Photoproduction of jets and heavy flavors at future polarized ep-colliders

We study photoproduction of jets and heavy flavors in a polarized collider mode of HERA and in polarized ep collisions at √S ≈ GeV. We examine the sensitivity of the cross sections and their asymmetries to the proton’s polarized gluon distribution and to the completely unknown parton distributions of longitudinally polarized photons.     

Control of Intrachain Morphology in the Formation of Polyfluorene Aggregates on the Single-Molecule Level

Controlling the morphology of π-conjugated polymers for organic optoelectronic devices has long been a goal in the field of materials science. Since the morphology of a polymer chain is closely intertwined with its photophysical properties, it is desirable to be able to change the arrangement of the polymers at will. We investigate the π-conjugated polymer poly(9,9-dioctylfluorene) (PFO), which can exist in three distinctly different structural phases: the α-, β-, and γ-phase. Every phase has a different chain structure and a unique photoluminescence (PL) spectrum. Due to its unique properties and the pronounced spectral structure-property relations, PFO can be used as a model system to study the morphology of π-conjugated polymers. To avoid ensemble averaging, we examine the PL spectrum of single PFO chains embedded in a non-fluorescent matrix. With single-molecule spectroscopy the structural phase of every single chain can be determined, and changes can be monitored very easily. To manipulate the morphology, solvent vapor annealing (SVA) was applied, which leads to a diffusion of the polymer chains in the matrix. The β- and γ-phases appear during the self-assembly of single α-phase PFO chains into mesoscopic aggregates. The extent of β- and γ-phase formation is directed by the solvent-swelling protocol used for aggregation. Aggregation unequivocally promotes formation of the more planar β- and γ-phases. Once these lower-energy more ordered structural phases are formed, SVA cannot return the polymer chain to the less ordered phase by aggregate swelling.     

Eine Verallgemeinerung der konfokalen Flächen zweiter Ordnung

Ohne Zusammenfassung     

Differentiation between Shallow and Deep Charge Trap States on Single Poly(3‐hexylthiophene) Chains through Fluorescence Photon Statistics

Blinking of the photoluminescence (PL) emitted from individual conjugated polymer chains is one of the central observations made by single‐molecule spectroscopy (SMS). Important information, for example regarding excitation energy transfer, can be extracted by evaluating dynamic quenching. However, the nature of trap states, which are responsible for PL quenching, often remains obscured. We present a detailed investigation of the photon statistics of single poly(3‐hexylthiophene) (P3HT) chains obtained by SMS. The photon statistics provide a measure of the number and brightness of independently emitting areas on a single chain. These observables can be followed during blinking. A decrease in PL intensity is shown to be correlated with either 1) a decrease in the average brightness of the emitting sites; or 2) a decrease in the number of emitting regions. We attribute these phenomena to the formation of 1) shallow charge traps, which can weakly affect all emitting areas of a single chain at once; and 2) deep traps, which have a strong effect on small regions within the single chains.     

Current conservation and the parton structure of the longitudinally polarized photon

The implications of current conservation for radiatively generated parton distributions of longitudinally polarized photons are studied in detail. A particular, physically motivated, set of polarized parton distributions is presented explicitly.