Dresden 2017 – wissenschaftliches Programm
Bereiche | Tage | Auswahl | Suche | Aktualisierungen | Downloads | Hilfe
O: Fachverband Oberflächenphysik
O 75: Ultrafast Electron and Spin Dynamics
O 75.12: Vortrag
Mittwoch, 22. März 2017, 17:45–18:00, TRE Phy
Vibrational relaxation and migration dynamics of excitons in sexithiophene/Au(111) — Wibke Bronsch1, Sebastian Baum1, Kristof Zielke1, Malte L. Wansleben2, Martin Weinelt1, and •Cornelius Gahl1 — 1Freie Universität Berlin, Institut für Experimentalphysik, Arnimallee 14, 14195 Berlin — 2Physikalisch-Technische Bundesanstalt, Abbestr. 2-12 10587 Berlin
The primary optical excitations in organic semiconductors are excitons. The corresponding absorption bands are commonly strongly broadened due to coupling to vibrational excitations, as known from optical spectroscopy. In organic electronics, the dynamics of such excitonic states concerning their energetic evolution as well as their migration through the material are decisive for the performance of a device. We investigated the exciton dynamics by time-resolved two-photon photoemission (2PPE) spectroscopy in the model system of sexithiophene (6T) on the Au(111) surface. In crystalline 6T films, vibrational excess energy is dissipated on a time scale of <100 fs resulting in an excitonic state which is stable in energy for >100 ps. In amorphous 6T films, however, the energetic relaxation from a broad initial distribution of excited states is strongly slowed down and reaches an excitonic state with a binding energy comparable to that in the crystalline film on a time scale >10 ps. This slow process is attributed to migration of excitons towards sites with higher binding energy. Thus the morphology of the organic layer strongly influences the excited state dynamics and energetics relevant for organic electronics.