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Electrochemical Synthesis and Applications of Layered Double Hydroxides and Derivatives

Description: Layered double hydroxides (LDH) are a class of anionic clay with alternating layers of positive and negative charge. A metal hydroxide layer with divalent and trivalent metals with a positive charge is complemented by an interlayer region containing anions and water with a negative charge. The anions can be exchanged under favorable conditions. Hydrotalcite (Mg6Al2(OH)16[CO3]·4H2O) and other variations are naturally occurring minerals. Synthetic LDH can be prepared as a powder or film by numerous methods. Synthetic LDH is used in electrode materials, adsorbents, nuclear waste treatment, drug delivery systems, water treatment, corrosion protection coatings, and catalysis. In this dissertation Zn-Al-NO3 derivatives of zaccagnaite (Zn4Al2(OH)12[CO3]·3H2O) are electrochemically synthesized as films and applied to sensing and corrosion resistance applications. First, Zn-Al-NO3 LDH was potentiostatically electrosynthesized on glassy carbon substrates and applied to the electrochemical detection of gallic acid and caffeic acid in aqueous solutions. The modified electrode was then applied to the detection of gallic acid in green tea samples. The focus of the work shifts to corrosion protection of stainless steel. Modified zaccagnaite films were electrodeposited onto stainless steel in multiples layers to reduce defects caused by drying of the films. The films were deposited using a step potential method. The corrosion resistance of the films in a marine environment was investigated while immersed in 3.5 wt.% NaCl environments. Next modified zaccagnaite films were potentiostatically electrodeposited onto stainless steel followed by a hydrophobization reaction with palmitic acid in order to prepare superhydrophobic (>150° contact angle) surfaces. Each parameter of the film synthesis was optimized to produce a surface with the highest possible contact angle. The fifth chapter examines the corrosion resistance of the optimized superhydrophobic film and a hydrophobic film. The hydrophobic film is prepared using the same procedure as the superhydrophobic film except for a difference in electrodeposition potential. The ...
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Date: August 2015
Creator: Kahl, Michael S.
Partner: UNT Libraries

Novel Carborane Derived Semiconducting Thin Films for Neutron Detection and Device Applications

Description: Novel carborane (B10C2H12) and aromatic compounds (benzene, pyridine, diaminobenzene) copolymers and composite materials have been fabricated by electron beam induced cross-linking and plasma enhanced chemical vapor deposition (PECVD) respectively. Chemical and electronic structure of these materials were studied using X-ray and ultra-violet photoelectron spectroscopy (XPS and UPS). UPS suggest that the systematic tuning of electronic structure can be achieved by using different aromatic compounds as co-precursors during the deposition. Furthermore, top of valence band is composed of states from the aromatic moieties implying that states near bottom of the conduction band is derived from carborane moieties. Current- voltage (I-V) measurements on the ebeam derived B10C2HX: Diaminobenzene films suggest that these films exhibit enhanced electron hole separation life time. Enhanced electron hole separation and charge transport are critical parameters in designing better neutron voltaic devices. Recently, PECVD composite films of ortho-carborane and pyridine exhibited enhanced neutron detection efficiency even under zero bias compared to the pure ortho-carborane derived films. This enhancement is most likely due to longer electron-hole separation, better charge transport or a combination of both. The studies determining the main factors for the observed enhanced neutron detection are in progress by fabricating composite films of carborane with other aromatic precursors and by altering the plasma deposition conditions. This research will facilitate the development of highly sensitive and cost effective neutron detectors, and has potential applications in spintronics and photo-catalysis.
Date: August 2015
Creator: James, Robinson
Partner: UNT Libraries

Interfacial Electrochemistry of Copper and Spectro-Electrochemical Characterization of Oxygen Reduction Reaction

Description: The first part of this dissertation highlights the contents of the electrochemical characterization of Cu and its electroplating on Ru-based substrates. The growth of Ru native oxide does diminish the efficiency of Cu plating on Ru surface. However, the electrochemical formed irreversible Ru hydrate dioxide (RuOxHy) shows better coverage of Cu UPD. The conductive Ru oxides are directly plateable liner materials as potential diffusion barriers for the IC fabrication. The part II of this dissertation demonstrates the development of a new rapid corrosion screening methodology for effective characterization Cu bimetallic corrosion in CMP and post-CMP environments. The corrosion inhibitors and antioxidants were studied in this dissertation. In part III, a new SEC methodology was developed to study the ORR catalysts. This novel SEC cell can offer cheap, rapid optical screening results, which helps the efficient development of a better ORR catalyst. Also, the SEC method is capable for identifying the poisoning of electrocatalysts. Our data show that the RuOxHy processes several outstanding properties of ORR such as high tolerance of sulfation, high kinetic current limitation and low percentage of hydrogen peroxide.
Date: August 2011
Creator: Yu, Kyle Kai-Hung
Partner: UNT Libraries

Molecular Structure Analyses of Asymmetric Hydrocarbon Liquid Compounds in the Gas Phase Using Chirped-pulse Fourier Transform Microwave Spectroscopy: Acyl Chlorides and Perfluorinated Acyl Chlorides

Description: Examinations of the effects of (a.) alkyl carbon chain length and (b.) perfluorination of acyl chlorides; propionyl chloride, butyryl chloride, valeroyl chloride, and perfluorinated acyl chlorides; perfluoropropionyl chloride and perfluorobutyryl chloride, are reported and compared using CP-FTMW spectroscopy. All of these molecules are already published in various journals except for valeroyl chloride. The chapters are organized by molecule alkyl chain length and include some background theory. Conformational stability, internal rotation, helicity, and ionic character of the C-Cl bond via the nuclear electric quadrupole coupling constant (χzz) are analyzed. Results show syn, syn-anti/syn-gauche, and syn-anti-anti/syn-gauche-anti stable conformations. Internal rotation was only seen in propionyl chloride. Helicity was not observed. (χzz) was observed to be inert to alkyl chain length, ~ 60 MHz and ~ 65 MHz for the nonfluorinated and fluorinated acyl chlorides. Partial fluorination and varying functional groups are recommended.
Date: August 2011
Creator: Powoski, Robert A.
Partner: UNT Libraries

The Effect of Plasma on Silicon Nitride, Oxynitride and Other Metals for Enhanced Epoxy Adhesion for Packaging Applications

Description: The effects of direct plasma chemistries on carbon removal from silicon nitride (SiNx) and oxynitride (SiOxNy ) surfaces and Cu have been studied by x-photoelectron spectroscopy (XPS) and ex-situ contact angle measurements. The data indicate that O2,NH3 and He capacitively coupled plasmas are effective at removing adventitious carbon from silicon nitride (SiNx) and Silicon oxynitride (SiOxNy ) surfaces. O2plasma and He plasma treatment results in the formation of silica overlayer. In contrast, the exposure to NH3 plasma results in negligible additional oxidation of the SiNx and SiOxNy surface. Ex-situ contact angle measurements show that SiNx and SiOxNy surfaces when exposed to oxygen plasma are initially more hydrophilic than surfaces exposed to NH3 plasma and He plasma, indicating that the O2 plasma-induced SiO2 overlayer is highly reactive towards ambient corresponding to increased roughness measured by AFM. At longer ambient exposures (>~10 hours), however surfaces treated by either O2, He or NH3 plasma exhibit similar steady state contact angles, correlated with rapid uptake of adventitious carbon, as determined by XPS. Surface passivation by exposure to molecular hydrogen prior to ambient exposure significantly retards the increase in the contact angle upon the exposure to ambient. The results suggest a practical route to enhancing the time available for effective bonding to surfaces in microelectronics packaging applications.
Date: August 2014
Creator: Gaddam, Sneha Sen
Partner: UNT Libraries

Electrodeposition of Nickel and Nickel Alloy Coatings with Layered Silicates for Enhanced Corrosion Resistance and Mechanical Properties

Description: The new nickel/layered silicate nanocomposites were electrodeposited from different pHs to study the influence on the metal ions/layered silicate plating solution and on the properties of the deposited films. Nickel/layered silicate nanocomposites were fabricated from citrate bath atacidic pHs (1.6−3.0), from Watts’ type solution (pH ~4-5), and from citrate bath at basic pH (~9). Additionally, the new nickel/molybdenum/layered silicate nanocomposites were electrodeposited from citrate bath at pH 9.5. The silicate, montmorillonite (MMT), was exfoliated by stirring in aqueous solution over 24 hours. The plating solutions were analyzed for zeta potential, particle size, viscosity, and conductivity to investigate the effects of the composition at various pHs. The preferred crystalline orientation and the crystalline size of nickel, nickel/layered silicate, nickel/molybdenum, and nickel/molybdenum/layered silicate films were examined by X-ray diffraction. The microstructure of the coatings and the surface roughness was investigated by scanning electron microscopy and atomic force microscopy. Nickel/molybdenum/layered silicate nanocomposites containing low content of layered silicate (1.0 g/L) had increase 32 % hardness and 22 % Young’s modulus values over the pure nickel/molybdenum alloy films. The potentiodynamic polarization and electrochemical impedance measurements showed that the nickel/molybdenum/layered silicate nanocomposite layers have higher corrosion resistance in 3.5% NaCl compared to the pure alloy films. The corrosion current density of the nickel/molybdenum/layered silicate nanocomposite composed of 0.5 g/L MMT is 0.63 µA·cm-2 as compare to a nickel/molybdenum alloy which is 2.00 µA·cm-2.
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Date: August 2014
Creator: Tientong, Jeerapan
Partner: UNT Libraries

Development of Novel Semi-conducting Ortho-carborane Based Polymer Films: Enhanced Electronic and Chemical Properties

Description: A novel class of semi-conducting ortho-carborane (B10C2H12) based polymer films with enhanced electronic and chemical properties has been developed. The novel films are formed from electron-beam cross-linking of condensed B10C2H12 and B10C2H12 co-condensed with aromatic linking units (Y) (Y=1,4-diaminobenzene (DAB), benzene (BNZ) and pyridine (PY)) at 110 K. The bonding and electronic properties of the novel films were investigated using X-ray photoelectron spectroscopy (XPS), UV photoelectron spectroscopy (UPS) and Mulliken charge analysis using density functional theory (DFT). These films exhibit site-specific cross-linking with bonding, in the pure B10C2HX films, occurring at B sites non-adjacent to C in the B10C2H12 icosahedra. The B10C2H12:Y films exhibit the same phenomena, with cross-linking that creates bonds primarily between B sites non-adjacent to C in the B10C2H12 icosahedra to C sites in the Y linking units. These novel B10C2HX: Y linked films exhibit significantly different electron structure when compared to pure B10C2HX films as seen in the UPS spectra. The valence band maxima (VBM) shift from - 4.3 eV below the Fermi level for pure B10C2HX to -2.6, -2.2, and -1.7 for B10C2HX:BNZ, B10C2HX:PY, and B10C2HX:DAB, respectively. The top of the valence band is composed of states derived primarily from the Y linking units, suggesting that the bottom of the conduction band is composed of states primarily from B10C2H12. Consequently these B10C2HX:Y films may exhibit longer electron-hole separation lifetimes as compared to pure B10C2HX films. This research should lead to an enhancement of boron carbide based neutron detectors, and is of potential significance for microelectronics, spintronics and photo-catalysis.
Date: August 2013
Creator: Pasquale, Frank L.
Partner: UNT Libraries

Design and Development of Soft Landing Ion Mobility: A Novel Instrument for Preparative Material Development

Description: The design and fabrication of a novel soft landing instrument Soft Landing Ion Mobility (SLIM) is described here. Topics covered include history of soft landing, gas phase mobility theory, the design and fabrication of SLIM, as well as applications pertaining to soft landing. Principle applications devised for this instrument involved the gas phase separation and selection of an ionized component from a multicomponent gas phase mixture as combing technique to optimize coatings, catalyst, and a variety of alternative application in the sciences.
Date: August 2011
Creator: Davila, Stephen Juan
Partner: UNT Libraries

Cu Electrodeposition on Ru-Ta and Corrosion of Plasma Treated Cu in Post Etch Cleaning Solution

Description: In this work, the possibility of Cu electrodeposition on Ru-Ta alloy thin films is explored. Ru and Ta were sputter deposited on Si substrate with different composition verified by RBS. Four point probe, XRD, TEM and AFM were used to study the properties of Ru-Ta thin films such as sheet resistance, crystallinity, grain size, etc. Cyclic voltammetry is used to study the Cu electrodeposition characteristics on Ru-Ta after various surface pretreatments. The results provide insights on the removal of Ta oxide such that it enables better Cu nucleation and adhesion. Bimetallic corrosion of Cu on modified Ru-Ta surface was studied in CMP related chemicals. In Cu interconnect fabrication process, the making of trenches and vias on low-k dielectric films involves the application of fluorocarbon plasma etch gases. Cu microdots deposited on Ru and Ta substrate were treated by fluorocarbon plasma etch gases such as CF4, CF4+O2, CH2F2, C4F8 and SF6 and investigated by using x-ray photoelectron spectroscopy, contact angle measurement and electrochemical techniques. Micropattern corrosion screening technique was used to measure the corrosion rate of plasma treated Cu. XPS results revealed different surface chemistry on Cu after treating with plasma etching. The fluorine/carbon ratio of the etching gases results in different extent of fluorocarbon polymer residues and affects the cleaning efficiency and Cu corrosion trends.
Date: August 2011
Creator: Sundararaju Meenakshiah Pillai, Karthikeyan
Partner: UNT Libraries

Boron Nitride by Atomic Layer Deposition: A Template for Graphene Growth

Description: The growth of single and multilayer BN films on several substrates was investigated. A typical atomic layer deposition (ALD) process was demonstrated on Si(111) substrate with a growth rate of 1.1 Å/cycle which showed good agreement with the literature value and a near stoichiometric B/N ratio. Boron nitride films were also deposited by ALD on Cu poly crystal and Cu(111) single crystal substrates for the first time, and a growth rate of ~1ML/ALD cycle was obtained with a B/N ratio of ~2. The realization of a h-BN/Cu heterojunction was the first step towards a graphene/h-BN/Cu structure which has potential application in gateable interconnects.
Date: August 2011
Creator: Zhou, Mi
Partner: UNT Libraries