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Thesis (Ph. D.)--University of Wisconsin--Madison, 1970. / 2 folded maps in pocket. Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.

In this thesis, the growth of 2D materials, in particular graphene and FeO2 on crystalline supports, is studied by a multitude of surface-sensitive techniques. The mechanisms of graphene growth in ultra-high vacuum and high Ar pressure are explored, and a simple device for the manufacturing of high-quality, monocrystalline graphene on SiC is described. The electronic and chemical properties of B and N dopants on graphene are characterized by means of STM/AFM with CO-functionalized tips and supported by DFT calculations. The chemical interaction of a probe molecule (FePc) with doped graphene is also investigated. The long-standing controversy of the so-called "biphase" reconstruction of α - Fe2O3(0001) is resolved by the discovery of a complete FeO2 overlayer in this phase. The structure of this overlayer is investigated by means of STM, LEEM and DFT calculations. A thorough description of the routes to obtain single phases over the whole surface of α - Fe2O3(0001) is provided.

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The rise in anthropogenic carbon dioxide in the atmosphere has caused the pursuit of adequate methods to alleviate the resulting strain on the world's ecosystem. A promising strategy is the geological sequestration of carbon dioxide, in which carbon dioxide emitted from large point sources is injected underground for storage. Under storage, carbon dioxide trapped as a carbonate mineral may be stable for geological time periods. Experiments were conducted to test the potential of ferric-bearing minerals to sequester carbon as a ferrous carbonate mineral (siderite). The formation of siderite requires the reduction of ferric ions which may be achieved by the co-injection of H2S or SO2 contaminants with CO2. Both ferrihydrite and hematite nanoparticles were exposed to an aqueous Na2S solution in the presence of supercritical CO2 (scCO2) and were analyzed in situ by attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR). In situ ATR-FTIR indicated that the formation of siderite occurred on the order of minutes for ferrihydrite and hematite nanoparticles. Particles were analyzed post-reaction with X-ray diffraction (XRD) and electron microscopy. XRD results indicated that ferrihydrite reacted completely to form siderite and elemental sulfur after 24 h at 100 °C, while hematite only partially reacted to form siderite and pyrite after 24 h at 70 °C. Additionally, hematite nanoparticles were exposed to H2S and scCO2 in a series of batch reactions, and the reaction products were determined by XRD as a function of CO2 and H2S partial pressures, alkalinity, salinity, time, and temperature. / Chemistry

The influence of sulfate on terrestrial and aquatic ecosystems depends on the mobility of the sulfate anion in soils. This mobility is determined by several factors, one being the types and amounts of soil constituents. In this study, several iron oxide/hydroxide minerals were evaluated for sulfate sorption characteristics.Hematite and goethite were synthesized and positively identified using x-ray diffraction, mossbauer spectroscopy and scanning electron microscopy. Mineral surfaces were characterized using surface area and zero point of charge measurements, infrared spectroscopy and thermal analyses. Neutron activation and x-ray fluorescence were used to look for impurities. Samples were compared to a natural hematite sample and a synthetic jarosite. Sorption experiments, conducted on mineral suspensions in KNO3 media at room temperature, considered the variables time, ionic strength, solid:solution ratio, pH and sulfate concentration. Sorption was initiated by a fast reaction, followed by a longer, slower one which reached an apparent equilibrium in 24 hours. Sorption was unaffected by sol id:solution ratio and decreased with ionic strength at pH 5 for goethite only. Sorption increased with increasing sulfate concentration and decreasing pH. A sorption maximum was reached by a I 1 minerals except synthetic hematite. Under optimum pH and [SO4]. approximately half of the mineral surface is covered by su1 fate ions. Sulfate was sorbed irreversibly. Only a fraction of sorbed sulfate can be desorbed, an amount which increases with pH. Thermal analyses indicate sulfate to be strongly bonded. The presence of four infrared bands on sulfate treated surfaces indicate direct coordination of the anion to the iron cation. The above evidence, including irreversibility of sorption, supports inner sphere complexing of sulfate. Sulfate sorption on iron oxide/hydroxide minerals is thus a combination of nonspecific electrostatic attraction and mono - multi ligand exchange (including binuclear bridging) which act under different system conditions to form the basis of sulfate sorption behavior. The present observations are important in model ling of environmental systems, such as in the Direct Delayed Response Program Model, due to the significance of irreversibility of sulfate sorption on model assumptions. / Thesis / Doctor of Philosophy (PhD)

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The electron transfer mechanisms of multiheme cytochromes were examined with scanning tunneling microscopy (STM). To simulate bacterial metal reduction mediated by proteins in direct contact with mineral surfaces, monolayers of purified decaheme cytochromes from the metal-reducing bacterium Shewanella oneidensis were prepared on Au(111) surfaces. Recombinant tetracysteine sequences were added to two outermembrane decaheme cytochromes (OmcA and MtrC) from S. oneidensis MR-1 to ensure chemical immobilization on Au(111). STM images of the cytochrome monolayers showed good coverage and their shapes/sizes matched that predicted by their respective molecular masses. Current-voltage (I-V) tunneling spectroscopy revealed that OmcA and MtrC exhibit characteristic tunneling spectra. Theoretical modeling of the single-molecule tunneling spectra revealed a distinct tunneling mechanism for each cytochrome: OmcA mediates tunneling current coherently whereas MtrC temporarily traps electrons via orbital-mediated tunneling. These mechanisms suggest a superexchange electron transfer mechanism for OmcA and a redox-specific (i.e. heme-mediated) electron transfer mechanism for MtrC at mineral surfaces during bacterial metal reduction. Additionally, a novel electrochemical STM configuration was designed to measure tunneling current from multiheme cytochromes to hematite (001) surfaces in various electrolyte solutions. Current-distance (I-s) profiles on hematite (001) reveal predictable electric double layer structure that changes with ionic strength. The addition of the small tetraheme cytochrome c (STC) from S. oneidensis on insulated Au tips resulted in modified tunneling profiles that suggest STC significantly modulates the double layer. This observation is relevant to understanding metal reduction in cases where terminal metal-reducing enzymes are unable to come in direct contact with reducible mineral surfaces. Electronic coupling to the mineral surface might therefore be mediated by a localized ion swarm specific to the mineral surface. / Ph. D.

Recent studies have demonstrated that nanoscale crystalline iron oxide minerals are common in natural systems. The discipline of nanoscience suggests that these particles in the size range of approximately 1-50 nm will have properties that deviate from the bulk properties of the same material and that these properties will change as a function of particle size. This study begins to fill the void of corresponding experimental investigations that apply the principles of nanoscience to the geochemical reactivity of nanominerals. The rate of Mn²⁺(aq) oxidation on hematite with average diameters of 7.3 nm and 37 nm was measured in the presence of O₂(aq). In the pH range of 7-8, the surface area normalized rate was one to two orders of magnitude greater on the 7.3 nm average diameter particles. Based on the application of electron transfer theory, it is hypothesized that the particles with diameters less than approximately 10 nm have surface crystal chemical environments which distort the symmetry of the MnMn²⁺ surface complex, reducing the energy required to reorganize the coordinated ligands after oxidation to Mn³⁺. Cu²⁺, an analog for Mn³⁺, was used to probe for the presence and nature of the proposed changes in surface structure. Cu²⁺ and Mn³⁺ show similar electronic structure changes in response to the surrounding crystal field due to their d-electron configurations and Jahn-Teller coordinative distortions. Batch sorption experiments on hematite nanoparticles revealed a shift in the pH-dependent adsorption of Cu²⁺(aq). Specifically, an affinity sequence of 7 nm > 25 nm = 88 nm was determined based on the shift of the 7 nm sorption edge to approximately 0.8 pH units lower than that for the 25 nm and 88 nm samples. These data support the hypothesis that unique binding sites exist on the 7 nm nanoparticles that are not significantly present on the larger particles. The National Nanotechnology Initiative stresses the need to address the broader societal impacts of nanoscale research. This dissertation embraces this viewpoint through the development and inclusion of "Nano2Earth: Introducing Nanotechnology Through Investigations of Groundwater," a curriculum which combines nanoscience with the Earth sciences for high school students. / Ph. D.