Berlin 2018 – wissenschaftliches Programm

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O: Fachverband Oberflächenphysik

O 115: Molecular films: Photovoltaics, electronics and morphology (joint session O/CPP)

O 115.4: Vortrag

Freitag, 16. März 2018, 11:15–11:30, MA 144

Local near-field spectroscopy of squaraine J-aggregates — •Jinxin Zhan, Jens Brauer, Manuela Schiek, Petra Groß, and Christoph Lienau — Carl von Ossietzky Universität, Oldenburg, Germany

Investigating the relationship between structure and function of organic molecular systems is of great interest for understanding their optical and electronic properties, inter- and intra-molecular coupling, and further applications such as solar cells, transistors, and photovoltaic devices. Optical microscopy on a nanometer length scale is one promising approach to obtain such insights. Here we employ scattering-type near-field scanning optical microscopy (NSOM) to probe the local spectrum of squaraine J-aggregates (R-ProSQ-C16). We model two resonances in the far-field spectrum of the molecules as transitions from the ground state to two excited states which originate from the energy level splitting caused by the coupling between two adjacent monomers. The splitting strength and hence the transition energy is determined by the tilt angle between the two coupled monomer dipoles. Near-field spectral measurements resolve local scattering spectra in 10-nm-radius domains. They reveal that the resonance energies measured in the individual domains vary from each other. These near-field spectral measurements, in combination with our theoretical modelling, reveal local variations in the tilt angle between the two monomer dipoles.