Radiation damage in biomimetic dye molecules for solar cells

Strong Opto-Structural Coupling in Low Dimensional GeSe3 Films

Chalcogenide glasses as nanoscale thin films have become leading candidates for several optical and photonic technologies, ranging from reflective displays and filters to photonic memories. Current material systems, however, show strong optical absorption which limits their performance efficiencies and complicates device level integration. Herein, we report sputter deposited thin films of GeSe₃, which are low loss and in which the flexible nature of the atomic structure results in thermally activated tunability in the refractive index as well as in the film's physical volume. Such changes, which occur beyond a threshold temperature are observed to be accumulative and directed toward a more equilibrium amorphous state of the film, instead of crystallization. Our results provide insight into a new type of configurability that is based on strong coupling in the material's opto-structural properties. The low optical losses in this material system combined with the tunability in the optical properties in the visible and near-infrared have direct application in higher performing optical coatings and in corrective optics.

A sealable ultrathin window sample cell for the study of liquids by means of soft X-ray spectroscopy

A new sample cell concept for the analysis of liquids or solid-liquid interfaces using soft X-ray spectroscopy is presented, which enables the complete sealing of the cell as well as the transport into vacuum via, for example, a load-lock system. The cell uses pressure monitoring and active as well as passive pressure regulation systems, thereby facilitating the full control over the pressure during filling, sealing, evacuation, and measurement. The cell design and sample preparation as well as the crucial sealing procedure are explained in detail. As a first proof-of-principle experiment, successful nitrogen K-edge fluorescence yield near-edge X-ray absorption fine structure experiments of a biomolecular solution are presented. For this purpose, it is shown that the careful evaluation of all involved parameters, such as window type or photon flux, is desirable for optimizing the experimental result.

Soft x-ray irradiation effects of Li₂O₂, Li₂CO₃ and Li₂O revealed by absorption spectroscopy

Li(2)O(2), Li(2)CO(3), and Li(2)O are three critical compounds in lithium-air and lithium-ion energy storage systems. Extensive measurements have been carried out to study the chemical species and their evolutions at difference stages of the device operation. While x-ray spectroscopy has been demonstrated to be one of the most powerful tools for such purpose, no systematic study on the irradiation effects have been reported. Here we carry out extensive time, position, and irradiation dependent Li K-edge soft x-ray absorption spectroscopy on these compounds with so far the best energy resolution. The ultra-high resolution in the current study allows the features in the absorption spectra to be well-resolved. The spectral lineshape thus serves as the fingerprints of these compounds, enabling the tracking of their evolution under x-ray irradiation. We found that both Li(2)O(2) and Li(2)CO(3) evidently evolve towards Li(2)O under the soft x-ray irradiation with Li(2)CO(3) exhibiting a surprisingly higher sensitivity to x-rays than Li(2)O(2). On the other hand, Li(2)O remains the most stable compound despite experiencing substantial irradiation dose. We thus conclude that high resolution soft x-ray spectroscopy could unambiguously fingerprint different chemical species, but special cautions on irradiation effects would be needed in performing the experiments and interpreting the data properly.

Renormalization of optical excitations in molecules near a metal surface

The lowest electronic excitations of benzene and a set of donor-acceptor molecular complexes are calculated for the gas phase and on the Al(111) surface using the many-body Bethe-Salpeter equation. The energy of the charge-transfer excitations obtained for the gas phase complexes are found to be around 10% lower than the experimental values. When the molecules are placed outside the surface, the enhanced screening from the metal reduces the exciton binding energies by several eVs and the transition energies by up to 1 eV depending on the size of the transition-generated dipole. As a striking consequence we find that close to the metal surface the optical gap of benzene can exceed its quasiparticle gap. A classical image charge model for the screened Coulomb interaction can account for all these effects which, on the other hand, are completely missed by standard time-dependent density functional theory.