Stuttgart 2012 – wissenschaftliches Programm

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MO: Fachverband Molekülphysik

MO 13: Poster 1: Cold Molecules, Femtosecond Spectroscopy, Molecular Dynamics

MO 13.20: Poster

Dienstag, 13. März 2012, 16:30–19:00, Poster.IV

Femtosecond Time-Resolved Transient Grating Spectroscopy for the Investigation of Exciton Dynamics in Thin Films of PTCDA — •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

Elementary processes like energy transfer, charge transport, and exciton diffusion in thin films occur on time scales of femtoseconds. Time-resolved photo-electron spectroscopy, a technique limited to specialized ultra-high vacuum environment and the proper choice of substrate, has been used to study ultrafast processes in sub-nanometer thin films so far. In our contribution, we show that a transient (population) grating created by the interference of femtosecond laser pulses can be applied successfully to access ultrafast processes in such films under ambient conditions. Our investigations of exciton dynamics in 1.4 ± 0.2 and 0.4 ± 0.2 nm thin films, formed by nano crystals of 3,4,9,10-perylenetetracarboxylic dianhydride (PTCDA) on glass and mica, show that the dynamics differ with the crystal size, possibly due to the confinement-induced changes in the electronic structure. The technique is sensitive enough to investigate the dynamics in systems, where only 20% of the surface is covered by nano crystals. This is an important prerequisite for studying ultrafast dynamics on surfaces, interfaces, functionalized materials, organic semiconductors, and quantum phenomena in ordered structures of reduced dimensions, such as quantum dots and graphene sheets.