The electronic structure of some transition metal compounds, specifically, Ca-doped LaMnO3, fundamental Mn oxides (MnO, Mn2O3, Mn3O4, and MnO2), and Fe-doped ZnO is studied using a combination of soft X-ray spectroscopy and atomic multiplet calculations. X-ray absorption spectroscopy (XAS) and X-ray emission spectroscopy (XES) are used as experimental tools to probe the unoccupied and occupied partial density of electronic states,respectively.<p> Ca-doped LaMnO3 perovskites have attracted great attention due to their colossal magnetoresistance and a wide range of magnetic and structural transitions. The magnetic and charge transport properties of these perovskites are directly related with Mn 3d-occupancy or Mn-valency and therefore, an investigation of the Mn-valence at Ca-doped LaMnO3 system is important. In this system, the Mn-valency is generally considered as a mixture of Mn3+ and Mn4+. But my research suggests the presence of Mn2+ at the surface of Ca-doped LaMnO3 samples. It is observed that increasing Ca-doping decreases Mn2+ concentration, and conversely, increases Mn3+ concentration. High temperature annealing at 1000 °C in air leads to the full reduction of surface Mn2+. Mechanisms for these observations are proposed in this study.<p> Mn oxides (MnO, Mn2O3, Mn3O4, and MnO2) are often used as reference standards for determining the Mn-valency in Mn-related complex systems and therefore a detailed understanding of their electronic structure is necessary. The Mn L2,3 XAS and O K XAS are measured for the four Mn oxides consisting of three common Mn oxidation states (Mn2+ in MnO, Mn3+ in Mn2O3, mixture of Mn2+ and Mn3+ in Mn3O4, and Mn4+ in MnO2). A significant energy shift with a systematic trend is observed in measured Mn L2,3 and O K absorption edges. These energy shifts are identified as a characteristic shift for different Mn oxidation states. Mn L2,3 Resonant Inelastic X-ray Scattering (RIXS) spectroscopy is demonstrated as a powerful tool in describing low energy excitations, e.g. d-d excitations and charge-transfer excited states in Mn oxides. For the first time, a RIXS study of Mn2O3,Mn3O4, and MnO2 is accomplished. Atomic multiplet calculations are used to successfully reproduce the energy positions and intensity variations of d-d excitation peaks observed in the experiment, and thus to describe the experimental RIXS spectra.<p> Finally, the local electronic structure of Fe implanted ZnO samples, a useful diluted magnetic semiconductor for spintronics, is investigated to shed light on the existing debate about the origin of ferromagnetism in these materials. Fe L2,3 XAS reveals that doped Fe ions are present in both Fe2+ and Fe3+ valence states. A combined theoretical and experimental study shows that doped ions are incorporated into Zn-sites of ZnO in tetrahedral symmetry. Fe L3- RIXS measurements demonstrate that a high Fe-ion dose of 8 × 107 cm-2 causes formation of FeO clusters, while low dose samples exhibit more free carriers.

The electronic structure of some transition metal compounds, specifically, Ca-doped LaMnO3, fundamental Mn oxides (MnO, Mn2O3, Mn3O4, and MnO2), and Fe-doped ZnO is studied using a combination of soft X-ray spectroscopy and atomic multiplet calculations. X-ray absorption spectroscopy (XAS) and X-ray emission spectroscopy (XES) are used as experimental tools to probe the unoccupied and occupied partial density of electronic states,respectively.<p> Ca-doped LaMnO3 perovskites have attracted great attention due to their colossal magnetoresistance and a wide range of magnetic and structural transitions. The magnetic and charge transport properties of these perovskites are directly related with Mn 3d-occupancy or Mn-valency and therefore, an investigation of the Mn-valence at Ca-doped LaMnO3 system is important. In this system, the Mn-valency is generally considered as a mixture of Mn3+ and Mn4+. But my research suggests the presence of Mn2+ at the surface of Ca-doped LaMnO3 samples. It is observed that increasing Ca-doping decreases Mn2+ concentration, and conversely, increases Mn3+ concentration. High temperature annealing at 1000 °C in air leads to the full reduction of surface Mn2+. Mechanisms for these observations are proposed in this study.<p> Mn oxides (MnO, Mn2O3, Mn3O4, and MnO2) are often used as reference standards for determining the Mn-valency in Mn-related complex systems and therefore a detailed understanding of their electronic structure is necessary. The Mn L2,3 XAS and O K XAS are measured for the four Mn oxides consisting of three common Mn oxidation states (Mn2+ in MnO, Mn3+ in Mn2O3, mixture of Mn2+ and Mn3+ in Mn3O4, and Mn4+ in MnO2). A significant energy shift with a systematic trend is observed in measured Mn L2,3 and O K absorption edges. These energy shifts are identified as a characteristic shift for different Mn oxidation states. Mn L2,3 Resonant Inelastic X-ray Scattering (RIXS) spectroscopy is demonstrated as a powerful tool in describing low energy excitations, e.g. d-d excitations and charge-transfer excited states in Mn oxides. For the first time, a RIXS study of Mn2O3,Mn3O4, and MnO2 is accomplished. Atomic multiplet calculations are used to successfully reproduce the energy positions and intensity variations of d-d excitation peaks observed in the experiment, and thus to describe the experimental RIXS spectra.<p> Finally, the local electronic structure of Fe implanted ZnO samples, a useful diluted magnetic semiconductor for spintronics, is investigated to shed light on the existing debate about the origin of ferromagnetism in these materials. Fe L2,3 XAS reveals that doped Fe ions are present in both Fe2+ and Fe3+ valence states. A combined theoretical and experimental study shows that doped ions are incorporated into Zn-sites of ZnO in tetrahedral symmetry. Fe L3- RIXS measurements demonstrate that a high Fe-ion dose of 8 × 107 cm-2 causes formation of FeO clusters, while low dose samples exhibit more free carriers.

Manganese (Mn) is an important element in soil, it occur natural in minerals and precipitated as Mn-oxides. Several factors could decide the solubility and mobility of Mn in soil water. In this study, the impact of road de-icing salts (NaCl) on manganese mobilization and transport to groundwater in roadside soils has been investigated by leaching tests. Generally, in the salt solution leachates, the water-soluble concentrations of Mn tended to increase with elevated salt concentrations, suggesting that ion exchange mainly affected the mobilization. The process was also attributed to the complexion with Cl. Associated with exchangeable concentration of Mn and soil properties such as pH and acidity, the mobilizations of Mn varied. Mn-oxides can dissolve when reduced condition exists, therefore the oxalate extractable Mn was extracted to estimate the change of redox potential condition in roadside soils. The redox potential of soil samples is higher in general. Redox condition has little effect on the Mn solubility and mobility in this research. Although groundwater samples indicated that only a few periods and sites were under threaten of elevated concentrations of manganese, there is still great risk of transport of high water-soluble concentrations of Mn in roadside soils to groundwater, especially the areas exposed to de-icing salts. In addition, lower value of Mn concentrations in groundwater for considering good drinking water quality for the well-being of children should be paid more attention to.

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