There is no abstract available for this dissertation.

Chiral molecules, which exist under enantiomers with non-mirror-symmetrical structures, have been the subject of intense research for their linear and nonlinear optical activities. Cysteine is such a chiral amino acid found as a building block of proteins throughout human bodies. Second harmonic generation (SHG) has been considered to investigate chiral molecules. SHG from metallic nanoparticles is promising for nanoplasmonics and photonic nanodevice applications. Therefore, it’s desirable to combine and study nonlinear properties due to both chirality and metallic nanoparticles, and help developing an alternatively optical diagnostic of chiral molecules. Our experiments are carried out with the FemtoFiber Scientific FFS laser system. SHG of silver nanoparticles (Ag NPs) modified by either L-Cysteine (L-C) or D-Cysteine (D-C) is observed, where L-Cysteine and D-Cysteine are a pair of enantiomers. Ag NPs are deposited through Vacuum Thermal Evaporation, controlled under different deposition thicknesses. UV-Vis/IR spectra and AFM are used to characterize Ag NPs under different conditions. Transmitted SHG measurements dependent on incidence are recorded with standard lock-in techniques. Deposition thickness of vacuum thermal evaporation plays an important role in forming diverse Ag NPs, which strongly imparts the intensity of SHG. Second harmonic intensity as a function of the incident angle presents similar results for Ag NPs with or without L-Cysteine or D-Cysteine modification, in the output of p- and s-polarization. However, we monitor reversed rotation difference in second harmonic intensities at linearly +45° and -45° polarization for L-C/Ag NPs and D-C/Ag NPs, while there’s no difference at linearly +45° and -45° polarization for Ag NPs alone. This optical rotation difference in SHG is termed as SHG-ORD. Also, for second harmonic light fixed at p-polarization, L-C/Ag NPs and D-C/Ag NPs exhibit a reversely net difference for SHG excited by right and left circular polarization, which is termed as SHG-CD. Experiments on SHG-ORD of chiral-modified Ag NPs by a mixture of L-Cysteine and D-Cysteine further help verifying the existence of chirality in chiral-modified Ag NPs. As a conclusion, SHG efficiently probed and distinguished L-Cysteine from D-Cysteine in chiral-modified Ag NPs. / Thesis (Master, Physics, Engineering Physics and Astronomy) -- Queen's University, 2013-09-29 21:27:23.112

Bionanotechnology is an intersection between biology and nanotechnology, a field in which novel applications for very small materials are being realised at an alarming rate. Nanoparticles have 3 dimensions that can be measured in nanometers, their small size conferring upon them different properties from individual atoms or the bulk material. The interactions between these unique materials and microorganisms are often toxic, thus have been exploited for antimicrobial applications. However, there is a considerable paucity of data for the underlying molecular mechanisms. This study has been carried out to investigate the interactions that occur between nanoparticles and bacteria with the objective of identifying these toxicological mechanisms and novel nanoparticle effects, using the model Gram negative organism Escherichia coli K12. This study has identified metal nanoparticles that are a superior vehicle for the delivery of toxic metal ions to E. coli. The nanoparticles associate with the bacterial surface, but do not cross the cell wall. They then dissolve, releasing a concentration of metal ions that accumulate at the bacterial-nanoparticle interface, enhancing the antibacterial efficacy compared to the concentration of metal ions in the bulk solution phase. Measurement of the whole transcriptome response to silver nanoparticles in comparison to the silver ion indicates that the different modes of ion delivery may induce a differential stress response. Moreover, this data identifies molecular mechanisms that are involved in the toxicity of this metal that is now becoming increasingly prevalent in society. The dissolution based toxic effects of zinc oxide nanoparticles are augmented by an interaction with ultra-violet light, offering an alternative mode for nanoparticle toxicity.

The handling of metallic nanoparticles often requires their dispersion into several polar and nonpolar solvents. Solid-phase stages or polymer-based ligands are commonly required to complete the transfer. The construction of a thiol ligand based in oleic acid, and its ability to efficiently assist in gold and silver nanoparticle aqueous-organic phase transfer is reported. After the transfer, the particles are completely dispersed in an organic solvent, preserving their diameter and morphology, as confirmed by ultraviolet-visible spectroscopy and scanning transmission electron micrographs.

High-temperature electrical- and morphological-stability of interconnect is critical for electronic systems based on wide band gap (WBG) semiconductors. In this context, the thermal stability of both Ag and Cu films with Ta and TaN films as diffusion barriers and/or surface-capping layers at high temperatures up to 800 oC is investigated in this thesis. The investigation of un-capped Ag films with either Ta or TaN diffusion barrier layers shows electrical stability upon annealing up to 600 °C. Degradation occurs above 600 °C mainly as a result of void formation and Ag agglomeration. Sandwiching Ag films between Ta and/or TaN layers is found to electrically and morphologically stabilize the Ag metallization up to 800 °C. The barrier layer plays a key role; the β-to-α phase transition in the underlying Ta barrier layer is identified as the major cause for the morphological instability of the film above 600 °C. This phase transition can be avoided using a stacked Ta/TaN barrier. Furthermore, no observable Ta diffusion in Ag films is found. Copper films with a Ta diffusion barrier show clearly different behaviors. In the Cu/Ta sample, Ta starts to diffuse up to the surface via fast-diffusing grain boundaries (GBs) after annealing at 500 °C. The activation energy for the GB diffusion is 1.0+0.3 eV. Un-capped Cu is electrically stable up to 800 °C. An appreciable increase in sheet resistance occurs above 600 °C for the asymmetric combinations Ta/Cu/TaN and TaN/Cu/Ta. This degradation is closely related to a substantial diffusion of Ta across the Cu film and on to the TaN layer, where Ta1+xN forms. The symmetrical combinations Ta/Cu/Ta and TaN/Cu/TaN show only small changes in sheet resistance even after annealing at 800 °C. No Ta diffusion can be found in the Ta/Cu/Ta and TaN/Cu/TaN stacks. Finally, the influence of barrier and cap, their interfaces to Cu and Ta diffusion and segregation in the Cu GBs on electromigration is studied. Our preliminary results with the TaN/Cu/Ta and TaN/Cu/TaN structures report a 2-fold higher activation energy and a 10-fold longer lifetime for the former, thus confirming an important role of the interface between Cu and the cap and/or barrier.

Bacteria may live in harsh environments where they face changing and new conditions. Therefore, the ability to maintain homeostasis in cells may be vital for survival. Transition metals such as iron, zinc, and copper are essential nutrients for cell survival, but become toxic if in excess amount. In order to survive, bacteria have developed defensive mechanisms to protect themselves. Copper and silver levels need to be carefully maintained within cells to balance cellular needs with potential toxicity. This dissertation focuses on the Cus copper and silver efflux system in E. coli. The E. coli cus system is composed of two divergently transcribed operons, cusCFBA and cusRS. The cusCFBA genes encode for a tripartite metal efflux pump CusCBA and a metallochaperone CusF. The cusRS genes encode a two-component system CusS-CusR that regulates the expression of the cusCFBA genes in response to elevated levels of copper or silver in the periplasm. The histidine kinase CusS senses and binds to metals on its periplasmic sensor domain and transduces signal into the cytoplasm to further communicate with its cognate response regulator CusR through histidyl-aspartyl phosphotransfer event. CusR then outputs cellular response by activating the upregulation of the cusCFBA genes, which then turn on the CusCBA efflux pump to eliminate excess copper or silver in the periplasm. While bacterial two-component systems have been widely studied, the mechanisms of ligand-induced signal transduction by histidine kinases remain unclear. It is now known that cusS is essential for copper and silver resistance, and CusS directly binds metal ions in the periplasmic sensor domain and dimerizes upon metal binding. Thus, the goal of this research is to characterize the metal binding properties in the sensor domain, and to elucidate the signal transduction and autophosphorylation mechanisms of CusS upon metal binding. The data from this work reveal that there are two distinct metal binding sites, interface and internal binding sites, in the sensor domain of CusS, and the interface binding site is functionally more important in metal resistance in E. coli. Furthermore, metal-induced dimerization through the interface metal binding site plays an important role in CusS kinase activity. Together, these findings aid in our understanding of the molecular details in metal binding within the sensor domain of CusS. Based on these data, we propose a model for the signal transduction mechanism and histidine phosphorylation mechanism of the histidine kinase CusS.

Porous silicon dioxide thin films were produced via dip-coating and doped with Ag+ by adding AgNO3 to the dipping solution. Nanoparticles were formed within the pores of these films by UV exposure. Nanoparticle formation was confirmed by UV-visible spectroscopy and Transmission Electron Microscopy (TEM). Conductive Atomic Force Microscopy (CAFM) showed that the conductivity of the films decreased upon exposure to UV. This decrease in the conductivity is most likely due to the clustering of charge carriers. Initially, Ag+ ions are attached to negatively charged pore walls in a dense packing network. Upon UV exposure (125 mW @ 266 nm), the Ag+ ions are reduced to Ag metal and agglomerate to form clusters. The agglomeration creates gaps in the film that decrease its conductivity. This ability to tune film conductivity was used to create insulating patterns within conducting films. A calibration mask was placed over the films during UV exposure, and exposed regions with a minimum width of ~2 μm were detected as depressions with insulating behavior. The fabrication of photonic and plasmonic devices is being explored using this method.

Predicting and verifying the tunable optical properties of metal nanostructures is central to designing materials optimized for specific applications. Chemically- deposited nanostructures have been well-studied near the percolation threshold, but at lower surface coverages they exhibit sample-to-sample variations in the optical response. We identify how these variations are driven by the high variability in the particle size distribution in a particular surface coverage range. We then explore film- coupled nanoparticle systems consisting of a silver nanoparticle, thin dielectric spacer layer, and flat silver film, to enable tuning toward the blue and green parts of the spectrum. We use the boundary element method to visualize charge distributions of various resonances. We fabricate samples using thermal evaporation and spin coating methods, and use polarized reflectance spectroscopy to measure their optical response at an ensemble level. We achieve a 532nm resonance for 80nm silver nanoparticles on 13nm PMMA spacers and 100nm silver thin films. The resulting design is a candidate for enhancing fluorescence in a new spectral range. This dissertation includes previously unpublished co-authored material.

Submitted by PPG Engenharia e Tecnologia de Materiais (engenharia.pg.materiais@pucrs.br) on 2018-06-28T19:58:26Z No. of bitstreams: 1 FICHA_CATALOGR?FICA_EMBUTIDA_Disserta??o Cristiano_Jaeger Stradolini_Processo Poliol.pdf: 3080490 bytes, checksum: 6539be3aad396dd1f8b30cd3389b1469 (MD5) / Approved for entry into archive by Sheila Dias (sheila.dias@pucrs.br) on 2018-07-06T13:07:04Z (GMT) No. of bitstreams: 1 FICHA_CATALOGR?FICA_EMBUTIDA_Disserta??o Cristiano_Jaeger Stradolini_Processo Poliol.pdf: 3080490 bytes, checksum: 6539be3aad396dd1f8b30cd3389b1469 (MD5) / Made available in DSpace on 2018-07-06T13:12:44Z (GMT). No. of bitstreams: 1 FICHA_CATALOGR?FICA_EMBUTIDA_Disserta??o Cristiano_Jaeger Stradolini_Processo Poliol.pdf: 3080490 bytes, checksum: 6539be3aad396dd1f8b30cd3389b1469 (MD5) Previous issue date: 2018-03-22 / Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior - CAPES / During the past few years, nanosized noble metals have attracted much attention due to their unique electrical and physical properties. Among them, silver has been the subject of several studies, by having the highest electrical and thermal conductivity between all metals. For that reason, its one-dimensional nanometric structure (nanowires) has been receiving a lot of attention, due to its potential in the manufacture of devices that offer good electrical conduction and optical transparency. There are several methods of synthesis for the production of these silver nanowires, however the most widely used is the polyol process, due to its simplicity and low cost. Several studies show the influence of different parameters of the polyol process (reaction time, temperature and etc.) on the final morphology of the nanowires. Thus, a well-defined protocol of good practice for obtaining long and thin silver nanowires is required. The main objective of this work is the development of a low cost protocol capable of generating nanowires with great lengths by modifying the polyol process parameters. Variations were also performed in the method of addition of the main synthesis reagent, silver nitrate, and its influence on the final morphology of the silver nanowires was studied. In this work, by using the polyol process, nanowires up to 40 ?m in length were reported, demonstrating the effectiveness of the developed technique and conclusions about the final results were presented. / Ao decorrer dos ?ltimos anos, metais nobres na escala nanom?trica t?m atra?do muita aten??o, devido as suas propriedades el?tricas e f?sicas ?nicas. Dentre eles, a prata vem sendo alvo de diversos estudos, por possuir a maior condutividade el?trica e t?rmica entre todos os metais. Por conta disto, sua estrutura nanom?trica unidimensional (nanofios) vem recebendo muita aten??o, pelo seu potencial na fabrica??o de dispositivos que exijam alta condutividade el?trica e transpar?ncia ?ptica. Atualmente, existem diversos m?todos de s?nteses para a produ??o destes nanofios de prata, por?m o mais utilizado ? o processo poliol, por ser simples e de baixo custo. Diversos estudos demonstram a influ?ncia de diferentes par?metros do processo poliol (tempo de rea??o, temperatura e etc.) sobre a morfologia final dos nanofios. Assim, se faz necess?rio um protocolo bem definido de boas pr?ticas para a obten??o de fios longos e finos. O principal objetivo deste trabalho ? o desenvolvimento de um protocolo de baixo custo capaz de gerar nanofios com grandes comprimentos, atrav?s de altera??es nas vari?veis do processo poliol, como, por exemplo, varia??es no m?todo de adi??o do principal reagente da s?ntese, o nitrato de prata. Foi estudada a sua influ?ncia na morfologia final dos nanofios. Neste trabalho, os resultados finais apresentaram que nanofios de at? 40 ?m de comprimento foram produzidos pelo processo poliol, demonstrando a efic?cia da t?cnica desenvolvida e foram apresentadas as conclus?es acerca dos resultados atingidos.

This thesis studies networks of silver nanowires as a transparent conducting electrode material and presents an investigation into the relationship between electrical and optical properties in the networks. The work focusses on two main aspects: the production of networks via different deposition methods; and the development of a predictive model based on theory that relates the sheet resistance to the optical transmittance. The deposition methods of drop-casting, bar-coating and spray-coating are used to create networks and the randomness of these networks is compared using image analysis in ImageJ, a public domain image processing program, and Wolfram Mathematica, a computer algebra program. It is determined that spray-coating results in the most random networks, therefore all subsequent experiments are carried out using this as the deposition method. Annealing condition tests are carried out on the nanowire networks to determine the optimal annealing conditions required to burn off poly(vinyl pyrrolidone) (PVP) remaining from the nanowire synthesis process and sinter the nanowire junctions to improve network conductivity. The sheet resistances and optical transmittances of the networks are measured and compared to networks created by other research groups. It is found that the networks created in this study exhibited similar optical and electrical properties to those in the literature, obtaining Rs = 100 Ω/sq for T = 81%.The developed model is based on theory and relates the sheet resistance to the optical transmittance using only the length and width of the nanowires used in the network and the mean network coverage as variables. The model can be used to predict the properties of a network if these factors are known. The model is compared with experimental data both from this study and from the literature, along with simulated data from the literature that was obtained by Monte Carlo methods. It is shown that there is an excellent fit between the model and all data that it is compared with. It is demonstrated that < 1% of the network coverage is greater than 2 for typical nanowire networks, proving that the networks are two-dimensional and therefore do not require a bulk regime to describe the relationship, as has been suggested in prior work.