UNT Theses and Dissertations - 84 Matching Results

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Design Considerations and Implementation of Portable Mass Spectrometers for Environmental Applications: Portable mass spectrometers provide a unique opportunity to obtain in situ measurements. This minimizes need for sample collection or in laboratory analysis. Membrane Inlet Mass Spectrometry (MIMS) utilizing a semi permeable membrane for selective rapid introduction for analysis. Polydimethylsiloxane membranes have been proven to be robust in selecting for aromatic chemistries. Advances in front end design have allowed for increased sensitivity, rapid sample analysis, and on line measurements. Applications of the membrane inlet technique have been applied to environmental detection of clandestine drug chemistries and pollutants. Emplacement of a mass spectrometer unit in a vehicle has allowed for large areas to be mapped, obtaining a rapid snapshot of the various concentrations and types of environmental pollutants present. Further refinements and miniaturization have allowed for a backpackable system for analysis in remote harsh environments. Inclusion of atmospheric dispersion modeling has yielded an analytical method of approximating upwind source locations, which has law enforcement, military, and environmental applications. The atmospheric dispersion theories have further been applied to an earth based separation, whereby chemical properties are used to approximate atmospheric mobility, and chemistries are further identified has a portable mass spectrometer is traversed closer to a point source.
Characterization of Aprotic Solutes and Solvents Using Abraham Model Correlations: Experimental data were obtained for the computation of mole fraction solubilities of three dichloronitrobenzenes in organic solvents at 25oC, and solubility ratios were obtained from this data. Abraham model equations were developed for solutes in tributyl phosphate that describe experimental values to within 0.15 log units, and correlations were made to describe solute partitioning in systems that contain either "wet" or "dry" tributyl phosphate. Abraham model correlations have also been developed for solute transfer into anhydrous diisopropyl ether, and these correlations fit in well with those for other ethers. Abraham correlations for the solvation of enthalpy have been derived from experimental and literature data for mesitylene, p-xylene, chlorobenzene, and 1,2-dichlorobenzene at 298.15 K. In addition, the enthalpy contribution of hydrogen bonding between these solutes and acidic solvents were predicted by these correlations and were in agreement with an established method. Residual plots corresponding to Abraham models developed in all of these studies were analyzed for trends in error between experimental and calculated values.
Chemical and Electronic Structure of Aromatic/Carborane Composite Films by PECVD for Neutron Detection: Boron carbide-aromatic composites, formed by plasma-enhanced co-deposition of carboranes and aromatic precursors, present enhanced electron-hole separation as neutron detector. This is achieved by aromatic coordination to the carborane icosahedra and results in improved neutron detection efficiency. Photoemission (XPS) and FTIR suggest that chemical bonding between B atoms in icosahedra and aromatic contents with preservation of π system during plasma process. XPS, UPS, density functional theory (DFT) calculations, and variable angle spectroscopic ellipsometery (VASE) demonstrate that for orthocarborane/pyridine and orthocarborane/aniline films, states near the valence band maximum are aromatic in character, while states near the conduction band minimum include those of either carborane or aromatic character. Thus, excitation across the band gap results in electrons and holes on carboranes and aromatics, respectively. Further such aromatic-carborane interaction dramatically shrinks the indirect band gap from 3 eV (PECVD orthocarborane) to ~ 1.6 eV (PECVD orthocarborane/pyridine) to ~1.0 eV (PECVD orthocarborane/aniline), with little variation in such properties with aromatic/orthocarborane stoichiometry. The narrowed band gap indicate the potential for greatly enhanced charge generation relative to PECVD orthocarborane films, as confirmed by zero-bias neutron voltaic studies. The results indicate that the enhanced electron-hole separation and band gap narrowing observed for aromatic/orthocarborane films relative to PECVD orthocarborane, has significant potential for a range of applications, including neutron detection, photovoltaics, and photocatalysis. Acknowledgements: This work was supported by the Defense Threat Reduction Agency (Grant No.HDTRA1-14-1-0041). James Hilfiker is also gratefully acknowledged for stimulating discussions.
Analysis of Trace Amounts of Adulterants Found in Powders/Supplements Utilizing Direct Inject, Nanomanipulation, and Mass Spectrometry: The regulations of many food products in the United States have been made and followed very well but unfortunately some products are not put under such rigorous standards as others. This leads to products being sold, that are thought to be healthy, but in reality contain unknown ingredients that may be hazardous to the consumers. With the use of several instrumentations and techniques the detection, characterization and identification of these unknown contaminates can be determined. Both the AZ-100 and the TE2000 inverted microscope were used for visual characterizations, image collection and to help guide the extraction. Direct analyte-probed nanoextraction (DAPNe) technique and nanospray ionization mass spectrometry (NSI-MS) was the technique used for examination and identification of all adulterants. A Raman imaging technique was than introduced and has proven to be a rapid, non-destructive and distinctive way to localize a specific adulterant. By compiling these techniques then applying them to the FDA supplied test samples three major adulterants were detected and identified.
Direct Atomic Level Controlled Growth and Characterization of h-BN and Graphene Heterostructures on Magnetic Substrates for Spintronic Applications: Epitaxial multilayer h-BN(0001) heterostructures and graphene/h-BN heterostructures have many potential applications in spintronics. The use of h-BN and graphene require atomically precise control and azimuthal alignment of the individual layers in the structure. These in turn require fabrication of devices by direct scalable methods rather than physical transfer of BN and graphene flakes, and such scalable methods are also critical for industrially compatible development of 2D devices. The growth of h-BN(0001) multilayers on Co and Ni, and graphene/h-BN(0001) heterostructures on Co have been studied which meet these criteria. Atomic Layer Epitaxy (ALE) of BN was carried out resulting in the formation of macroscopically continuous h-BN(0001) multilayers using BCl3 and NH3 as precursors. X-ray photoemission spectra (XPS) show that the films are stoichiometric with an average film thickness linearly proportional to the number of BCl3/NH3 cycles. Molecular beam epitaxy (MBE) of C yielded few layer graphene in azimuthal registry with BN/Co(0001) substrate. Low energy electron diffraction (LEED) measurements indicate azimuthally oriented growth of both BN and graphene layers in registry with the substrate lattice. Photoemission data indicate B:N atomic ratios of 1:1. Direct growth temperatures of 600 K for BN and 800 to 900 K for graphene MBE indicate multiple integration schemes for applications in spintronics.
Characterization of Post-Plasma Etch Residues and Plasma Induced Damage Evaluation on Patterned Porous Low-K Dielectrics Using MIR-IR Spectroscopy: As the miniaturization of functional devices in integrated circuit (IC) continues to scale down to sub-nanometer size, the process complexity increases and makes materials characterization difficult. One of our research effort demonstrates the development and application of novel Multiple Internal Reflection Infrared Spectroscopy (MIR-IR) as a sensitive (sub-5 nm) metrology tool to provide precise chemical bonding information that can effectively guide through the development of more efficient process control. In this work, we investigated the chemical bonding structure of thin fluorocarbon polymer films deposited on low-k dielectric nanostructures, using Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). Complemented by functional group specific chemical derivatization reactions, fluorocarbon film was established to contain fluorinated alkenes and carbonyl moieties embedded in a highly cross-linked, branched fluorocarbon structure and a model bonding structure was proposed for the first time. In addition, plasma induced damage to high aspect ratio trench low-k structures especially on the trench sidewalls was evaluated both qualitatively and quantitatively. Damage from different plasma processing was correlated with Si-OH formation and breakage of Si-CH3 bonds with increase in C=O functionality. In another endeavor, TiN hard mask defect formation after fluorocarbon plasma etch was characterized and investigated. Finding suggest the presence of water soluble amines that could possibly trigger the formation of TiN surface defect. An effective post etch treatment (PET) methods were applied for etch residue defect removal/suppression.
Direct Inject Mass Spectrometry for Illicit Chemistry Detection and Characterization: The field of direct inject mass spectrometry includes a massive host of ambient ionization techniques that are especially useful for forensic analysts. Whether the sample is trace amounts of drugs or explosives or bulk amounts of synthetic drugs from a clandestine laboratory, the analysis of forensic evidence requires minimal sample preparation, evidence preservation, and high sensitivity. Direct inject mass spectrometry techniques can rarely provide all of these. Direct analyte-probed nanoextraction coupled to nanospray ionization mass spectrometry, however, is certainly capable of achieving these goals. As a multifaceted tool developed in the Verbeck laboratory, many forensic applications have since been investigated (trace drug and explosives analysis). Direct inject mass spectrometry can also be easily coupled to assays to obtain additional information about the analytes in question. By performing a parallel artificial membrane assay or a cell membrane stationary phase extraction prior to direct infusion of the sample, membrane permeability data and receptor activity data can be obtained in addition to the mass spectral data that was already being collected. This is particularly useful for characterizing illicit drugs and their analogues for a biologically relevant way to schedule new psychoactive substances.
Electrodeposited Metal Matrix Composites for Enhanced Corrosion Protection and Mechanical Properties: In the oil and gas industry, high corrosion resistance and hardness are needed to extend the lifetime of the coatings due to exposure to high stress and salt environments. Electrodeposition has become a favorable technique in synthesizing coatings because of low cost, convenience, and the ability to work at low temperatures. Electrodeposition of metal matrix composites has become popular for enhanced corrosion resistance and hardness in the oil and gas industry because of the major problems that persist with corrosion. Two major alloys of copper-nickel, 90-10 and 70-30, were evaluated for microbial corrosion protection in marine environments on a stainless steel substrate. Copper and copper alloys are commonly used in marine environments to resist biofouling of materials by inhibiting microbial growth. Literature surveying the electrodeposition of Cu-Ni incorporated with nano- to micro- particles to produce metal matrix composites has been reviewed. Also, a novel flow cell design for the enhanced deposition of metal matrix composites was examined to obtain the optimal oriented structure of the layered silicates in the metal matrix. With the addition of montmorillonite into the Ni and Cu-Ni matrix, an increase in strength, adhesion, wear and fracture toughness of the coating occurs, which leads to an increase corrosion resistance and longevity of the coating. These coatings were evaluated for composition and corrosion using many different types of instrumental and electrochemical techniques. The overall corrosion resistance and mechanical properties were improved with the composite films in comparison to the pure metals, which proves to be advantageous for many economic sectors including the oil and gas industry.
Forensic Analysis of Ink on Documents Using Direct Analyte-Probed Nanoextraction Coupled Techniques: Analzying questioned documents in a nondestructive nature has been an issue for the forensic science community. Using nondestructive techniques such as video spectral comparator does not give reliable information due to the variations in gray or color levels that are distinguished differently by analysts. Destructive techniques such as chromatography give dependable, qualitative and quantitative, information but involves altering the evidentiary value of these questioned documents. The paradox of document examination becomes a problem when document evidence is involved, especially when trying to preserve its evidentiary value and critical data is needed. Thus, a nondestructive technique has been developed to solve the loopholes in document examinations. Direct analyte-probed nanoextraction (DAPNe) is a nanomanipulation technique that extracts ink directly off the document for further examination. A watermark is left, at most, post-extraction. DAPNe utilizes a tip emitter, pre-filled with a solvent, which is controlled in x-, y-, and z-coordinates via joystick controller and aspirates/extracts using a pressure injector. The versatility of this technique lies within the solvent chemistry and its capability to be coupled to various types of instrumentation. The extraction solvent can be altered to target specific components in the ink. For example, a chelator may be added to target metal ions found in ancient inks or methanol may be added to target certain organic resins and binding agents found in modern inks. In this study, DAPNe has been coupled to nanospray ionization mass spectrometry, fluorescence microscopy, Raman spectroscopy, matrix-assisted laser desorption ionization mass spectrometry, and laser ablation to solve questioned document concerns in the area of falsified or forged documents, redacted documents, and aging studies.
Interfacial Electrochemistry of Cu/Al Alloys for IC Packaging and Chemical Bonding Characterization of Boron Doped Hydrogenated Amorphous Silicon Films for Infrared Cameras: We focused on a non-cooling room temperature microbolometer infrared imaging array device which includes a sensing layer of p-type a-Si:H component layers doped with boron. Boron incorporation and bonding configuration were investigated for a-Si:H films grown by plasma enhanced chemical deposition (PECVD) at varying substrate temperatures, hydrogen dilution of the silane precursor, and dopant to silane ratio using multiple internal reflection infrared spectroscopy (MIR-IR). This study was then confirmed from collaborators via Raman spectroscopy. MIR-IR analyses reveal an interesting counter-balance relationship between boron-doping and hydrogen-dilution growth parameters in PECVD-grown a-Si:H. Specifically, an increase in the hydrogen dilution ratio (H2/SiH4) or substrate temperature was found to increase organization of the silicon lattice in the amorphous films. It resulted in the decrease of the most stable SiH bonding configuration and thus decrease the organization of the film. The new chemical bonding information of a-Si:H thin film was correlated with the various boron doping mechanisms proposed by theoretical calculations. The study revealed the corrosion morphology progression on aluminum alloy (Al, 0.5% Cu) under acidic chloride solution. This is due to defects and a higher copper content at the grain boundary. Direct galvanic current measurement, linear sweep voltammetry (LSV), and Tafel plots are used to measure corrosion current and potential. Hydrogen gas evolution was also observed (for the first time) in Cu/Al bimetallic interface in areas of active corrosion. Mechanistic insight that leads to effective prevention of aluminum bond pad corrosion is explored and discussed. (Chapter 4) Aluminum bond pad corrosion activity and mechanistic insight at a Cu/Al bimetallic interface typically used in microelectronic packages for automotive applications were investigated by means of optical and scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX) and electrochemistry. Screening of corrosion variables (temperature, moisture, chloride ion concentration, pH) have been investigated to find their effect on …
Investigation of Post-Plasma Etch Fluorocarbon Residue Characterization, Removal and Plasma-Induced Low-K Damage for Advanced Interconnect Applications: Modern three-dimensional integrated circuit design is rapidly evolving to more complex architecture. With continuous downscaling of devices, there is a pressing need for metrology tool development for rapid but efficient process and material characterization. In this dissertation work, application of a novel multiple internal reflection infrared spectroscopy metrology is discussed in various semiconductor fabrication process development. Firstly, chemical bonding structure of thin fluorocarbon polymer film deposited on patterned nanostructures was elucidated. Different functional groups were identified by specific derivatization reactions and model bonding configuration was proposed for the first time. In a continued effort, wet removal of these fluorocarbon polymer was investigated in presence of UV light. Mechanistic hypothesis for UV-assisted enhanced polymer cleaning efficiency was put forward supported by detailed theoretical consideration and experimental evidence. In another endeavor, plasma-induced damage to porous low-dielectric constant interlayer dielectric material was studied. Both qualitative and quantitative analyses of dielectric degradation in terms of increased silanol content and carbon depletion provided directions towards less aggressive plasma etch and strip process development. Infrared spectroscopy metrology was also utilized in surface functionalization evaluation of very thin organic films deposited by wet and dry chemistries. Palladium binding by surface amine groups was examined in plasma-polymerized amorphous hydrocarbon films and in self-assembled aminosilane thin films. Comparison of amine concentration under different deposition conditions guided effective process optimization. A time- and cost-effective method such as current FTIR metrology that provides in-depth chemical information about thin films, surfaces, interfaces and bulk layers can be increasingly valuable as critical dimensions continue to scale down and subtle process variances begin to have a significant impact on device performance.
Laser Ablation Inductively Coupled Plasma Mass Spectrometry and Raman Spectroscopy Imaging of Biological Tissues: Laser Ablation Inductively coupled plasma mass spectrometry (LA-ICP-MS) and Raman spectroscopy are both powerful imaging techniques. Their applications are numerous and extremely potential in the field of biology. In order to improve upon LA-ICP-MS an in-house built cold cell was developed and its effectiveness studied by imaging Brassica napus seeds. To further apply LA-ICP-MS and Raman imaging to the field of entomology a prong gilled mayfly (Ephemeroptera: Leptophlebiidae) from the Róbalo River, located on Navarino Island in Chile, was studied. Analysis of both samples showcased LA-ICP-MS and Raman spectroscopy as effective instruments for imaging trace elements and larger molecules in biological samples respectively.
Lipidomic Analysis of Single Cells and Organelles Using Nanomanipulation Coupled to Mass Spectrometry: The capability to characterize disease states by way of determining novel biomarkers has led to a high demand of single cell and organelle analytical methodologies due to the unexpected heterogeneity present in cells of the same type. Lipids are of particular interest in the search for biomarkers due to their active roles in cellular metabolism and energy storage. Analyzing localized lipid chemistry from individual cells and organelles is challenging however, due to low analyte volume, limited discriminate instrumentation, and common requirements of separation procedures and expenditure of cell sample. Using nanomanipulation in combination with mass spectrometry, individual cells and organelles can be extracted from tissues and cultures in vitro to determine if heterogeneity at the cellular level is present. The discriminate extraction of a single cell or organelle allows the remainder of cell culture or tissue to remain intact, while the high sensitivity and chemical specificity of mass spectrometry provides structural information for limited volumes without the need for chromatographic separation. Mass analysis of lipids extracted from individual cells can be carried out in multiple mass spectrometry platforms through direct-inject mass spectrometry using nanoelectrospray-ionization and through matrix-assisted laser/desorption ionization.
Synthesis and Electron Transfer Studies of Supramolecular Triads: This study expands the role of polythiophenes as an electron donating chromophore within energy harvesting milti-modular donor-acceptor systems. The polythiophene moiety would act as an electron donating spacer group between the donor and acceptor entities, viz., phenothiazine and fulleropyrrolidine, respectively, in the newly synthesized supramolecular triads. The triads 10-{[2,2';5',2"] terthiophene-5-fulleropyrrolidine} phenothiazine and 10-{[2,2'] bithiophene-5-fulleropyrrolidine} phenothiazine were synthesized and characterized through electrochemical and spectroscopic methods to ascertain their structural integrity. the componets of the triads were selected for their established redox parameters. Phenothiazine would act as a secondary donor and would facilitate hole-transfer from the polythiophene primary electron donor, due to its ease of oxidation and yield a long-lived charge separated state. Fulleropyrrolidine would act as an acceptor for ease of reductive capabilities and its ability to hold multiple charges. Finally, occurrence of photoinduced electron transferleading to the anticipated charge separated states is established from advanced transient spectroscopic techniques on these novel supramolecular systems.
Fundamental Studies of Copper Corrosion in Interconnect Fabrication Process and Spectroscopic Investigation of Low-k Structures: In the first part of this dissertation, copper bimetallic corrosion and its inhibition in cleaning processes involved in interconnect fabrication is explored. In microelectronics fabrication, post chemical mechanical polishing (CMP) cleaning is required to remove organic contaminants and particles left on copper interconnects after the CMP process. Use of cleaning solutions, however, causes serious reliability issues due to corrosion and recession of the interconnects. In this study, different azole compounds are explored and pyrazole is found out to be a potentially superior Cu corrosion inhibitor, compared to the most widely used benzotriazole (BTA), for tetramethyl ammonium hydroxide (TMAH)-based post CMP cleaning solutions at pH 14. Micropattern corrosion screening results and electrochemical impedance spectroscopy (EIS) revealed that 1 mM Pyrazole in 8 wt% TMAH solution inhibits Cu corrosion more effectively than 10 mM benzotriazole (BTA) under same conditions. Moreover, water contact angle measurement results also showed that Pyrazole-treated Cu surfaces are relatively hydrophilic compared to those treated with BTA/TMAH. X-ray photoelectron spectroscopy (XPS) analysis supports Cu-Pyrazole complex formation on the Cu surface. Overall Cu corrosion rate in TMAH-based highly alkaline post CMP cleaning solution is shown to be considerably reduced to less than 1Å/min by addition of 1 mM Pyrazole. In the second part, a novel technique built in-house called multiple internal Reflection Infrared Spectroscopy (MIR-IR) was explored as a characterization tool for characterization of different low-k structures.In leading edge integrated circuit manufacturing, reduction of RC time delay by incorporation of porous ultra low-k interlayer dielectrics into Cu interconnect nanostructure continues to pose major integration challenges. The main challenge is that porous structure renders interlayer dielectrics mechanically weak, chemically unstable and more susceptible to the RIE plasma etching damages. Besides the challenge of handling weak porous ultra low-k materials, a lack of sensitive metrology to guide systematic development of plasma etching, …
Thin Cr2O3 (0001) Films and Co (0001) Films Fabrication for Spintronics: The growth of Co (0001) films and Cr2O3 (0001)/Co (0001) has been investigated using surface analysis methods. Such films are of potential importance for a variety of spintronics applications. Co films were directly deposited on commercial Al2O3 (0001) substrates by magnetron sputter deposition or by molecular beam epitaxy (MBE), with thicknesses of ~1000Å or 30Å, respectively. Low Energy Electron Diffraction (LEED) shows hexagonal (1x1) pattern for expected epitaxial films grown at 800 K to ensure the hexagonally close-packed structure. X-ray photoemission spectroscopy (XPS) indicates the metallic cobalt binding energy for Co (2p3/2) peak, which is at 778.1eV. Atomic force microscopy (AFM) indicates the root mean square (rms) roughness of Co films has been dramatically reduced from 10 nm to 0.6 nm by optimization of experiment parameters, especially Ar pressure during plasma deposition. Ultrathin Cr2O3 films (10 to 25 Å) have been successfully fabricated on 1000Å Co (0001) films by MBE. LEED data indicate Cr2O3 has C6v symmetry and bifurcated spots from Co to Cr2O3 with Cr2O3 thickness less than 6 Å. XPS indicates the binding energy of Cr 2p(3/2) is at 576.6eV which is metallic oxide peak. XPS also shows the growth of Cr2O3 on Co (0001) form a thin Cobalt oxide interface, which is stable after exposure to ambient and 1000K UHV anneal.
Determination of Solute Descriptors for Illicit Drugs Using Gas Chromatographic Retention Data and Abraham Solvation Model: In this experiment, more than one hundred volatile organic compounds were analyzed with the gas chromatograph. Six capillary columns ZB wax plus, ZB 35, TR1MS, TR5, TG5MS and TG1301MS with different polarities have been used for separation of compounds and illicit drugs. The Abraham solvation model has five solute descriptors. The solute descriptors are E, S, A, B, L (or V). Based on the six stationary phases, six equations were constructed as a training set for each of the six columns. The six equations served to calculate the solute descriptors for a set of illicit drugs. Drugs studied are nicotine (S= 0.870, A= 0.000, B= 1.073), oxycodone(S= 2.564. A= 0.286, B= 1.706), methamphetamine (S= 0.297, A= 1.570, B= 1.009), heroin (S=2.224, A= 0.000, B= 2.136) and ketamine (S= 1.005, A= 0.000, B= 1.126). The solute property of Abraham solvation model is represented as a logarithm of retention time, thus the logarithm of experimental and calculated retention times is compared.
Electrochemical Synthesis and Applications of Layered Double Hydroxides and Derivatives: 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 …
Novel Carborane Derived Semiconducting Thin Films for Neutron Detection and Device Applications: 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.
Characterization of Ionic Liquid Solvents Using a Temperature Independent, Ion-Specific Abraham Parameter Model: Experimental data for the logarithm of the gas-to-ionic liquid partition coefficient (log K) have been compiled from the published literature for over 40 ionic liquids over a wide temperature range. Temperature independent correlations based on the Gibbs free energy equation utilizing known Abraham solvation model parameters have been derived for the prediction of log K for 12 ionic liquids to within a standard deviation of 0.114 log units over a temperature range of over 60 K. Temperature independent log K correlations have also been derived from correlations of molar enthalpies of solvation and molar entropies of solvation, each within standard deviations of 4.044 kJ mol-1 and 5.338 J mol-1 K-1, respectively. In addition, molar enthalpies of solvation and molar entropies of solvation can be predicted from the Abraham coefficients in the temperature independent log K correlations to within similar standard deviations. Temperature independent, ion specific coefficients have been determined for 26 cations and 15 anions for the prediction of log K over a temperature range of at least 60 K to within a standard deviation of 0.159 log units.
The Effect of Plasma on Silicon Nitride, Oxynitride and Other Metals for Enhanced Epoxy Adhesion for Packaging Applications: 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.
Electrodeposition of Nickel and Nickel Alloy Coatings with Layered Silicates for Enhanced Corrosion Resistance and Mechanical Properties: 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.
Fundamental Studies of Copper Bimetallic Corrosion in Ultra Large Scale Interconnect Fabrication Process: In this work, copper bimetallic corrosion and inhibition in ultra large scale interconnect fabrication process is explored. Corrosion behavior of physical vapor deposited (PVD) copper on ruthenium on acidic and alkaline solutions was investigated with and without organic inhibitors. Bimetallic corrosion screening experiments were carried out to determine the corrosion rate. Potentiodynamic polarization experiments yielded information on the galvanic couples and also corrosion rates. XPS and FTIR surface analysis gave important information pertaining inhibition mechanism of organic inhibitors. Interestingly copper in contact with ruthenium in cleaning solution led to increased corrosion rate compared to copper in contact with tantalum. On the other hand when cobalt was in contact with copper, cobalt corroded and copper did not. We ascribe this phenomenon to the difference in the standard reduction potentials of the two metals in contact and in such a case a less noble metal will be corroded. The effects of plasma etch gases such as CF4, CF4+O2, C4F8, CH2F2 and SF6 on copper bimetallic corrosion was investigated too in alkaline solution. It was revealed that the type of etching gas plasma chemistry used in Cu interconnect manufacturing process creates copper surface modification which affects corrosion behavior in alkaline solution. The learning from copper bimetallic corrosion studies will be useful in the development of etch and clean formulations that will results in minimum defects and therefore increase the yield and reliability of copper interconnects.
Interfacial Characterization of Chemical Vapor Deposition (Cvd) Grown Graphene and Electrodeposited Bismuth on Ruthenium Surface: Graphene receives enormous attention owing to its distinctive physical and chemical prosperities. Growing and transferring graphene to different substrates have been investigated. The graphene growing on the copper substrate has an advantage of low solubility of carbon on the copper which allow us to grow mostly monolayer graphene. Graphene sheet of few centimeters can be transferred to 300nm silicon oxide and quartz crystal pre-deposited with metal like Cu and Ru. Characterization of the graphene has been done with Raman and contact angle measurement and recently quartz crystal microbalance (QCM) has been employed. The underpotential deposition (UPD) process of Bi on Ru metal surface is studied using electrochemical quartz crystal microbalance (EQCM) and XPS techniques. Both Bi UPD and Bi bulk deposition are clearly observed on Ru in 1mM Bi (NO3)3/0.5M H2SO4. Bi monolayer coverage calculated from mass (MLMass) and from charge (MLCharge) were compared with respect to the potential scanning rates, anions and ambient controls. EQCM results indicate that Bi UPD on Ru is mostly scan rate independent but exhibits interesting difference at the slower scan. Bi UPD monolayer coverage calculated from cathodic frequency change (ΔfCathodic) is significantly smaller than the monolayer coverage derived from integrated charge under the cathodic Bi UPD peak when scan rate is at least 5 mV/s. XPS is utilized to explore the detailed chemical composition of the observed interfacial process of Bi UPD on Ru.
A Study of Silver: an Alternative Maldi Matrix for Low Weight Compounds and Mass Spectrometry Imaging: Soft-landing ion mobility has applicability in a variety of areas. The ability to produce material and collect a sufficient amount for further analysis and applications is the key goal of this technique. Soft-landing ion mobility has provided a way to deposit material in a controllable fashion, and can be tailored to specific applications. Changing the conditions at which soft-landing ion mobility occurs effects the characteristics of the resulting particles (size, distribution/coverage on the surface). Longer deposition times generated more material on the surface; however, higher pressures increased material loss due to diffusion. Larger particles were landed when using higher pressures, and increased laser energy at ablation. The utilization of this technique for the deposition of silver clusters has provided a solvent free matrix application technique for MALDI-MS. The low kinetic energy of incident ions along with the solvent free nature of soft-landing ion mobility lead to a technique capable of imaging sensitive samples and low mass analysis. The lack of significant interference as seen by traditional organic matrices is avoided with the use of metallic particles, providing a major enhancement in the ability to analyze low mass compounds by MALDI.
Carbon Nanostructure Based Donor-acceptor Systems for Solar Energy Harvesting: Carbon nanostructure based functional hybrid molecules hold promise in solarenergy harvesting. Research presented in this dissertation systematically investigates building of various donor-acceptor nanohybrid systems utilizing enriched single walled carbon nanotube and graphene with redox and photoactive molecules such as fullerene, porphyrin, and phthalocyanine. Design, synthesis, and characterization of the donor-acceptor hybrid systems have been carefully performed via supramolecular binding strategies. Various spectroscopic studies have provided ample information in terms of establishment of the formation of donor-acceptor hybrids and their extent of interaction in solution and eventual rate of photoinduced electron and/or energy transfer. Electrochemical studies enabled construction of energy level diagram revealing energetic details of the possible different photochemical events supported by computational studies carried out to establish the HOMO-LUMO levels in the donor acceptor systems. Transient absorption studies confirmed formation of charge separated species in the donor-acceptor systems which have been supported by electron mediation experiments. Based on the photoelectrochemical studies, IPCE of 8% was reported for enriched SWCNT(7,6)-ZnP donor-acceptor systems. In summary, the present investigation on the various nanocarbon sensitized donor-acceptor hybrids substantiates tremendous prospect, that could very well become the next generation of materials in building efficient solar energy harvesting devices andphotocatalyst.
Determination of Molecular Descriptors for Illegal Drugs by Gc-fid Using Abraham Solvation Model: The Abraham solvation parameter model is a good approach for analyzing and predicting biological activities and partitioning coefficients. The general solvation equation has been used to predict the solute property (SP) behavior of drug compounds between biological barriers. Gas chromatography (GC) retention time can be used to predict molecular descriptors, such as E, S, A, B & L for existing and newly developed drug compounds. In this research, six columns of different stationary phases were used to predict the Abraham molecular descriptors more accurately. The six stationary phases used were 5% phenylmethyl polysiloxane, 6% cyanopropylphenyl 94% dimethylpolysiloxane, 5% diphenyl 95% dimethylpolysiloxane, 100% dimethylpolysiloxane, polyethylene glycol and 35% diphenyl 65% dimethylpolysiloxane. Retention times (RT) of 75 compounds have been measured and logarithm of experimental average retention time Ln(RTexp) are calculated. The Abraham solvation model is then applied to predict the process coefficients of these compounds using the literature values of the molecular descriptors (Acree Compilation descriptors). Six correlation equations are built up as a training set for each of the six columns. The six equations are then used to predict the molecular descriptors of the illegal drugs as a test set. This work shows the ability to extract molecular information from a new compound by utilizing commonly used GC columns available with the desired stationary phases. One can simply run the new compound in GC using these columns to get the retention time. Plugging in the retention time into the developed equations for each of the column will predict the molecular descriptors for the test compound and will give some information about the properties of the compound.
Miniature Mass Spectrometry: Theory, Development and Applications: As mass analyzer technology has continued to improve over the last fifty years, the prospect of field-portable mass spectrometers has garnered interest from many research groups and organizations. Designing a field portable instrument entails more than the scaling down of current commercial systems. Additional considerations such as power consumption, vacuum requirements and ruggedization also play key roles. In this research, two avenues were pursued in the initial development of a portable system. First, micrometer-scale mass analyzers and other electrostatic components were fabricated using silicon on insulator-deep reactive ion etching, and tested. Second, the dimensions of an ion trap were scaled to the millimeter level and fabricated from common metals and commercially available vacuum plastics. This instrument was tested for use in ion isolation and collision induced dissociation for secondary mass spectrometry and confirmatory analyses of unknowns. In addition to portable instrumentation, miniature mass spectrometers show potential for usage in process and reaction monitoring. To this end, a commercial residual gas analyzer was used to monitor plasma deposition and cleaning inside of a chamber designed for laser ablation and soft landing-ion mobility to generate metal-main group clusters. This chamber was also equipped for multiple types of spectral analysis in order to identify and characterize the clusters. Finally, a portion of this research was dedicated to method development in sample collection and analysis for forensic study. A new method for the analysis of illicit chemistries collected via electrostatic lifting is presented. This method incorporates surface-enhanced Raman microscopy as a prescreening tool for nanoextraction and nanospray ionization mass spectrometry.
Studies on High Potential Porphyrin-fullerene Supramolecular Dyads: Photoinduced electron transfer in self-assembled via axial coordination porphyrin-fullerene dyads is investigated. Fullerene functionalized with imidazole and fullerenes functionalized with pyridine are chosen as electron acceptors, while zinc pophyrin derivatives are utilized as electron donors. The electron withdrawing ability of halogen atoms make the porphyrin ring electrophilic, which explained the binding of (F20TPP)Zn with fullerene derivatives having the highest binding constant around 105M-1. Another important observation is that the fullerene imidazole binding to zinc pophyrin had higher stability than fullerene pyridine-porphyrin dyad. Computational DFT B3LYP-21G(*) calculations are used to study the geometric and electronic structures. The HOMO and LUMO was found to be located on the porphyrin and fullerene entities, respectively. Photoinduced electron transfer is investigated by the steady-state absorption and emission, differential pulse voltammetry, and nanosecond and femtosecond transient absorption studies. The measurements provided the same conclusion that the increasing number of the halogen atoms on the porphyrin ring leads to the higher binding of porphyrin-fullerene supramolecular dyads and efficient charge separation and charge recombination processes.
Studies on the Porphyrin and Phthalocyanine Modified on Sno2 Photoelectrochemical Cells: The world is facing a tough challenge regarding fulfilling human energy needs. Scientists are motivated to find alternative ways to the fossil fuel at a lower cost with little or no environmental pollution. Among the available renewable resources, the solar energy is an alternative energy to fossil fuel. Scientists are engaged in mimicking the photosynthesis to create the new energy devices such as dye sensitized solar cells. The fundamental theory and properties of the dye sensitized solar cells is given in the first chapter. In this research, the application of the different methods for surface alteration of SnO2 with water soluble porphyrins and phthalocyanine is studied. Using optical absorbance and steady state fluorescence studies, the formation of porphyrins and phthalocyanine discuss on the SnO2 surface is shown. Moreover, the different results of photoelectrochemical cells are show on chapter 2 to understand the porphyrin and phthalocyanine modified on SnO2 as electron injector. In summary, the application porphyrin and phthalocyanine of dimers as a broad band capturing photosensitized dye is discussed.
Substitution Effects of Phenothiazine and Porphyrin Dyes in Dye-sensitized Solar Cells: The details of dye sensitized solar cells was explained and phenothiazine and porphyrin based dyes were synthesized for use in DSSCs. DSSCs offer a unique and cost effective method of renewable energy. DSSCs are characterized through various tests, with the overall efficiency, η, bearing the greatest importance. Incident photon to current conversion efficiency, or IPCE, is also another important characterization of DSSCs. Effect of positioning of the cyanoacrylic acid anchoring group on ring periphery of phenothiazine dye on the performance of dye sensitized solar cells (DSSCs) is reported. The performances of the cells are found to be prominent for solar cells made out of Type-1 dyes compared to Type-2 dyes. This trend has been rationalized based on spectral, electrochemical, computational and electrochemical impedance spectroscopy results. Free-base and zinc porphyrins bearing a carboxyl anchoring group at the para, meta, or ortho positions of one of the meso-phenyl rings were synthesized for DSSCs. Photoelectrochemical studies were performed after immobilization of porphyrins onto nanocrystalline TiO2. The performance of DSSCs with the porphyrin anchoring at the para or meta position were found to greatly exceed those in the ortho position. Additionally, zinc porphyrin derivatives outperformed the free-base porphyrin analogs, including better dye regeneration efficiency for the zinc porphyrin derivatives and for the meta and para derivatives through electrochemical impedance spectroscopy studies. The overall structure-performance trends observed for the present porphyrin DSSCs have been rationalized based on spectral, electrochemical, electrochemical impedance spectroscopy and transient spectroscopy results.
Development of Novel Semi-conducting Ortho-carborane Based Polymer Films: Enhanced Electronic and Chemical Properties: 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.
Electrochemically Deposited Metal Alloy-silicate Nanocomposite Corrosion Resistant Materials: Zinc-nickel ?-phase silicate and copper-nickel silicate corrosion resistant coatings have been prepared via electrochemical methods to improve currently available corrosion resistant materials in the oil and gas industry. A layered silicate, montmorillonite, has been incorporated into the coatings for increased corrosion protection. For the zinc nickel silicate coatings, optimal plating conditions were determined to be a working pH range of 9.3 -9.5 with a borate based electrolyte solution, resulting in more uniform deposits and better corrosion protection of the basis metal as compared to acidic conditions. Quality, strongly adhering deposits were obtained quickly with strong, even overall coverage of the metal substrate. The corrosion current of the zinc-nickel-silicate coating is Icorr = 3.33E-6 for a borate based bath as compared to a zinc-nickel bath without silicate incorporation (Icorr = 3.52E-5). Step potential and direct potential methods were examined, showing a morphological advantage to step potential deposition. The effect of borate addition was examined in relation to zinc, nickel and zinc-nickel alloy deposition. Borate was found to affect the onset of hydrogen evolution and was examined for absorption onto the electrode surface. For copper-nickel silicate coatings, optimal conditions were determined to be a citrate based electrolytic bath, with pH = 6. The solutions were stable over time and strong adhering, compact particle deposits were obtained. The corrosion current of the copper-nickel-silicate coatings is Icorr = 3.86E-6 (copper-nickel coatings without silicate, Icorr = 1.78E-4). The large decrease in the corrosion current as the silicate is incorporated into the coating demonstrates the increase in corrosion resistance of the coatings with the incorporation of silicates.
Development of a Laponite Pluronic Composite for Foaming Applications: The focus of the following research was to provide an optimized particle stabilized foam of Laponite and Pluronic L62 in water by understanding (1) the Laponite-Pluronic interactions and properties for improved performance in a particle stabilized foam and (2) the interfacial properties between air and the Laponite-Pluronic complex. These studies were conducted using both bulk and interfacial rheology, XRD, sessile droplet, TGA and UV-vis. Two novel and simple techniques, lamella break point and capillary breakup extensional rheometry, were used to both understand the Laponite Pluronic L62 interaction and determine a different mechanism for foaming properties. Bulk rheological properties identified an optimal Laponite concentration of 2% with Pluronic L62 ranging from 2.5% and 6.5%, due to the ease of flow for the dispersion. The Pluronic L62 was observed to enhance the Laponite bulk rheological properties in solution. Additionally TGA showed a similar trend in thermal resistance to water with both addition of Laponite and Pluronic L62. XRD demonstrated that 0.25% Pluronic intercalated into Laponite from dried 2% Laponite films. XRD demonstrated that the Laponite matrix was saturated at 1% Pluronic L62. UV-vis demonstrated that a monolayer of Pluronic L62 is observed up to 0.65% Pluronic L62 onto Laponite. Interfacial rheology showed that Laponite enhances Pluronic L62 at the air-liquid interface by improving the storage modulus as low at 0.65% Pluronic L62 with 2% Laponite. The lamella breakpoint of Laponite with Pluronic films indicate strong film interaction due to higher increases in mass. Extensional rheology indicates that 2.5% to 6.5% Pluronic with 2% Laponite show the most filament resistance to stretching.
Investigation of Novel Electrochemical Synthesis of Bioapatites and Use in Elemental Bone Analysis: In this research, electrochemical methods are used to synthesize the inorganic fraction of bone, hydroxyapatite, for application in biological implants and as a calibration material for elemental analysis in human bone. Optimal conditions of electrochemically deposited uniform apatite coatings on stainless steel were investigated. Apatite is a ceramic with many different phases and compositions that have beneficial characteristics for biomedical applications. Of those phases hydroxyapatite (HA) is the most biocompatible and is the primary constituent of the inorganic material in bones. HA coatings on metals and metal alloys have the ability to bridge the growth between human tissues and implant interface, where the metal provides the strength and HA provides the needed bioactivity. The calcium apatites were electrochemically deposited using a modified simulated body fluid adjusted to pH 4-10, for 1-3 hours at varying temperature of 25-65°C while maintaining cathodic potentials of -1.0 to -1.5V. It was observed that the composition and morphology of HA coatings change during deposition by the concentration of counter ions in solution, pH, temperature, applied potential, and post-sintering. The coatings were characterized by powder x-ray diffraction, Fourier transform infrared spectroscopy, and scanning electron microscopy. The precipitated powders from the experiment were also characterized, with results showing similarities to biological apatite. There is a need for quantitative elemental analysis of calcified biological matrices such as bone and teeth; however there are no suitable calibration materials commercially available for quantitative analysis. Matrix-matched standards are electrochemically synthesized for LA-ICP-MS analysis of human bone. The synthetic bioapatite is produced via a hydrothermal electrochemical process using a simulated body fluid solution to form hydroxyapatite. Additional bioapatite standards are synthesized containing trace amounts of metals. The x-ray diffraction of the synthesized standards shows an increase in cell volume for the crystal structure from 0.534 to 0.542 nm3 with the substitution of …
Study of Novel Ion/surface Interactions Using Soft-landing Ion Mobility: Preparative mass spectrometry is a gas-phase ion deposition technique aimed at deposition of monodisperse ion beams on a surface. This is accomplished through the implementation of a soft-landing ion mobility system which allows for high ion flux of conformationally selected ion packets. The soft-landing ion mobility system has been applied to a number of unique chemical problems including the deposition of insulators on graphene, the preparation of reusable surface enhanced Raman spectroscopic substrates, and the deposition of uranium nanoparticles. Soft-landing ion mobility provided a platform for the quick deposition of usable amounts of materials, which is the major objective of preparative mass spectrometry. Soft-landing ion mobility is unique when compared to other preparative mass spectrometric techniques in that the ion packets are conformationally separated, not separated on mass to charge ratio. This provides orthogonal complementary data to traditional mass spectrometric techniques and allows for the study of conformationally monodisperse surfaces. The diversity of problems that have been and continued to be explored with soft-landing ion mobility highlight the utility of the technique as a novel tool for the study of multiple ion/surface interactions.
Supramolecular Solar Cells: Supramolecular chemistry - chemistry of non-covalent bonds including different type of intermolecular interactions viz., ion-pairing, ion-dipole, dipole-dipole, hydrogen bonding, cation-p and Van der Waals forces. Applications based on supramolecular concepts for developing catalysts, molecular wires, rectifiers, photochemical sensors have been evolved during recent years. Mimicking natural photosynthesis to build energy harvesting devices has become important for generating energy and solar fuels that could be stored for future use. In this dissertation, supramolecular chemistry is being explored for creating light energy harvesting devices. Photosensitization of semiconductor metal oxide nanoparticles, such as titanium dioxide (TiO2) and tin oxide (SnO2,), via host-guest binding approach has been explored. In the first part, self-assembly of different porphyrin macrocyclic compounds on TiO2 layer using axial coordination approach is explored. Supramolecular dye sensitized solar cells built based on this approach exhibited Incident Photon Conversion Efficiency (IPCE) of 36% for a porphyrin-ferrocene dyad. In the second part, surface modification of SnO2 with water soluble porphyrins and phthalocyanine resulted in successful self-assembly of dimers on SnO2 surface. IPCE more than 50% from 400 - 700 nm is achieved for the supramolecular self-assembled heterodimer photocells is achieved. In summary, the axial ligation and ion-pairing method used as supramolecular tools to build photocells, exhibited highest quantum efficiency of light energy conversion with panchromatic spectral coverage. The reported findings could be applied to create interacting molecular systems for next generation of efficient solar energy harvesting devices.
Electrochemical Depostion of Bismuth on Ruthenium and Ruthenium Oxide Surfaces: Cyclic voltammetry experiments were performed to compare the electrodeposition characteristics of bismuth on ruthenium. Two types of electrodes were used for comparison: a Ru shot electrode (polycrystalline) and a thin film of radio-frequency sputtered Ru on a Ti/Si(100) support. Experiments were performed in 1mM Bi(NO3)3/0.5M H2SO4 with switching potentials between -0.25 and 0.55V (vs. KCl sat. Ag/AgCl) and a 20mV/s scan rate. Grazing incidence x-ray diffraction (GIXRD) determined the freshly prepared thin film electrode was hexagonally close-packed. After thermally oxidizing at 600°C for 20 minutes, the thin film adopts the tetragonal structure consistent with RuO2. a hydrated oxide film (RuOx?(H2O)y) was made by holding 1.3V on the surface of the film in H2SO4 for 60 seconds and was determined to be amorphous. Underpotential deposition of Bi was observed on the metallic surfaces and the electrochemically oxidized surface; it was not observed on the thermal oxide.
Experimental Determination of L, Ostwald Solubility Solute Descriptor for Illegal Drugs By Gas Chromatography and Analysis By the Abraham Model: The experiment successfully established the mathematical correlations between the logarithm of retention time of illegal drugs with GC system and the solute descriptor L from the Abraham model. the experiment used the method of Gas Chromatography to analyze the samples of illegal drugs and obtain the retention time of each one. Using the Abraham model to calculate and analyze the sorption coefficient of illegal drugs is an effective way to estimate the drugs. Comparison of the experimental data and calculated data shows that the Abraham linear free energy relationship (LFER) model predicts retention behavior reasonably well for most compounds. It can calculate the solute descriptors of illegal drugs from the retention time of GC system. However, the illegal drugs chosen for this experiment were not all ideal for GC analysis. HPLC is the optimal instrument and will be used for future work. HPLC analysis of the illegal drug compounds will allow for the determination of all the solute descriptors allowing one to predict the illegal drugs behavior in various Abraham biological and medical equations. the results can be applied to predict the properties in biological and medical research which the data is difficult to measure. the Abraham model will predict more accurate results by increasing the samples with effective functional groups.
Incorporating Electrochemistry and X-ray Diffraction Experiments Into an Undergraduate Instrumental Analysis Course: Experiments were designed for an undergraduate instrumental analysis laboratory course, two in X-ray diffraction and two in electrochemistry. Those techniques were chosen due their underrepresentation in the Journal of Chemical Education. Paint samples (experiment 1) and pennies (experiment 2) were characterized using x-ray diffraction to teach students how to identify different metals and compounds in a sample. in the third experiment, copper from a penny was used to perform stripping analyses at different deposition times. As the deposition time increases, the current of the stripping peak also increases. the area under the stripping peak gives the number of coulombs passed, which allows students to calculate the mass of copper deposited on the electrode surface. the fourth experiment was on the effects of variable scan rates on a chemical system. This type of experiment gives valuable mechanistic information about the chemical system being studied.
Electrochemical Quartz Crystal Microbalance Study Of Bismuth Underpotential Deposition On Ruthenium And On Electrochemically Formed Ruthenium Oxide: Kinetics and thermodynamics of bismuth (Bi) underpotential deposition (UPD) on ruthenium (Ru) and on electrochemically formed Ru oxide are studied using electrochemical quartz crystal microbalance technique. The Bi UPD and Bi bulk deposition are observed both on Ru and on electrochemically formed Ru oxide electrodes. The anodic peak potential of Bi UPD shifts slightly to positive potential as the scan rate increases. The peak current ratio (IAnode/ICathode) of Bi UPD and Bi bulk increases as the scan rate increases. Bi monolayer coverage calculated from mass (MLMass) and from charge (MLCharge) with scan rates dependent are compared both in Bi UPD region and in Bi bulk region. Stability and oxidation time effects are also investigated. Bi UPD on Ru and on electrochemically formed Ru oxide are quasi-reversible, scan rate independent, oxidation time dependent, and have higher plating efficiency on Ru. However, Bi bulk deposition on Ru and on electrochemically formed Ru oxide are quasi-reversible, scan rate dependent, oxidation time independent, and have higher plating efficiency on electrochemically formed Ru oxide. Both Bi UPD adatoms and Bi bulk are unstable in 0.5M H2SO4.
Boron Nitride by Atomic Layer Deposition: A Template for Graphene Growth: 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.
Cu Electrodeposition on Ru-Ta and Corrosion of Plasma Treated Cu in Post Etch Cleaning Solution: 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.
Design and Development of Soft Landing Ion Mobility: A Novel Instrument for Preparative Material Development: 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.
Interfacial Electrochemistry of Copper and Spectro-Electrochemical Characterization of Oxygen Reduction Reaction: 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.
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: 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.
Characterization of Novel Solvents and Absorbents for Chemical Separations: Predictive methods have been employed to characterize chemical separation mediums including solvents and absorbents. These studies included creating Abraham solvation parameter models for room-temperature ionic liquids (RTILs) utilizing novel ion-specific and group contribution methodologies, polydimethyl siloxane (PDMS) utilizing standard methodology, and the micelles cetyltrimethylammonium bromide (CTAB) and sodium dodecylsulfate (SDS) utilizing a combined experimental setup methodology with indicator variables. These predictive models allows for the characterization of both standard and new chemicals for use in chemical separations including gas chromatography (GC), solid phase microextraction (SPME), and micellar electrokinetic chromatography (MEKC). Gas-to-RTIL and water-to-RTIL predictive models were created with a standard deviation of 0.112 and 0.139 log units, respectively, for the ion-specific model and with a standard deviation of 0.155 and 0.177 log units, respectively, for the group contribution fragment method. Enthalpy of solvation for solutes dissolved into ionic liquids predictive models were created with ion-specific coefficients to within standard deviations of 1.7 kJ/mol. These models allow for the characterization of studied ionic liquids as well as prediction of solute-solvent properties of previously unstudied ionic liquids. Predictive models were created for the logarithm of solute's gas-to-fiber sorption and water-to-fiber sorption coefficient for polydimethyl siloxane for wet and dry conditions. These models were created to standard deviations of 0.198 and 0.122 logunits for gas-to-PDMS wet and dry, respectively, as well as 0.164 and 0.134 log units for water-to-PDMS wet and dry, respectively. These models are particularly useful in solid phase microextraction separations. Micelles were studied to create predictive models of the measured micelle-water partition coefficient as well as models of measured MEKC chromatographic retention factors for CTAB and SDS. The resultant predictive models were created with standard deviations of 0.190 log units for the logarithm of the mole fraction concentration of water-to-CTAB, 0.171 log units for the combined logarithms of both the …
The Development of an Analytical Microwave Electromagnetic Pulse Transmission Probe and Preliminary Test Results: Within this educational endeavor instrumental development was explored through the investigation of microwave induce stable electromagnetic waves within a non-linear yttrium iron garnet ferromagnetic waveguide. The resulting magnetostatic surface waves were investigated as a possible method of rapid analytical evaluation of material composition. Initial analytical results indicate that the interaction seen between wave and material electric and magnetic fields will allow phase coherence recovery andanalysis leading to enhancement of analytical value. The ferromagnetic waveguide selected for this research was a high quality monocrystalline YIG (yttrium iron garnet) film. Magnetostatic spin waves (MSW) were produced within the YIG thin waveguide. Spin waves with desired character were used to analytically scan materials within the liquid and solid phase.
Forensic Science Applications Utilizing Nanomanipulation-Coupled to Nanospray Ionization-Mass Spectrometry for the Analysis of Ultra-Trace Illicit Drugs: Presented in this thesis are two methods that are coupled to the instrumentation for the recovery and analysis of ultra-trace illicit drug residues. The electrostatic dust lifting process is coupled with nanomanipulation-nanospray ionization to retrieve drug particles off of hard surfaces for analysis. For the second method, drug residues from fingerprint impressions are extracted followed by analysis. The methodology of these hyphenated techniques toward forensic science applications is applied as to explore limits of detection, sensitivity, and selectivity of analytes as well as immediacy and efficiency of analysis. The application of nanomanipulation-coupled to nanospray ionization-mass spectrometry toward forensic science based applications is considered as future improvements to trace and ultra-trace analysis.
Soft Landing Ion Mobility Mass Spectrometry: History, Instrumentation and an Ambient Pressure Application: Preparative mass spectrometry is an important method for the synthesis of new materials. Recently, soft landing mass spectrometry has been used to land ions on surfaces to coat or otherwise alter them. Commercial soft landing instruments do not yet exist, and the physical phenomenon of soft landing has not yet been fully described. For future ion mobility soft landing research, the theory of ion mobility, ion optics and soft landing is discussed, and 2 soft landing instruments have been built and described, along with proof of concept experiments for both instruments. Simulations of the process of ion mobility and ion optics for use in these instruments, as well as some preliminary results for the optics are included. Surfaces described include copper on mica and iron on silicon. Self assembly of soft landed ions is observed on the surfaces. The instruments constructed will be useful for future soft landing research, and soft landing can be used for future materials research with special attention focused on the self-assembly of the landed ions.

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