RESUMEN
Soft x-ray emission and absorption spectroscopic data are reported for the O 1s region of a single crystal of UO2, a polycrystalline NpO2 sample, and a single crystal of PuO2. The experimental data are interpreted using first-principles correlated-electron calculations within the framework of the density functional theory with added Coulomb U interaction (DFT+U). A detailed analysis regarding the origin of different structures in the x-ray emission and x-ray absorption spectra is given and the effect of varying the intra-atomic Coulomb interaction-U for the 5 f electrons is investigated. Our data indicate that O 1s x-ray absorption and emission spectroscopies can, in combination with DFT+U calculations, successfully be used to study 5 f -shell Coulomb correlation effects in dioxides of light actinides. The values for the Coulomb U parameter in these dioxides are derived to be in the range of 4-5 eV.
RESUMEN
An instrumental and experimental setup for soft x-ray spectroscopy meeting the requirements of a closed source for radioactivity is described. The system consists of a vacuum sealed cell containing the sample, mounted on a tubing system to ensure compatibility with most standard manipulators. The soft x rays penetrate a thin x-ray window separating the interior of the cell from the vacuum in the experimental chamber. Our first results for single crystal PuO(2) confirm the feasibility of experiments using the setup. The results are consistent with results of first principles calculations and previously recorded spectra obtained using a standard open source setup. The results show that the closed source experimental system can be used to collect valuable experimental data from radioactive materials.
RESUMEN
Soft x-ray emission spectroscopy was used to characterize the electronic structure of seven copper nitride films, one synthesized with atomic layer deposition (ALD) and six grown with chemical vapor deposition (CVD) at different preparation temperatures. Interpretation of the x-ray emission spectra was supported by calculations of the electronic structure for bulk pure Cu(3)N and Cu(3)N with: an excess of Cu atoms, oxygen or carbon impurities, and N vacancies. The calculations are shown to describe the experimental spectra quite well. Analysis of the x-ray spectra suggests that films grown in copper rich environments and above a cut-off temperature of approximately 360 °C have a growing fraction of copper enriched areas, while films prepared below this temperature do not have these areas with excess copper.