Berlin 2012 – wissenschaftliches Programm

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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 8: Poster: Nanoparticles and Composite Materials

CPP 8.12: Poster

Montag, 26. März 2012, 17:30–20:00, Poster A

Photothermal spectroscopy studies of quantum dots in liquid crystals — •André Heber, Martin Pumpa, Markus Selmke, Marco Braun, Nicole Amecke, and Frank Cichos — Molecular Nanophotonics, University of Leipzig, Leipzig, Germany

Fluorophores have played an important role for single-molecule techniques but they suffer from bleaching which limits the observation time. Metallic nanoparticles can overcome this limitation. They constantly absorb light that is dissipated into the environment as heat. This temperature increase results in a change of the refractive index around the particle being detected by a probing laser beam. Usually gold nanoparticles are used as they have a large absorption cross section as compared to the 100-fold smaller one of quantum dots. We try to compensate this by observing quantum dots in a liquid crystal (5CB) slightly below the phase transition temperature from the nematic to the isotropic phase. A small heating of the quantum dot will cause the phase transition which results in a jump of the refractive index. Using this technique we are able to increase the photothermal signal by at least a factor of ten. We analyse the photothermal signal in liquid crystals and perform absorption spectroscopy on quantum dots as well as numerical calculations.