Hannover 2013 – scientific programme
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MO: Fachverband Molekülphysik
MO 23: Femtosecond Spectroscopy VI
MO 23.4: Talk
Thursday, March 21, 2013, 15:00–15:15, F 102
Femtosecond Time-Resolved Characterization of Single PTCDA Nanocrystals — •Tahir Zeb Khan, Khadga J. Karki, Mahesh Namboodiri, and Arnulf Materny — Research Center for Functional Materials and Nanomolecular Science, Jacobs University, Campus Ring 1, D-28759 Bremen, Germany
The organic semiconductor 3,4,9,10 perylene tetra carboxylic dianhydride (PTCDA) is an important model system, which helps to gain information about the processes playing a role in organic electronic devices. We have investigated thin films formed by PTCDA nanocrystals. Comparing results obtained from transient absorption experiments with different spatial resolution from few micrometers down to sub-100-nanometer resolution, different lifetimes of the photoinduced exciton states could be observed. The high spatial resolution was obtained by using a system combining femtosecond time-resolved spectroscopy with a scanning near-field optical microscope (SNOM). A series of experiments has been performed, which yielded information about the dependence of the exciton dynamics on crystallite size, layer thickness, and exciton density. We demonstrate that the SNOM approach does not only help to avoid structural inhomogeneities, but also yields results with much more well-defined excitation intensity. The latter plays an important role in nonlinear effects and specifically strongly influences the exciton annihilation dynamics in the S1 state of PTCDA. A short review of the results will be presented.