Browsing by Subject "Silver"
Now showing 1 - 9 of 9
Results Per Page
Sort Options
Item Determination of silver using cyclic epithermal neutron activation analysis(2010-05) Pun, Tin-Hei; Landsberger, Sheldon; Biegalski, StevenA fast pneumatic transfer facility was installed at the Nuclear Engineering Teaching Laboratory (NETL) of the University of Texas at Austin for the purpose of cyclic thermal and epithermal neutron activation analysis. In this work efforts were focused on the evaluation of cyclic epithermal neutron activation analysis (CENAA). Various NIST and CANMET certified materials were analyzed by the system. Experiment results showed 110Ag as one of the isotopes favored by the system. Thus, the system was put into practical application for identifying silver concentration in the Arctic atmospheres in air filters collected in 2009, and traces in metallic ores Comparison of silver concentrations via CENAA with the CANMET certified reference materials gave very good results.Item Enzymatic inhibition-based biosensing on nitrogen-doped carbon nanotube electrodes(2015-05) Rust, Ian Matthias; Stevenson, Keith J.; Webb, Lauren JWhile previous work has demonstrated the effectiveness of nitrogen-doped carbon nanotubes (N-CNTs) as biogenic electrode materials in first- and second-generation biosensors, this thesis primarily explores enzymatic inhibition-based biosensing schemes on N-CNT electrodes. This type of scheme enables the detection of enzymatic inhibitors, as opposed to enzymatic substrates, making these inhibition-based biosensors much more suitable for the monitoring of environmental pollutants. Presented in this thesis is a biosensor which couples N-CNTs with glucose oxidase (GOx) through spontaneous physical adsorption for the highly sensitive detection of aqueous silver ions. Included is a thorough discussion of the parameters that affect response time as well the biosensor’s aptitude for repeated use. A later chapter presents initial work towards the inhibition-based detection of sucralose, a relatively new environmental pollutant. A bi-enzymatic approach is explored, in which both GOx and invertase are immobilized on an N-CNT modified electrode. Finally, shifting focus from inhibition-schemes, the last remaining chapter investigates the coupling of CNTs and N-CNTs with methylene green (MG), a redox mediator used in second-generation biosensors based on NADH oxidation. Common coupling techniques are examined for their effectiveness in decreasing the overpotential required for NADH oxidation.Item Film deposition and mechanical properties of silver produced by impaction of nanoparticles(2012-12) Noiseau, Guillaume Jack Nicolas; Kovar, Desiderio; Becker, Michael FNanocrystalline films are promising in various fields such as microelectronics. Low temperature deposition techniques are desirable since they would enable the use of new substrates that are temperature sensitive, leading to a wide range of new applications. This thesis explores nanocrystalline silver film deposition by impacting nanoparticles (NP) onto a substrate, a technique that enables low process temperatures. This work aims at better understanding the physical parameters governing the sticking probability of NP upon impaction. To achieve this, various substrate materials have been used (metallic and non metallic) and the influence of the impacted substrate temperature has been studied, among other experiments. These parameters showed a significant influence on the collection efficiency of NPs. These experimental results are analyzed in light of published computer simulations studies predicting the behavior of impacting NP to deposit nanostructured films. Secondly, a study of the mechanical properties of the deposited films has been attempted. Compression tests have been carried out varying the applied load, loading time and process temperature. The produced films are nanocrystalline and porous (~70% relative density). Densification has been observed even at room temperature, and the goal of this study is to understand which mechanisms cause the densification to occur. The experimental densification data are compared with a model describing the densification of microparticles compacts by hot pressing that has been adapted to nanocrystalline silver, and the mechanisms leading to densification are discussed.Item Growth, structure, and chemistry of 1B metal nanoclusters supported on TiO₂(110)(2006) Pillay, Devina; Hwang, Gyeong S.Cu, Ag, and Au nanoclusters dispersed on TiO2(110) surfaces are utilized in a wide variety of applications ranging from microelectronics to heterogeneous catalysis. The unique chemical reactivity of these clusters is largely dependent on their size, shape, spatial distribution, and interfacial interaction with the oxide support. This implies that atomic level control of these properties can offer great opportunities in the development of novel devices based on supported metal nanoclusters. It is therefore necessary to understand how formation and restructuring of these clusters alter their geometric and electronic characteristics. This thesis involves the development of a theoretical foundation for studying the growth, structure, and chemistry of Cu, Ag, and Au on TiO2(110) surfaces. Using density functional theory calculations, we have identified factors that control the chemical reactivity of these supported metal nanoclusters. First we investigated the electronic and geometric structures of the stoichiometric and reduced rutile TiO2(110) surfaces. Then we examined the surface chemistry of TiO2 towards gaseous CO and O2, as well as the structure and growth of 1B metal nanoclusters on TiO2(110). We also examined how the electronic and geometric properties of mixed metal nanoclusters, CuAun(n≤ 3), differ versus their single metal counterparts, Cum and Aum (m ≤ 4). Finally, we considered CO oxidation reactions on TiO2(110)-supported small Au clusters. While current experimental techniques are limited to providing complementary atomic-level real space information, first principles-based atomic level simulations greatly contribute to elucidating the fundamental behavior and properties of Cu, Ag, and Au nanoclusters on TiO2(110). First principles modeling has paved the way for new catalyst development by investigating how the geometric, electronic, and chemical properties of TiO2-supported 1B metal nanoclusters vary with surface defects, adsorbates, and metal dopants before valuable time and manpower is invested in experimental synthesis and characterization.Item Localized surface plasmon resonance spectroscopy of gold and silver nanoparticles and plasmon enhanced fluorescence(2011-12) Vokac, Elizabeth Anne; Willets, Katherine A.; Brodbelt, Jennifer S.This thesis presents spectroscopic studies of metallic nanoparticle localized surface plasmons and plasmon enhanced fluorescence. We investigated the dielectric sensitivity of silver nanoprisms to an external electric field and gold nanorods to the formation of a self-assembled surface monolayer. Dark field microscopy was used to image plasmonic scattering from single nanoparticles, and a liquid crystal tunable filter was used to construct corresponding spectra. The plasmon resonances of silver nanoprisms displayed both reversible red shifts and irreversible blue shifts along with drastic intensity changes upon exposure to an applied bias. The plasmon resonances of gold nanorods showed sensitivity to the presence of alkanethiol molecules adhered to the particle surface by a moderate red shift. An increase in the effective external dielectric caused a shift toward longer wavelengths. We imaged plasmon enhanced fluorescence in order to optimize experimental parameters for a developing project that can characterize nanoparticle structure on sub-wavelength dimensions. Preliminary controls were performed to account for the effect of O₂ plasma treatment, solvent and alkanethiol monolayer formation on surface plasmon resonances. We found that O₂ plasma treatment for different time intervals did not result in a plasmon shift compared to untreated nanoparticles exposed to N₂; however when exposed to solvent the surface plasmons of the treated particles shifted five times as far toward the red. Interestingly, the solvent effect only resulted in a plasmon shift when the particles were N₂ dried after solvent incubation. Gold nanorods incubated in ethanol showed no wavelength maximum shift in pure solvent over time, but shifted moderately to the red after incubation in a solution of alkanethiol molecules. Conditions for the plasmon enhanced fluorescence study were optimized using a dye conjugate of the same alkanethiol molecule used previously by formation from solution in a monolayer on the gold nanorod surface. The appropriate synthesis for dye functionalization, molecular concentrations, solvents and optical settings were determined.Item Nanostructured Ag produced by LAMA(2007) Albert, André David; Kovar, DesiderioItem Nanostructured Ag produced by LAMA(2007-05) Albert, André David; Kovar, DesiderioItem Size distributions and nonlinear optical enhancement of silver nanoparticles produced by LAM(2011-05) Erickson, Nathan William; Keto, John W.; Becker, Michael; Downer, Michael; Fink, Manfred; Sitz, GregIn this dissertation, I will look into the size distribution of silver nanoparticles produced by laser ablation of microparticles (LAM). I will investigate the role of both pulsed and continuously operating nozzles on the size distribution. In addition, I will examine any deviations from the previously observed log-normal size distribution for silver nanoparticles comparing previous collection techniques involving supersonic jet impaction with a current time of flight mass spectrometer (TOF-MS). These new observations will be made in situ using a Wiley-McLaren TOF-MS with a reflector and multiphoton ionization and will mainly focus on the smaller sized nanoparticles. An introduction to enhancing a second harmonic optically generated signal will also be investigated involving silver nanocomposites while utilizing a polarized crossed-beam femtosecond laser technique.Item Tailoring nanoscale metallic heterostructures with novel quantum properties(2013-05) Sanders, Charlotte E.; Shih, Chih-Kang; Raizen, Mark G.Silver (Ag) is an ideal low-loss platform for plasmonic applications, but from a materials standpoint it presents challenges. Development of plasmonic devices based on Ag thin film has been hindered both by the dificulty of fabricating such film and by its fragility out of vacuum. Silver is non-wetting on semiconducting and insulating substrates, but on certain semiconductors and insulators can adopt a metastable atomically at epitaxial film morphology if it is deposited using the "two-step" growth method. This method consists of deposition at low temperature and annealing to room temperature. However, epitaxial Ag is metastable, and dewets out of vacuum. The mechanisms of dewetting in this system remain little understood. The fragility of Ag film presents a particular problem for the engineering of plasmonic devices, which are predicted to have important industrial applications if robust low-loss platforms can be developed. This dissertation presents two sets of experiments. In the first set, scanning probe techniques and low energy electron microscopy have been used to characterize Ag(111) growth and dewetting on two orientations of silicon (Si), Si(111) and Si(100). These studies reveal that multiple mechanisms contribute to Ag film dewetting. Film stability is observed to increase with thickness, and thickness to play a decisive role in determining dewetting processes. A method has been developed to cap Ag film with germanium (Ge) to stabilize it against dewetting. The second set of experiments consists of optical studies that focus on the plasmonic properties of epitaxial Ag film. Because of the problems posed until now by epitaxial Ag growth and stabilization, research and development in the area of plasmonics has been limited to devices based on rough, thermally evaporated Ag film, which is robust and simple to produce. However, plasmonic damping in such film is higher than in epitaxial film. The optical studies presented here establish that Ag film can now be stabilized sufficiently to allow optical probing and device applications out of vacuum. Furthermore, they demonstrate the superiority of epitaxial Ag film relative to thermally evaporated film as a low-loss platform for plasmonic devices spanning the visible and infrared regimes.