Matching Items (719)
Filtering by
- All Subjects: Materials Science
- All Subjects: Chemistry
- Creators: Arizona State University
Description
Over the last decade copper electrodeposition has become the dominant process by which microelectronic interconnects are made. Replacing ultra-high vacuum evaporative film growth, the technology known as the Cu damascene process has been widely implemented in the microelectronics industry since the early 2000s. The transition from vacuum film growth to electrodeposition was enabled by solution chemistries that provide "bottom-up" or superfilling capability of vias and trenches. While the process has been and is used widely, the actual mechanisms responsible for superfilling remain relatively unknown. This dissertation presents and discusses the background and results of experimental investigations that have been done using in situ electrochemical surface stress monitoring techniques to study the evolution of stress on Cu{111} thin film electrodes. Because of its extreme sensitivity to the structure on both the electrode and solution sides of the interface, surface stress monitoring as analytical technique is well suited for the study of electrodeposition. These ultra-high resolution stress measurements reveal the dynamic response of copper electrodes to a number of electrochemical and chemical experimental variables. In the case of constant current pulsed deposition and stripping, the surface stress evolution depends not only on the magnitude of the current pulse, but also shows a marked response to plating bath composition. The plating bath chemistries used in this work include (1) additive free, (2) deposition suppressing solutions that include polyethylene glycol (PEG) and sodium chloride (NaCl) as well as (3) full additive solution combinations which contain PEG, NaCl, and a one of two deposition accelerating species (bis-(sodiumsulfopropyl)disulfide (SPS) or mercaptopropane sulfonic acid (MPS)). The development of thin film stress is further investigated through a series of solution exchange experiments that correlate the magnitude of electrode exchange current density and the stress state of the film. Remarkably, stress changes as large as ~8.5 N/m are observed during solution exchanges at the open circuit potential. Overall, this research demonstrates that solution chemistry can have a large impact on thin film stress evolution, even for very small deposition thicknesses (e.g. <10 ML) or in the absence of net addition or removal of material from the electrode.
ContributorsHeaton, Thomas Stanley (Author) / Friesen, Cody (Thesis advisor) / Buttry, Daniel (Committee member) / Sieradzki, Karl (Committee member) / Arizona State University (Publisher)
Created2011
Description
Increasing demand for high strength powder metallurgy (PM) steels has resulted in the development of dual phase PM steels. In this work, the effects of thermal aging on the microstructure and mechanical behavior of dual phase precipitation hardened powder metallurgy (PM) stainless steels of varying ferrite-martensite content were examined. Quantitative analyses of the inherent porosity and phase fractions were conducted on the steels and no significant differences were noted with respect to aging temperature. Tensile strength, yield strength, and elongation to fracture all increased with increasing aging temperature reaching maxima at 538oC in most cases. Increased strength and decreased ductility were observed in steels of higher martensite content. Nanoindentation of the individual microconstituents was employed to obtain a fundamental understanding of the strengthening contributions. Both the ferrite and martensite hardness values increased with aging temperature and exhibited similar maxima to the bulk tensile properties. Due to the complex non-uniform stresses and strains associated with conventional nanoindentation, micropillar compression has become an attractive method to probe local mechanical behavior while limiting strain gradients and contributions from surrounding features. In this study, micropillars of ferrite and martensite were fabricated by focused ion beam (FIB) milling of dual phase precipitation hardened powder metallurgy (PM) stainless steels. Compression testing was conducted using a nanoindenter equipped with a flat punch indenter. The stress-strain curves of the individual microconstituents were calculated from the load-displacement curves less the extraneous displacements of the system. Using a rule of mixtures approach in conjunction with porosity corrections, the mechanical properties of ferrite and martensite were combined for comparison to tensile tests of the bulk material, and reasonable agreement was found for the ultimate tensile strength. Micropillar compression experiments of both as sintered and thermally aged material allowed for investigation of the effect of thermal aging.
ContributorsStewart, Jennifer (Author) / Chawla, Nikhilesh (Thesis advisor) / Jiang, Hanqing (Committee member) / Krause, Stephen (Committee member) / Arizona State University (Publisher)
Created2011
Description
In recent years, the field of nanomedicine has progressed at an astonishing rate, particularly with respect to applications in cancer treatment and molecular imaging. Although organic systems have been the frontrunners, inorganic systems have also begun to show promise, especially those based upon silica and magnetic nanoparticles (NPs). Many of these systems are being designed for simultaneous therapeutic and diagnostic capabilities, thus coining the term, theranostics. A unique class of inorganic systems that shows great promise as theranostics is that of layered double hydroxides (LDH). By synthesis of a core/shell structures, e.g. a gold nanoparticle (NP) core and LDH shell, the multifunctional theranostic may be developed without a drastic increase in the structural complexity. To demonstrate initial proof-of-concept of a potential (inorganic) theranostic platform, a Au-core/LDH-shell nanovector has been synthesized and characterized. The LDH shell was heterogeneously nucleated and grown on the surface of silica coated gold NPs via a coprecipitation method. Polyethylene glycol (PEG) was introduced in the initial synthesis steps to improve crystallinity and colloidal stability. Additionally, during synthesis, fluorescein isothiocyanate (FITC) was intercalated into the interlayer spacing of the LDH. In contrast to the PEG stabilization, a post synthesis citric acid treatment was used as a method to control the size and short-term stability. The heterogeneous core-shell system was characterized with scanning electron microscopy (SEM), energy dispersive x-ray spectroscopy (EDX), dynamic light scattering (DLS), and powder x-ray diffraction (PXRD). A preliminary in vitro study carried out with the assistance of Dr. Kaushal Rege's group at Arizona State University was to demonstrate the endocytosis capability of homogeneously-grown LDH NPs. The DLS measurements of the core-shell NPs indicated an average particle size of 212nm. The PXRD analysis showed that PEG greatly improved the crystallinity of the system while simultaneously preventing aggregation of the NPs. The preliminary in vitro fluorescence microscopy revealed a moderate uptake of homogeneous LDH NPs into the cells.
ContributorsRearick, Colton (Author) / Dey, Sandwip K (Thesis advisor) / Krause, Stephen (Committee member) / Ramakrishna, B (Committee member) / Arizona State University (Publisher)
Created2011
Description
A new challenge on the horizon is to utilize the large amounts of protein found in the atmosphere to identify different organisms from which the protein originated. Included here is work investigating the presence of identifiable patterns of different proteins collected from the air and biological samples for the purposes of remote identification. Protein patterns were generated using high performance liquid chromatography (HPLC). Patterns created could identify high-traffic and low-traffic indoor spaces. Samples were collected from the air using air pumps to draw air through a filter paper trapping particulates, including large amounts of shed protein matter. In complimentary research aerosolized biological samples were collected from various ecosystems throughout Ecuador to explore the relationship between environmental setting and aerosolized protein concentrations. In order to further enhance protein separation and produce more detailed patterns for the identification of individual organisms of interest; a novel separation device was constructed and characterized. The separation device incorporates a longitudinal gradient as well as insulating dielectrophoretic features within a single channel. This design allows for the production of stronger local field gradients along a global gradient allowing particles to enter, initially transported through the channel by electrophoresis and electroosmosis, and to be isolated according to their characteristic physical properties, including charge, polarizability, deformability, surface charge mobility, dielectric features, and local capacitance. Thus, different types of particles are simultaneously separated at different points along the channel distance given small variations of properties. The device has shown the ability to separate analytes over a large dynamic range of size, from 20 nm to 1 μm, roughly the size of proteins to the size of cells. In the study of different sized sulfate capped polystyrene particles were shown to be selectively captured as well as concentrating particles from 103 to 106 times. Qualitative capture and manipulation of β-amyloid fibrils were also shown. The results demonstrate the selective focusing ability of the technique; and it may form the foundation for a versatile tool for separating complex mixtures. Combined this work shows promise for future identification of individual organisms from aerosolized protein as well as for applications in biomedical research.
ContributorsStaton, Sarah J. R (Author) / Hayes, Mark A. (Committee member) / Anbar, Ariel D (Committee member) / Shock, Everett (Committee member) / Williams, Peter (Committee member) / Arizona State University (Publisher)
Created2011
Description
The Santa Gertrudis Mining District of Sonora, Mexico contains more than a dozen purported Carlin-like, sedimentary-hosted, disseminated-gold deposits. A series of near-surface, mostly oxidized gold deposits were open-pit mined from the calcareous and clastic units of the Cretaceous Bisbee Group. Gold occurs as finely disseminated, sub-micron coatings on sulfides, associated with argillization and silicification of calcareous, carbonaceous, and siliciclastic sedimentary rocks in structural settings. Gold occurs with elevated levels of As, Hg, Sb, Pb, and Zn. Downhole drill data within distal disseminated gold zones reveal a 5:1 ratio of Ag:Au and strong correlations of Au to Pb and Zn. This study explores the timing and structural control of mineralization utilizing field mapping, geochemical studies, drilling, core logging, and structural analysis. Most field evidence indicates that mineralization is related to a single pulse of moderately differentiated, Eocene intrusives described as Mo-Cu-Au skarn with structurally controlled distal disseminated As-Ag-Au.
ContributorsGeier, John Jeffrey (Author) / Reynolds, Stephen J. (Thesis advisor) / Burt, Donald (Committee member) / Stump, Edmund (Committee member) / Arizona State University (Publisher)
Created2011
Description
Atmospheric particulate matter has a substantial impact on global climate due to its ability to absorb/scatter solar radiation and act as cloud condensation nuclei (CCN). Yet, little is known about marine aerosol, in particular, the carbonaceous fraction. In the present work, particulate matter was collected, using High Volume (HiVol) samplers, onto quartz fiber substrates during a series of research cruises on the Atlantic Ocean. Samples were collected on board the R/V Endeavor on West–East (March–April, 2006) and East–West (June–July, 2006) transects in the North Atlantic, as well as on the R/V Polarstern during a North–South (October–November, 2005) transect along the western coast of Europe and Africa. The aerosol total carbon (TC) concentrations for the West–East (Narragansett, RI, USA to Nice, France) and East–West (Heraklion, Crete, Greece to Narragansett, RI, USA) transects were generally low over the open ocean (0.36±0.14 μg C/m3) and increased as the ship approached coastal areas (2.18±1.37 μg C/m3), due to increased terrestrial/anthropogenic aerosol inputs. The TC for the North–South transect samples decreased in the southern hemisphere with the exception of samples collected near the 15th parallel where calculations indicate the air mass back trajectories originated from the continent. Seasonal variation in organic carbon (OC) was seen in the northern hemisphere open ocean samples with average values of 0.45 μg/m3 and 0.26 μg/m3 for spring and summer, respectively. These low summer time values are consistent with SeaWiFS satellite images that show decreasing chlorophyll a concentration (a proxy for phytoplankton biomass) in the summer. There is also a statistically significant (p<0.05) decline in surface water fluorescence in the summer. Moreover, examination of water–soluble organic carbon (WSOC) shows that the summer aerosol samples appear to have a higher fraction of the lower molecular weight material, indicating that the samples may be more oxidized (aged). The seasonal variation in aerosol content seen during the two 2006 cruises is evidence that a primary biological marine source is a significant contributor to the carbonaceous particulate in the marine atmosphere and is consistent with previous studies of clean marine air masses.
ContributorsHill, Hansina Rae (Author) / Herckes, Pierre (Thesis advisor) / Westerhoff, Paul (Committee member) / Hartnett, Hilairy (Committee member) / Arizona State University (Publisher)
Created2011
Description
This work investigates in-situ stress evolution of interfacial and bulk processes in electrochemical systems, and is divided into two projects. The first project examines the electrocapillarity of clean and CO-covered electrodes. It also investigates surface stress evolution during electro-oxidation of CO at Pt{111}, Ru/Pt{111} and Ru{0001} electrodes. The second project explores the evolution of bulk stress that occurs during intercalation (extraction) of lithium (Li) and formation of a solid electrolyte interphase during electrochemical reduction (oxidation) of Li at graphitic electrodes. Electrocapillarity measurements have shown that hydrogen and hydroxide adsorption are compressive on Pt{111}, Ru/Pt{111}, and Ru{0001}. The adsorption-induced surface stresses correlate strongly with adsorption charge. Electrocatalytic oxidation of CO on Pt{111} and Ru/Pt{111} gives a tensile surface stress. A numerical method was developed to separate both current and stress into background and active components. Applying this model to the CO oxidation signal on Ru{0001} gives a tensile surface stress and elucidates the rate limiting steps on all three electrodes. The enhanced catalysis of Ru/Pt{111} is confirmed to be bi-functional in nature: Ru provides adsorbed hydroxide to Pt allowing for rapid CO oxidation. The majority of Li-ion batteries have anodes consisting of graphite particles with polyvinylidene fluoride (PVDF) as binder. Intercalation of Li into graphite occurs in stages and produces anisotropic strains. As batteries have a fixed size and shape these strains are converted into mechanical stresses. Conventionally staging phenomena has been observed with X-ray diffraction and collaborated electrochemically with the potential. Work herein shows that staging is also clearly observed in stress. The Li staging potentials as measured by differential chronopotentiometry and stress are nearly identical. Relative peak heights of Li staging, as measured by these two techniques, are similar during reduction, but differ during oxidation due to non-linear stress relaxation phenomena. This stress relaxation appears to be due to homogenization of Li within graphite particles rather than viscous flow of the binder. The first Li reduction wave occurs simultaneously with formation of a passivating layer known as the solid electrolyte interphase (SEI). Preliminary experiments have shown the stress of SEI formation to be tensile (~+1.5 MPa).
ContributorsMickelson, Lawrence (Author) / Friesen, Cody (Thesis advisor) / Sieradzki, Karl (Committee member) / Buttry, Daniel (Committee member) / Venables, John (Committee member) / Arizona State University (Publisher)
Created2011
Description
The challenging search for clean, reliable and environmentally friendly energy sources has fueled increased research in thermoelectric materials, which are capable of recovering waste heat. Among the state-of-the-art thermoelectric materials β-Zn4Sb3 is outstanding because of its ultra-low glass-like thermal conductivity. Attempts to explore ternary phases in the Zn-Sb-In system resulted in the discovery of the new intermetallic compounds, stable Zn5Sb4In2-δ (δ=0.15) and metastable Zn9Sb6In2. Millimeter-sized crystals were grown from molten metal fluxes, where indium metal was employed as a reactive flux medium.Zn5Sb4In2-δ and Zn9Sb6In2 crystallize in new structure types featuring complex framework and the presence of structural disorder (defects and split atomic positions). The structure and phase relations between ternary Zn5Sb4In2-δ, Zn9Sb6In2 and binary Zn4Sb3 are discussed. To establish and understand structure-property relationships, thermoelectric properties measurements were carried out. The measurements suggested that Zn5Sb4In2-δ and Zn9Sb6In2 are narrow band gap semiconductors, similar to β-Zn4Sb3. Also, the peculiar low thermal conductivity of Zn4Sb3 (1 W/mK) is preserved. In the investigated temperature range 10 to 350 K Zn5Sb4In2-δ displays higher thermoelectric figure of merits than Zn4Sb3, indicating a potential significance in thermoelectric applications. Finally, the glass-like thermal conductivities of binary and ternary antimonides with complex structures are compared and the mechanism behind their low thermal conductivities is briefly discussed.
ContributorsWu, Yang (Author) / Häussermann, Ulrich (Thesis advisor) / Seo, Dong (Committee member) / Petuskey, William T (Committee member) / Newman, Nathan (Committee member) / Arizona State University (Publisher)
Created2011
Description
This thesis discusses the use of low temperature microwave anneal as an alternative technique to recrystallize materials damaged or amorphized due to implantation techniques. The work focuses on the annealing of high-Z doped Si wafers that are incapable of attaining high temperatures required for recrystallizing the damaged implanted layers by microwave absorption The increasing necessity for quicker and more efficient processing techniques motivates study of the use of a single frequency applicator microwave cavity along with a Fe2O3 infused SiC-alumina susceptor/applicator as an alternative post implantation process. Arsenic implanted Si samples of different dopant concentrations and implantation energies were studied pre and post microwave annealing. A set of as-implanted Si samples were also used to assess the effect of inactive dopants against presence of electrically active dopants on the recrystallization mechanisms. The extent of damage repair and Si recrystallization of the damage caused by arsenic and Si implantation of Si is determined by cross-section transmission electron microscopy and Raman spectroscopy. Dopant activation is evaluated for the As implanted Si by sheet resistance measurements. For the same, secondary ion mass spectroscopy analysis is used to compare the extent of diffusion that results from such microwave annealing with that experienced when using conventional rapid thermal annealing (RTA). Results show that compared to susceptor assisted microwave annealing, RTA caused undesired dopant diffusion. The SiC-alumina susceptor plays a predominant role in supplying heat to the Si substrate, and acts as an assistor that helps a high-Z dopant like arsenic to absorb the microwave energy using a microwave loss mechanism which is a combination of ionic and dipole losses. Comparisons of annealing of the samples were done with and without the use of the susceptor, and confirm the role played by the susceptor, since the samples donot recrystallize when the surface heating mechanism provided by the susceptor is not incorporated. Variable frequency microwave annealing was also performed over the as-implanted Si samples for durations and temperatures higher than the single frequency microwave anneal, but only partial recrystallization of the damaged layer was achieved.
ContributorsVemuri, Rajitha (Author) / Alford, Terry L. (Thesis advisor) / Theodore, David (Committee member) / Krause, Stephen (Committee member) / Arizona State University (Publisher)
Created2011
Description
Nucleosomes are the basic repetitive unit of eukaryotic chromatin and are responsible for packing DNA inside the nucleus of the cell. They consist of a complex of eight histone proteins (two copies of four proteins H2A, H2B, H3 and H4) around which 147 base pairs of DNA are wrapped in ~1.67 superhelical turns. Although the nucleosomes are stable protein-DNA complexes, they undergo spontaneous conformational changes that occur in an asynchronous fashion. This conformational dynamics, defined by the "site-exposure" model, involves the DNA unwrapping from the protein core and exposing itself transiently before wrapping back. Physiologically, this allows regulatory proteins to bind to their target DNA sites during cellular processes like replication, DNA repair and transcription. Traditional biochemical assays have stablished the equilibrium constants for the accessibility to various sites along the length of the nucleosomal DNA, from its end to the middle of the dyad axis. Using fluorescence correlation spectroscopy (FCS), we have established the position dependent rewrapping rates for nucleosomes. We have also used Monte Carlo simulation methods to analyze the applicability of FRET fluctuation spectroscopy towards conformational dynamics, specifically motivated by nucleosome dynamics. Another important conformational change that is involved in cellular processes is the disassembly of nucleosome into its constituent particles. The exact pathway adopted by nucleosomes is still not clear. We used dual color fluorescence correlation spectroscopy to study the intermediates during nucleosome disassembly induced by changing ionic strength. Studying the nature of nucleosome conformational change and the kinetics is very important in understanding gene expression. The results from this thesis give a quantitative description to the basic unit of the chromatin.
ContributorsGurunathan, Kaushik (Author) / Levitus, Marcia (Thesis advisor) / Lindsay, Stuart (Committee member) / Woodbury, Neal (Committee member) / Yan, Hao (Committee member) / Arizona State University (Publisher)
Created2011