cobalt-phosphorus films without any co-reactant. However, the molecule does not contain sufficient amounts of amorphizing agents to fully eliminate grain boundaries, and the resulting film is nanocrystalline.Item Design and analysis of precursors for CVD of Ru thin films and Li-ion batteries with MoP₄ anode materials(2013-08) De Pue, Lauren Joy; Jones, Richard A., 1954-The chemical vapor deposition growth of amorphous metallic alloys is currently of interest for potential uses in electronic devices. We have explored the use of ligands having Ru-H, Ru-N, and Ru-P bonds to study the effects of ligand selection. The synthesis and design of novel Ru dinuclear complexes using volatile ligands such as 3,5-bis-trifluoromethylpyrazolate and trimethylphosphine will be presented as well as materials characterization studies on grown films. Another class of functional materials of interest is the transition metal phosphides (TMPs) which have found applications in Li-ion batteries. Current research on TMPs is focused on obtaining materials with improved or new compositions and morphologies and on improving Li insertion/de-insertion reactions and charge carrying capacities. Traditional routes to these materials involve the use of high temperatures and pressures. The work presented here will focus on a synthetic route which employs relatively mild conditions. Surface analysis studies and the electrochemical performance of mesoporous MoP₄ for use as anode materials in Li-ion batteries will be described.Item Development of ruthenium catalyzed hydrogenative carbonyl addition reactions(2014-05) McInturff, Emma Leigh; Krische, Michael J.Metal-catalyzed, hydrogenative methods for carbon-carbon bond formation are attractive alternatives to traditional carbonyl addition reactions. Through in situ generation of aldehyde and organometallic species, these redox-triggered reactions circumvent the need for preactivation of reactive partners, thereby providing a more atom economic, efficient approach to carbonyl addition products. Efforts have been focused on the development of ruthenium-catalyzed coupling reactions of primary and secondary alcohols to basic feedstock chemicals and easily accessible and stable unsaturated compounds. To perform highly stereoselective reactions, investigation into the factors that control stereoselectivity in ruthenium catalyzed transfer hydrogenative couplings was undertaken. As a critical tool for the construction of organic molecules, modernizing methods for carbonyl addition can contribute to the evolution of synthetic organic methodology.Item Electrochemisty and electrogenerated chemiluminescence of Ru(phen)₂dppz(BF₄)₂ both free and intercalated into DNA(2007) Calhoun, Robert Lee; Bard, Allen J.Ruthenium (II) bisphenanthroline dipyridophenazine, Ru(phen)2dppz2+, exhibits first oxidation and reduction voltammetric responses which correlate well with the UVvis spectroscopy and are typical to the compound class. The complex proves energy sufficient for electrogenerated chemiluminescence (ECL), and does so in aqueous media with co-reactants, also similar to its phenanthroline and bipyridine analogues. However, this behavior is curious since this compound’s aqueous photoluminescence (PL) is undetectable but exhibits ‘light switch’ behavior upon intercalation into both calf thymus DNA and other polynucleotides in that the PL greatly increases. The ECL of both the free and intercalated complex is presented as well as scanning electrochemical microscopy (SECM) studies to understand the complex’s kinetic behavior in water upon oxidation. In an effort to understand the SECM results, the program COMSOL Multiphysics is used to model the EC’ (catalytic) following reaction. The simulation results are validated using the ferrocyanide/cysteine system, which is known to exhibit the EC’ mechanism.Item Electrochemisty and electrogenerated chemiluminescence of Ru(phen)₂dppz(BF₄)₂ both free and intercalated into DNA(2007-05) Calhoun, Robert Lee; Bard, Allen J.Item Part 1: Isolation of Orexin Receptor Regulators via a Microarray-Based,Two-Color Cell Binding Screen. Part II: Targeted Inactivation of Proteins triggered by Visible Light.(2009-09-04) Lee, Jiyong; Kodadek, ThomasPart I. Isolation of orexin receptor regulators via a microarray-based, two-color, cell-binding screen. We have developed a novel two-color, cell-binding peptoid microarray screening approach with which we discovered new orexin receptor ligands. We found that peptoids on microarray, which showed preferential binding to receptor-expressing cells, indeed regulate the function of the receptor in living cells. Although cell-adhesion peptide microarrays have been used to isolate peptides that bind to cell surface receptors, this is the first time that a non-peptide, small molecule microarray has been used to do so. We also demonstrated that the pharmacophore of a hit peptoid can be rapidly identified through sarcosine scanning. Subsequent modifications of the pharmacophore yielded a potent antagonist (IC50 = 1.7 ? and an allosteric potentiator (EC50 = 120 nM) of the orexin receptor. Part II. Targeted Inactivation of Proteins Triggered by Visible Light Advances in genomics and proteomics have helped to provide thousands of potential drug targets and thus target validation strategies are more important than ever. Among target validation technologies, we are interested in chromophore-assisted light inactivation of proteins (CALI) since it allows for time-resolved protein knock-out in living cells. However, the practical use of this technology is limited, partially because of the low CALI efficiency of chromophores that are currently in use. To solve this problem, we developed a convenient system to compare different chromophores for their CALI efficiency, from which we found that Ru(II) complex is a photo-stable and unusually efficient CALI ?rhead?This finding led us to develop photo-chemical protein knock-out reagents?n which Ru(II) complex was conjugated to small molecule ligands targeting VEGFR2 or the 26S proteasome. When irradiated with visible light, these reagents showed significantly increased potencies in inhibiting VEGF-induced VEGFR2 activation or proteolytic activity of the 26S proteasome.Item Transition metal catalyzed carbonyl additions under the conditions of transfer hydrogenation(2011-05) Patman, Ryan Lloyd; Krische, Michael J.; Anslyn, Eric V.; Siegel, Dionicio R.; Brodbelt, Jennifer S.; Kerwin, Sean M.The efficient construction of complex organic molecules mandates that an assortment of methods for forming C-C bonds be available to the practicing synthetic chemist. The addition of carbon based nucleophiles to carbonyl compounds represents a broad class of reactions used to achieve this goal. Traditional methodology requires the use of stoichiometrically preformed organometallic reagents as nucleophiles in this type of reaction. However, due to the moisture sensitivity, excessive preactivation and inevitable generation of stoichiometric waste required for the use of these reagents, alternative methods have become a focus of the synthetic organic community. The research presented in this dissertation describes a new class of C-C bond forming reactions enabled through catalytic transfer hydrogenation. Here, the development and implementation of efficient green methods for carbonyl addition employing π-unsaturates as surrogates to preformed organometallic reagents is described. Additionally, this research describes the first systematic studies toward using alcohols as electrophiles in carbonyl allylation, propargylation and vinylation reactions.Item Transition metal catalyzed regioselective carbon-carbon bond formation mediated by transfer hydrogenation(2015-05) Sam, Brannon; Krische, Michael J.; Anslyn, Eric V; Dong, Guangbin; Keatinge-Clay, Adrian T; Kerwin, Sean MOne of the more formidable challenges in the synthesis of complex organic molecules remains the efficient formation of carbon-carbon bonds. The development of a broad class of reactions to achieve this goal involves the addition of carbon based nucleophiles to carbonyl and imine compounds. Until recently, classical approaches to carbon-carbon bond formation generally required the use of stoichiometric pre-formed organometallic reagents to serve as nucleophiles, which translate into stoichiometric organometallic byproducts. In an effort to minimize nucleophile pre-activation and byproduct formation, our lab has developed efficient methods for carbonyl and imine additions via in situ formation of alkyl metal nucleophiles from π-unsaturates. The research reported herein describes our advances in an assortment of transition metal-catalyzed carbon-carbon bond forming reactions mediated by transfer hydrogenation, including regioselective hydrohydroxymethylation, hydrohydroxyfluoroalkylation, and hydroaminomethylation. Additionally, the investigation of regioselective carbonyl vinylation is reported.Item Transition metal-catalyzed carbon-carbon bond formation utilizing transfer hydrogenation(2015-05) Montgomery, Timothy Patrick; Krische, Michael J.; Anslyn, Eric V; Dong, Guangbon; Brodbelt, Jennifer S; Liu, Hung-wenA central tenant of organic synthesis is the construction of carbon-carbon bonds. One of the traditional methods for carrying out such transformations is that of carbonyl addition. Unfortunately, traditional carbonyl addition chemistry suffers various drawbacks: preactivation, moisture sensitivity, and the generation of stoichiometric organometallic waste. The research presented in this dissertation focuses on the development of methods that make use of nucleophile-electrophile pairs generated in situ via transfer hydrogenation, which allow the formation of carbonyl or imine addition products from the alcohol or amine oxidation level; streamlining the construction of complex molecules from simple, readily available starting materials. Additionally, studies toward the total synthesis of the fibrinogen receptor inhibitor tetrafibricin, utilizing the methods developed in catalytic carbon-carbon bond formation through the addition, transfer or removal of hydrogen, are presented.