This research investigated the mechanism, kinetics and feasibility of nitrate, arsenate, and trichloroethylene inactivation on zerovalent iron (ZVI), mixed-valent iron oxides, and boron doped diamond film electrode surfaces, respectively. Nitrate ( ) is a common co-contaminant at sites remediated using permeable reactive barriers (PRBs). Therefore, understanding nitrate reactions with ZVI is important for understanding the performance of PRBs. This study investigated the reaction mechanisms of with ZVI under conditions relevant to groundwater treatment. Tafel analysis and electrochemical impedance spectroscopy were used to probe the surface reactions. Batch experiments were used to study the reaction rate of with freely corroding and cathodically protected iron wires. The removal kinetics for the air formed oxide (AFO) were 2.5 times slower than that of water formed oxide (WFO).This research also investigated the use of slowly corroding magnetite (Fe3O4) and wustite (FeO) as reactive adsorbent media for removing As(V) from potable water. Observed corrosion rates for mixed valent iron oxides were found to be 15 times slower than that of zerovalent iron under similar conditions. Electrochemical and batch and column experiments were performed to study the corrosion behavior and gain a deeper understanding on the effects of water chemistry and operating parameters, such as, empty bed contact times, influent arsenic concentrations, dissolved oxygen levels and solution pH values and other competing ions. Reaction products were analyzed by X-Ray diffraction and XPS to determine the fate of the arsenic.This research also investigated use of boron doped diamond film electrodes for reductive dechlorination of trichloroethylene (TCE). TCE reduction resulted in nearly stoichiometric production of acetate. Rates of TCE reduction were found to be independent of the electrode potential at potentials below -1 V with respect to the standard hydrogen electrode (SHE). However, at smaller overpotentials, rates of TCE reduction were dependent on the electrode potential. Short lived species analysis and density functional simulations indicate that TCE reduction may occur by formation of a surface complex between TCE and carbonyl groups present on the surface.

Since many years, the importance of thin layers increases for lots of technical uses. Beginning in the field of microelectronics, the use of thin layers spread increasingly to other areas. Coatings for surface refining and optimisation of the mechanical properties for material engineering, customisation of the surface chemistry in catalysts, as well influencing of the transmission and reflection characteristics of surfaces in optics are only some examples of the high scientific and economic weight of the thin layer technology. Thin magnetic layers are the basis of many known storage media ranging from the tape recorder to the hard disk up to the credit card. Nowadays, these thin layers again gain interest in the research field of nanoelectronics as ultrathin layers. So-called spinvalve-read/write heads being already installed in actual hard disks use the Tunnel Magneto Resistance effect for a significant rise in memory density synonymous capacity. Such read/writeheads consist of a magnetic layersystem. This use of the magnetic as well as the electric characteristics of the electrons is called spintronics. The iron oxide magnetite exhibits a high iron portion, is strong antiferrimagnetic and has a high Curie-temperature. Since many years, it is used as a magnetic pigment on already mentioned magnetic tapes. Literature [1, 2, 3, 4] considers ultrathin epitaxial layers of magnetite on magnesium oxide for uses in the spintronics as a most promising candidate, because it inheres a complete spin polarisation at Fermi-level. Moreover, thin magnetite layers serve in the chemical industry as a catalyst in the Haber- Bosch-procedure and to the dehydration of ethylbenzene to styrene. Being already used and considered to be of ongoing interest, ultrathin magnetite layers offer a wide range of technological applications in many modern industrial and scientific fields. Because there is, nevertheless, a variety of other iron oxide (cf. chapter 4), it is a matter to determine the special growth conditions of magnetite. These ultrathin iron oxide layers were grown reactively on the (001)-surfaces of the magnesium oxide substrate by molecular beam epitaxy. Besides, the surface is examined by the diffraction of low-energy electrons concerning its crystalline structure. X-ray photo electron spectroscopy approaching the stochiometry completes these first characterisations. Other investigations are carried out at HASYLAB / DESY in Hamburg by X-ray reflectivity and X-ray diffraction. The exact thickness of the layers, its crystal properties in bulk, as well as the thickness of the crystalline portion of the layers can be determined among other features of the system. The evaluation of XRR-and XRD-investigations is done via simulations with in chapter 5 introduced software packages. The reader finds the theoretical backgrounds to the used techniques in chapter 3. The experimental setups in Osnabr¨uck and Hamburg as well as the backgrounds to the preparation are presented in chapter 5. Because the formation of the different iron oxides is described in literature [5, 6, 7, 8] as mostly depending on annealing temperatures, the experimental results in chapter 6 are graded accordingly. The dependence on temperature, layer thickness and annealing time should be examined for the iron oxides possible on this substrate. The aim of this work is the preparation of ultrathin epitaxial iron oxide layers with thicknesses up to few nanometers. The main goal is to find the growth parameters for ultrathin crystalline magnetite layers.