Robust excitons inhabit soft supramolecular nanotubes.

Nature's highly efficient light-harvesting antennae, such as those found in green sulfur bacteria, consist of supramolecular building blocks that self-assemble into a hierarchy of close-packed structures. In an effort to mimic the fundamental processes that govern nature's efficient systems, it is important to elucidate the role of each level of hierarchy: from molecule, to supramolecular building block, to close-packed building blocks. Here, we study the impact of hierarchical structure. We present a model system that mirrors nature's complexity: cylinders self-assembled from cyanine-dye molecules. Our work reveals that even though close-packing may alter the cylinders' soft mesoscopic structure, robust delocalized excitons are retained: Internal order and strong excitation-transfer interactions--prerequisites for efficient energy transport--are both maintained. Our results suggest that the cylindrical geometry strongly favors robust excitons; it presents a rational design that is potentially key to nature's high efficiency, allowing construction of efficient light-harvesting devices even from soft, supramolecular materials.

Confined states of individual type-II GaSb/GaAs quantum rings studied by cross-sectional scanning tunneling spectroscopy.

Combined cross-sectional scanning tunneling microscopy and spectroscopy results reveal the interplay between the atomic structure of ring-shaped GaSb quantum dots in GaAs and the corresponding electronic properties. Hole confinement energies between 0.2 and 0.3 eV and a type-II conduction band offset of 0.1 eV are directly obtained from the data. Additionally, the hole occupancy of quantum dot states and spatially separated Coulomb-bound electron states are observed in the tunneling spectra.

Improvements of the aerosol algorithm in ozone lidar data processing by use of evolutionary strategies.

The differential absorption lidar (DIAL) at the Institut für Meteorologie und Klimaforschung has been upgraded for precise ozone and aerosol studies in the entire troposphere and the lower stratosphere. Its excellent technical performance offers the opportunity to apply improved data processing. The existing inversion algorithm is extended to derive the optical coefficients from the backscatter profiles for three wavelengths. Correlating the correction terms of the DIAL equation and the ozone concentration yields the wavelength dependence of the backscatter and extinction coefficients of the aerosol. Under some conditions, in particular if homogeneous layers are present, the backscatter-to-extinction ratio and the reference value can also be retrieved. We find the solutions by applying evolutionary strategies. From the optical coefficients obtained in this way the ozone concentration can be calculated with substantially reduced error.