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MO: Fachverband Molekülphysik

MO 9: Femtosecond Spectroscopy II

MO 9.7: Vortrag

Dienstag, 13. März 2012, 12:15–12:30, V38.03

Femtosecond Pump-Probe Scanning Near-Field Optical Microscopy (PP-SNOM): Sub-Wavelength Resolution Chemical Imaging and Local Dynamics — •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

Femtosecond time-resolved pump-probe (PP) spectroscopy techniques allow for the investigation of ultrafast dynamics of molecules. Scanning near-field optical microscopy (SNOM) is capable of generating images with spatial resolution below diffraction limit. In our work, we have combined these two techniques enabling us to record nanoscale images non-invasively along with chemical specificity and local probing of the molecular dynamics. We present results of PP-SNOM investigations of thin films of the organic semiconductor 3,4,9,10 perylene tetra carboxylic dianhydride (PTCDA). The exciton dynamics of a 160 nm thick PTCDA layer composed of nano-crystals on glass was locally probed with a SNOM tip allowing for 100 nm spatial resolution. Intensity-dependent exciton dynamics observed at exciton densities higher than 10¹⁹ cm⁻³ is attributed to exciton-exciton annihilation. Differences found for the annihilation constant found in far and near-field investigations are discussed.