CONTENTS 1. Introduction 9662 2. Light−Matter-Related Applications Including TiO 2 9665 2.1. TiO 2 as a Photocatalyst 9665 2.2. TiO 2 in Photovoltaics 9666 3. Correlation between Phase, Surface, and Photoelectric Properties 9666 4. Optical and Electronic Properties of TiO 2 9669 4.1. Survey through Recent and Past Theoretical Work on the Band Theory of TiO 2 9669 4.2. Evolution of the Electronic Structure upon Introduction of Impurity Elements into the Host Oxide Lattice 9670 4.3. Scalability of the Electronic Properties of Intrinsic and Doped TiO 2 9675 4.4. Hybrid-Structure TiO 2 for Enhanced Photoelectric Activity 9676 5. Overview of Recent Progress in the Tailoring of the Optical Properties of TiO 2 9677 5.1. Introduction of Impurity Elements into the Host TiO 2 Lattice 9677 5.1.1. Metal Doping 9677 5.1.2. Nonmetal Doping 9680 5.1.3. Codoping 9682 5.2. Heterostructure TiO 2 9683 5.3. Dye Sensitization for Enhanced Surface Characteristics 9686 5.4. Correlation between the Orientation of Crystal Facets and Optical Properties 9688 6. X-ray Spectroscopy on the Band Structure of TiO 2 9689 6.1. Soft X-ray Spectroscopy Enabling Characterization at the Atomistic Level 9689 6.2. General Spectroscopic Features of TiO 2 9691 6.3. Multilayer Architecture and Interfacial Electronic Structure 9693 7. Conclusions and Outlook 9695 Author Information 9696 Corresponding Author 9696 Notes 9696 Biographies 9696 Acknowledgments 9697 References 9697

The X-ray absorption spectra (XAS) of lithium polysulfides (Li2Sx) of various chain lengths (x) dissolved in a model solvent are obtained from first-principles calculations. The spectra exhibit two main absorption features near the sulfur K-edge, which are unambiguously interpreted as a pre-edge near 2471 eV due to the terminal sulfur atoms at either end of the linear polysulfide dianions and a main-edge near 2473 eV due to the (x - 2) internal atoms in the chain, except in the case of Li2S2, which only has a low-energy feature. We find an almost linear dependence between the ratio of the peaks and chain length, although the linear dependence is modified by the delocalized, molecular nature of the core-excited states that can span up to six neighboring sulfur atoms. Thus, our results indicate that the ratio of the peak area, and not the peak intensities, should be used when attempting to differentiate the polysulfides from XAS.

Zinc tin oxide (Zn(1-x)Sn(x)O(y)) has been proposed as an alternative buffer layer material to the toxic, and light narrow-bandgap CdS layer in CuIn(1-x),Ga(x)Se(2) thin film solar cell modules. In this present study, synchrotron-based soft X-ray absorption and emission spectroscopies have been employed to probe the densities of states of intrinsic ZnO, Zn(1-x)Sn(x)O(y) and SnO(x) thin films grown by atomic layer deposition. A distinct variation in the bandgap is observed with increasing Sn concentration, which has been confirmed independently by combined ellipsometry-reflectometry measurements. These data correlate directly to the open circuit potentials of corresponding solar cells, indicating that the buffer layer composition is associated with a modification of the band discontinuity at the CIGS interface. Resonantly excited emission spectra, which express the admixture of unoccupied O 2p with Zn 3d, 4s, and 4p states, reveal a strong suppression in the hybridization between the O 2p conduction band and the Zn 3d valence band with increasing Sn concentration.

The electronic structure of a material plays an important role in its functionality for different applications which can be probed using synchrotron-based spectroscopy techniques. Here, various cobalt-based compounds, differing in crystal structure, ligands surrounding the central metal ion and morphology, have been studied by soft X-ray absorption spectroscopy (XAS) at the Co L-edge in order to measure the effect of these parameters on the electronic structure. A careful qualitative analysis of the spectral branching ratio and relative intensities of the L3 and L2 peaks provide useful insight into the electronic properties of compounds such as CoO/Co(OH)2, CoCl2.6H2O/CoF2.4H2O, CoCl2/CoF2, Co3O4 (bulk/nano/micro). For further detailed analysis of the XAS spectra, quantitative analysis has been performed by fitting the spectral profile with simulated spectra for a number of cobalt compounds using crystal field atomic multiplet calculations.

We report a systematic study of the film thickness dependence (0.1–1 μm) of room-temperature ferromagnetism in pure magnetron-sputtered ZnO thin films wherein a sequential transition from ferromagnetism to paramagnetism and diamagnetism as a function of film thickness is observed. The highest saturation magnetization (MS) value observed is 0.62 emu/g (0.018 μB/unit cell) for a ∼480 nm film. On doping the ZnO film with 1 at. % Mn enhances the MS value by 26%. The ferromagnetic order in ZnO matrix is believed to be defect induced. In addition, on doping with Mn hybridization between the 2p states of O and the 3d states of Mn occurs.