The behaviour of surface plasmon polaritons (SPPs) in nanoscale geometries is studied using numerical methods supported by theory and experiment. First, we derive the behaviour of SPPs at graded metal-dielectric interfaces, including dispersion relations, field profiles, propagation velocities, losses, and cutoff wavelength. Numerical simulations show excellent agreement with analytic solutions. In the second part of the thesis we design hybrid vanadium dioxide-plasmonic based absorption switches. The switches are designed and optimized using optical, electrical and thermal simulations. 5 $\mu$m switch designs have extinction ratios exceeding 30 dB and require powers of 10 mW. A switch is fabricated based on the proposed design. A 7 $\mu$m experimental switch reaches 16.4 dB of extinction and requires 64 mW of power, making it one of the most efficient optical switches ever demonstrated in terms of extinction and power consumption. Numerical simulations predict experimental results with a high degree of accuracy.

The behaviour of surface plasmon polaritons (SPPs) in nanoscale geometries is studied using numerical methods supported by theory and experiment. First, we derive the behaviour of SPPs at graded metal-dielectric interfaces, including dispersion relations, field profiles, propagation velocities, losses, and cutoff wavelength. Numerical simulations show excellent agreement with analytic solutions. In the second part of the thesis we design hybrid vanadium dioxide-plasmonic based absorption switches. The switches are designed and optimized using optical, electrical and thermal simulations. 5 $\mu$m switch designs have extinction ratios exceeding 30 dB and require powers of 10 mW. A switch is fabricated based on the proposed design. A 7 $\mu$m experimental switch reaches 16.4 dB of extinction and requires 64 mW of power, making it one of the most efficient optical switches ever demonstrated in terms of extinction and power consumption. Numerical simulations predict experimental results with a high degree of accuracy.

No description available.

The thin films of oxide xerogels and bronzes and molecular oxide xerogels and bronzes of vanadium compounds were synthesized by sol-gel technology method. The chemical composition of mentioned compounds was investigated using XPS method in order to determine the valence of metal ions. It is shown that it is possible to produce the thin films of vanadium oxide bronzes using simple methods. The possibility to use vanadium-ammonium oxide hydrated compounds as materials for producing the ammonium sensors is shown in the dissertation. / Šiame darbe panaudojant zolis-gelis technologiją, susintetinti vanadžio junginių oksidinių kserogelių ir bronzos bei molekulinių oksidinių kserogelių ir bronzų plonieji sluoksniai. Visų minėtų medžiagų cheminė sudėtis ištirta Rentgeno fotoelektronų spektroskopijos metodu, siekiant nustatyti metalų jonų valentines būsenas. Panaudojant zolis-gelis technologiją, galima gana paprastais metodais, nenaudojant sudėtingos technologinės įrangos, gaminti vanadžio oksidinių bronzų plonuosius sluoksnius. Vanadžio amonio hidratuoti oksidiniai junginiai gali būti naudojami kaip medžiagos amoniako dujų jutikliams gaminti.

Electrochemical capacitors, now often termed supercapacitors, are high power electrochemical energy storage devices that complement or replace high power batteries in applications ranging from wind turbines to hybrid engines to uninterruptable power supplies to electronic devices. My dissertation explores the applications of relatively uncommon techniques for both supercapacitor material syntheses and gaining better mechanistic understanding of factors impacting electrochemical performance of supercapacitors. From fundamental ion electroadsorption studies made possible by using small angle neutron scattering (SANS), to the systematic investigations of coating thickness and microstructure in metal oxide / carbon nanocomposite electrodes realized through the novel use of the atomic layer deposition (ALD) technique, new avenues of material characterization and fabrication have been studied. In this dissertation I first present the motivation to expand the knowledge of supercapacitor science and technology, and follow with an in-depth literature review of the state of the art. The literature review covers different types of supercapacitors, the materials used in the construction of commercial and exploratory devices, an exploration of the numerous factors which affect supercapacitor performance, and an overview of relevant materials synthesis and characterization techniques The technical objectives for the work performed in this dissertation are then presented, followed by the contributions that I made in this field in my two primary research thrusts: advances to the understanding of ion electroadsorption theory in both aqueous and organic electrolytes through the development of a SANS-based methodology, and advances to metal-oxide carbon nanocomposites as electrodes through the use of ALD. The understanding of ion electro-adsorption on the surface of microporous (pores < 2 nm) solids is largely hindered by the lack of experimental techniques capable of identifying the sites of ion adsorption and the concentration of ions at the nanoscale. In the first research thrust of my dissertation, I harness the high penetrating power and sensitivity of neutron scattering to isotope substitution to directly observe changes in the ion concentration as a function of the applied potential and the pore size. I have conducted initial studies in selected aqueous and organic electrolytes and outlined the guidelines for conducting such experiments for the broad range of electrode-ions-solvent combinations. I unambiguously demonstrate that depending on the solvent properties and the solvent-pore wall interactions, either enhanced or reduced ion electro-adsorption may take place in sub-nanometer pores. More importantly, for the first time I demonstrate the route to identify the critical pore size below which either enhanced or reduced electrosorption of ions takes place. My studies experimentally demonstrate that poor electrolyte wetting in the smallest pores may indeed limit device performance. The proposed methodology opens new avenues for systematic in-situ studies of complex structure-property relationships governing adsorption of ions under applied potential, critical for rational optimization of device performance. In addition to enhancing our understanding of ion sorption, there is a critical need to develop novel supercapacitor electrode materials with improved high-energy and high-power characteristics. The formation of carbon-transition metal oxide nanocomposites may offer unique benefits for such applications. Broadly available transition metal oxides, such as vanadium oxide, offer high ion storage capabilities due to the broad range of their oxidation states, but suffer from high resistivities. Carbon nanomaterials, such as carbon nanotubes (CNT), in contrast are not capable to store high ion content, but offer high and readily accessible surface area and high electrical conductivity. In the second research thrust of my thesis, by exploiting the ability of atomic layer deposition (ALD) to produce uniform coatings of metal oxides on CNT electrodes, I demonstrated an effective way to produce high power supercapacitor electrodes with ultra-high energy capability. The electrodes I developed showed stable performance with excellent capacitance retention at high current densities and sweep rates. Electrochemical performance of the oxide layers were found to strongly depend on the coating thickness. Decreasing the vanadium oxide coating thickness to ~10 nm resulted in some of the highest values of capacitance reported to date (~1550 F·g⁻¹VOx at 1 A·g⁻¹ current density). Similar methodology was utilized for the deposition of thin vanadium oxide coatings on other substrates, such as aluminum (Al) nanowires. In this case the VOₓ coated Al nanowire electrodes with 30-50% of the pore volume available for electrolyte access show volumetric capacitance of 1390-1950 F cc⁻¹, which exceeds the volumetric capacitance of porous carbons and many carbon-metal oxide composites by more than an order of magnitude. These results indicated the importance of electrode uniformity and precise control over conformity and thickness for the optimization of supercapacitor electrodes.

No description available.

The Vanadium bromide (V/Br) flow cell employs the Br3-/Br- couple in the positive and the V(II)/V(III) couple in the negative half cell. One major issue of this flow cell is bromine gas formation in the positive half cell during charging which results from the low solubility of bromine in aqueous solutions. Bromine complexing agents previously used in the zinc-bromine fuel cell were evaluated for their applicability in V/Br flow cell electrolytes. Three quaternary ammonium bromides: N-ethyl-N-methyl-morpholinium bromide (MEM), N-ethyl-N-methyl-pyrrolidinium bromide (MEP) and Tetra-butyl ammonium bromide (TBA) were studied. It is known that aqueous bromine reacts with quaternary ammonium bromides to form an immiscible organic phase. Depending on the number of quaternary ammonium bromides used and the environmental temperature, the second phase formed will either be solid or liquid. As any solid formation would interrupt the flow cell operation, potential formation of such kind has to be eliminated. Stability tests of simulated V/Br electrolyte with added quaternary ammonium bromides were carried out at 11, 25 and 40 oC. In the absence of bromine, the addition of MEM, MEP and TBA were found to be stable in V/Br electrolytes. However, in the presence of bromine, solid formation was observed in the bromine rich organic phase when the V/Br electrolyte contained a single quaternary ammonium bromide (QBr) compound. For V/Br electrolytes with binary or ternary QBr mixtures containing TBA, the presence of bromine caused a viscous polybromide phase to form at room temperature and the release of bromine gas at higher temperature. Only a binary mixture of MEM and MEP formed a stable liquid organic phase between 11 ?? 40 oC. In this study it was found that V/Br electrolytes containing a binary QBr mixture (0.75M) of MEM and MEP gave the best combination that formed an orange oily layer in the presence of bromine without solidification between 11 ?? 40oC. Furthermore, it was found that samples of V/Br electrolytes containing a ternary QBr mixture, are less effective in bromine capturing if the total QBr concentration was less than 1 M at 40oC, where bromine gas evolution was observed. From electrochemical studies of V3+/V2+, it was found that the addition of MEM and MEP had a minimal effect on the formal potential of the V3+/V2+ couple, the V2+/V3+ transfer coefficient and the diffusion coefficient of V3+. Therefore, MEM and MEP can be added to the negative half-cell of a V/Br flow cell without major interference From linear sweep voltammetry, the kinetics of the Br-/Br3- redox couple was found to be mass transfer controlled. After the addition of MEM and MEP mixture, the exchange current density was found to decrease from 0.013 Acm-2 to 0.01 Acm-2. On the other hand the transfer coefficient before and after MEM and MEP addition was found to be 0.5 and 0.44 respectively. Since the kinetic parameters were not significantly affected by the addition of MEM and MEP mixture, they can be added to the positive half-cell of the V/Br flow cell as bromine complexing agents. The electrochemical studies of both V3+/V2+ and Br-/Br3- showed the addition of MEM and MEP has minimal interference with the redox reactions of the vanadium bromide flow cell. This thesis also investigated the effect of MEM and MEP addition on the cell performance of a lab scale V/Br flow cell using two different membranes (ChiNaf and VF11). Flow cell performance for 2 M V3.7+ + 0.19 M MEM + 0.56 M MEP electrolytes utilising ChiNaf membrane at 10 mAcm-2 produced an energy efficiency of 59%, and this decreased to 43% after 15 cycles. For the static cell utilising VF11 membrane, the addition of MEM and MEP reduced the energy efficiency from 59.7% to 43.4%. It is believed that this is caused by the mass transfer controlled Br-/Br3- couple in the complexed positive half-cell solution. Therefore, uniformity between the organic and aqueous phase is important for flow cells utilising electrolytes with MEM and MEP. Finally, the polarization resistance of a lab scale V/Br flow cell utilising ChiNaf membrane and 2 M V3.7+ electrolytes was found to be slightly higher during cell charging (3.9 cm2) than during the discharge process (3.6 cm2), which is opposed to that in the all-vanadium redox cell.

Techn. Universiẗat, Diss., 2007--Darmstadt.

Thesis (Ph. D.)--Mechanical Engineering, Georgia Institute of Technology, 2008. / Committee Chair: David. L. McDowell; Committee Member: Min Zhou; Committee Member: Naresh N. Thadhani; Committee Member: Rami M. Haj-Ali; Committee Member: Richard W. Neu.

Thesis (PhD.(Immunology)--Faculty of Health Sciences)-University of Pretoria, 2007. / Includes bibliographical references.