Spectroscopic studies of IrO2 and Bi2Ir2O7

The oxides of iridium, a 5d transition metal, have recently attracted interest in a number of scientific disciplines, ranging from fundamental solid state physics, to more applied areas of research such as spintronics and catalysis. The metallic oxides IrO2 and Bi2Ir2O7, in particular, are known to be good catalysts of the commercially important oxygen evolution reaction; IrO2 has also been identified as a promising material for spin current detection, and Bi2Ir2O7 has received attention due to its unusual magnetic response at low temperatures. In the work reported in this thesis, X-ray photoelectron spectroscopy using an Al Kα photon source (XPS), synchrotron-based hard X-ray photoelectron spectroscopy (HAXPES), X-ray emission spectroscopy (XES), X-ray absorption spectroscopy (XAS), and resonant inelastic X-ray scattering (RIXS) were used to characterize the electronic structures of IrO2 and Bi2Ir2O7. The results were compared to simulated spectra derived from the results of density functional theory calculations performed by collaborators, and analyzed in terms of qualitative models of the electronic structure. Excellent agreement between theory and experiment was observed, especially if the effects of final state lifetime broadening were accounted for. A new formalism was derived that allows final state lifetime effects to be included in band structure based RIXS simulations. The results of the theoretical calculations were also used to analyze the properties of the low energy electronic states in IrO2 and Bi2Ir2O7, and it was found that in both cases there are strong deviations from the predictions of the popular jeff = 1/2 model. The results of preliminary high pressure photoemission measurements of IrO2 are also presented in this thesis, alongside a more detailed discussion of fundamental aspects of this relatively new technique. In particular, the issue of the pressure profile that is formed around the sample and the first aperture in differentially pumped spectrometers is addressed using a combination of experimental measurements and computational fluid dynamics simulations. For the flow of N2 through a 0.3 mm aperture, the calculated pressures at the plane of the sample are tabulated for a range of sample-to-cone distances and pressures of 5.0 mbar, 9.4 mbar and 30 mbar.Open Acces

Frontier orbitals and quasiparticle energy levels in ionic liquids

Ionic liquids play an important role in many technological applications and a detailed understanding of their frontier molecular orbitals is required to optimize interfacial barriers, reactivity and stability with respect to electron injection and removal. In this work, we calculate quasiparticle energy levels of ionic liquids using first-principles many-body perturbation theory within the GW approximation and compare our results to various mean-field approaches, including semilocal and hybrid density-functional theory and Hartree–Fock. We find that the mean-field results depend qualitatively and quantitatively on the treatment of exchange–correlation effects, while GW calculations produce results that are in excellent agreement with experimental photoelectron spectra of gas phase ion pairs and ionic liquids. These results establish the GW approach as a valuable tool for understanding the electronic structures of ionic liquids

Captured by Evil: The Idea of Corruption in Law

Corruption is one of the most powerful words in the English language. When it comes to the treatment of corruption by law, however, corruption is a troubled concept. With increasing recognition of the costs of corruption for economic development, democratic governance, international aid programs, and other world goals, attempts to articulate what this destructive force is have led to an avalanche of theoretical writing. In the last fifteen years, corruption has been variously defined as the violation of law, a public servant\u27s breach of public duty, an agent\u27s betrayal of a principal\u27s interests, the pursuit of secrecy, the denial of equality in political influence, and other ways. In the end, however, all of these efforts fall short. Corruption is more than law-breaking: it is more than breaching public duties. To say that A is a thief or that A has breached his duty is not to say that A is corrupt. The latter is far more powerful, far more emotional, far more essential than the others. It is more than secrecy, or the denial of equal opportunity. It is a searing indictment, somehow, not only of A\u27s act but of A\u27s character. It is a statement not only of what A has done, but of what A has become. Corruption is, I argue, a far more powerful idea than these existing legal understandings have articulated: it is the idea of capture by evil, the possession of the individual by evil, in law. Just as we once believed in corruption of the blood in American law, which decreed that offspring of those who had committed crimes were believed to be irrevocably tainted by their parents\u27 depravity, so we still retain - through the idea of corruption - the belief that individual evil extends beyond acts of wrongdoing, or the denial of equal opportunity, or breach of the public trust. It is this idea of corruption, I argue - the idea of capture by evil - that, although unarticulated, drives our understandings of corruption in law. It drives our understanding of corrupt judges, who, once corrupt, we believe will act so in every case. It drives our understanding of campaign finance reform, where we fear deep corruption of the process from the occurrence of corrupt acts. It drives our understanding of corruption as a systemic effect and systemic influence, which presents institutional dangers that are greater than other crimes, and that requires purgation rather than simple law enforcement. This Article explores this deeper understanding of corruption, its impacts in areas such as judicial corruption and campaign finance reform, and its implications for the principle of the rule of law

Combining Time-Dependent Density Functional Theory and the ΔSCF Approach for Accurate Core-Electron Spectra

Spectroscopies that probe electronic excitations from core levels into unoccupied orbitals, such as X-ray absorption spectroscopy and electron energy loss spectroscopy, are widely used to gain insight into the electronic and chemical structure of materials. To support the interpretation of experimental spectra, we assess the performance of a first-principles approach that combines linear-response time-dependent density (TDDFT) functional theory with the Δ self-consistent field (ΔSCF) approach. In particular, we first use TDDFT to calculate the core-level spectrum and then shift the spectrum such that the lowest excitation energy from TDDFT agrees with that from ΔSCF. We apply this method to several small molecules and find encouraging agreement between calculated and measured spectra