The advance in transparent electronics requires high-performance transparent conducting oxide materials. The microscopic properties of these materials are sensitive to the presence of defects and interfaces and thus fundamental understanding is required for materials engineering. In this thesis, first principles density functional theory is used to investigate the possibility of tuning the structural, electronic and magnetic properties of tin oxide by means of defects and interfaces. Our aim is to reveal unique properties and the parameters to control them as well as to explain the origin of unique phenomena in oxide materials. The stability of native defect in tin monoxide (SnO) under strain is investigated using formation energy calculations. We find that the conductivity (which is controlled by native defects) can be switched from p-type to either n-type or undoped semiconducting by means of applied pressure. We then target inducing magnetism in SnO by 3d transition metal doping. We propose that V doping is efficient to realize spin polarization at high temperature. We discuss different tin oxide interfaces. Metallic states are found to form at the SnO/SnO2 interface with electronic properties that depend on the interface terminations. The origin of these states is explained in terms of charge transfer caused by chemical bonding and band alignment. For the SnO/SnO2 heterostructure, we observe the formation of a two dimensional hole gas at the interface, which is surprising as it cannot be explained by the standard polar catastrophe model. Thus, we propose a charge density discontinuity model to explain our results. The model can be generalized to other polar-polar interfaces. Motivated by technological applications, the electronic and structural properties of the MgO (100)/SnO2 (110) interface are investigated. Depending on the interface termination, we observe the formation of a two dimensional electron gas or spin polarized hole gas. Aiming to identify further key parameters, we examine O deficient LaAlO3/SrTiO3 (110) and (001) superlattices under hydrostatic pressure. Presence of O vacancies results in formation of a two-dimensional electron gas, for which we observe a distinct spatial pattern of carrier density that depends strongly on the amount of applied pressure.

The intermittent nature of several sustainable energy sources such as solar and wind energy has ignited the demand of electrochemical energy storage devices in the form of batteries and electrochemical capacitors. The future generation of electrochemical capacitors will in large part depend on the use of pseudocapacitive materials in one or both electrodes. Developing pseudocapacitors to have both high energy and power density is crucial for future energy storage systems. This dissertation evaluates two different material systems to achieve high energy density pseudocapacitive energy storage. This research presents the successful preparation and application of ternary NiCo2S4, which is based on the surface redox mechanism, in the area of pseudocapacitive energy storage. Attention has been paid to understanding its basic physical properties which can impact its electrochemical behavior. Well-defined single- and double-shell NiCo2S4 hollow spheres were fabricated for pseudocapacitor applications, showing much improved electrochemical storage performance with good energy and power densities, as well as excellent cycling stability. To overcome the complexity of the preparation methods of NiCo2S4 nanostructures, a one-step approach was developed for the first time. Asymmetric pseudocapacitors using NiCo2S4 as cathode and graphene as anode were also fabricated to extend the operation voltage in aqueous electrolyte, and thus enhance the overall capacity of the cells. Furthermore, high-performance on-chip pseudocapacitive energy storage was demonstrated using NiCo2S4 as electrochemically active materials. This dissertation also involves another material system, intercalation pseudocapacitive VO2 (B), that displays a different charge storage mechanism from NiCo2S4. By constructing high-quality, atomically-thin two-dimensional (2D) VO2 (B) sheets using a general monomer-assisted approach, we demonstrate that a rational design of atomically thin, 2D nanostructures of atypically layered systems can greatly lower the interaction energy and Li+ diffusion barrier, and it can completely suppress the crystal transformation during the charge-discharge process. As a result, we have successfully enabled the kinetically sluggish step to proceed at room temperature. We show that even at charge-discharge rates as fast as 100C (36 s), these 2D electrodes still offer a high capacity of 140 mAh g-1 due to the rapid Li+ ion diffusion in these 2D sheets. These results discussed in this part conclusively show that the ultrathin 2D geometry of atypically layered or non-layered materials could lead to significantly enhanced pseudocapacitive performance.

The purpose of this study was: (1) to find the effect of temperature on the wet oxidation of chalcopyrite, pyrite, and copper sulfide over the biological and nonbiological range; (2) to determine the influence of ferrous and ferric iron and free oxygen(air) on the oxidation. The sulfide minerals studied were oxidized over a range of temperatures between 25° to 75° C. The optimum biological oxidation occurred near 35° C. The nonbiological oxidation was very slow at low temperatures but increased with increasing temperature. The effect of solutions used in leaching the various sulfides over the temperature range differred. A synthetic nutrient solution, containing only a source of phosphate and nitrogen, was more effective on the biological oxidation of pyrite than on copper sulfide at the optimum temperature. Tailings water, obtained from Bingham Canyon, Utah, was more effective on chalcopyrite over a long period of time than the synthetic nutrient. Ten times more chalcopyrite was oxidized at 70° C. than at 55° C. in a dilute solution of sulfuric acid. A dilute solution of ferrous sulfate had very little effect on the oxidation of the sulfides. Oxygen and ferric iron in oxidized tailings water were shown to affect the oxidation of chalcopyrite at 65° C. The ferric iron was reduced. In an atmosphere of nitrogen, ferrous iron in fresh tailings water was inactive on the oxidation of chalcopyrite. Oxygen is the primary oxidizing agent in the biological and nonbiological oxidation of sulfide minerals in the leaching process.

archives@tulane.edu / 1 / Madhu Sudan Gaire

Nitrogen oxides control the global formation of ozone in the lower atmosphere and influence the much higher levels of ozone formed in areas subjected to photochemical air pollution. As an important member of the nitrogen oxide family, N02 plays a significant role in serving as the only known source of ozone (through photolysis) in the lower atmosphere and as sink for HO via the formation of nitric acid. Ozone can be destroyed by reaction with another member of the nitrogen oxide family, nitric oxide (NO), to reform N02. This cycle between NO, N02 and 03 is known as the NOx-03 photostationary state (PSS). Imbalances in this cycle have been used to calculate ambient levels of oxidants (such as R02 and H02) responsible for ozone production. Consequently, accurate N02 measurements are critical to making meaningful measurements of the imbalances in the NOx-03 photostationary states (PSS). A low pressure laser-excited fluorescence technique (FAGE) for the direct determination of atmospheric N02 has been developed. This technique has been explored with both a Nd-YAG laser (1.4 W, 532nm, 30Hz) and a Cu-vapor (1.2 W, 511nm, 5.6kHz) laser. The detection limits for these instruments, under laboratory conditions and a signal collection time of 20s (lOs each signal and background), have been determined to be 450 and 350pptv N02, respectively. In these systems, the background was measured by chemically reducing N02 with FeS04°7H20. Ambient measurements of the NOx-03 photostationary state (PSS) were undertaken on a rooftop monitoring site in downtown Portland, Oregon. N02 was monitored with the Cu-vapor system. Nitric oxide and ozone were monitored with standard instruments. Data for three days in 1990 are presented. Overall these data sets clearly show that despite daily changes in concentration of NO, N02 and 0 3 of factors of 4-10 each, the PSS remains relatively constant to within -50%. This is in itself strong confIrmation of the primary importance of the NOx-03 photo stationary state in controlling the concentrations of these species at these levels. In addition, these experiments also serve to demonstrate that the monitoring instruments, including FAGE-N02, are not subject to serious interferences or artifacts at these concentration levels.

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