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Single Colloidal Quantum Dots with Polymer Shells: Optical Characterization and Functionalization

Janine Keller, Universität Konstanz, Lehrstuhl für Ultrakurzzeitphysik und Photonik

Semiconductor quantum dots (QDs) are nanoscale crystals possessing discrete electronic levels as a result of strong quantum confinement in three dimensions. Size-dependent (tunable) electronic and optical properties together with large dipole moments position QDs as ideal candidates for experiments in the domain of quantum optics. Especially colloidal QDs are derived from solution and thus can be spin- or dip-coated as well as nano-mechanically manipulated, e.g. with the tip of an atomic force microscope [1]. By these means one can couple the dots to nano-plasmonic structures, e.g. nano-antennas [2].

In our recent work, we explore colloidal QDs for quantum optics applications. To improve stability, we coat single CdSe/CdS core/shell QDs with a polymer shell using miniemulsion polymerization. The resulting QD/PMMA hybrid particles (HQDs) show bright single photon emission and extremely high photostability [3]. At cryogenic temperatures, we observe lifetimes as short as 2 ns and line widths as narrow as 0.1 nm. In my talk, I will present a model  for charge and potential well configurations in QDs depending on temperature and surrounding conditions.
Using polyfluorene-chains as ligands for the QD-synthesis is a possible way to gain singly charged QDs. To this end, we validated the efficient binding of polyfluorene-chains to the QD-core. With microphotoluminescence spectroscopy, we proved a significant energy transfer from the polyfluorene to the QD eliminating any background emission from the polymer [4].
Furthermore, I will give an outlook on functionalization methods for selforganized arrangements of quantum dots in nano-plasmonic structures, such as nano-apertures in thin metal films.

[1] J. Merlein, M. Kahl, A. Zuschlag, A. Sell, A. Halm, J. Boneberg, P. Leiderer, A. Leitenstorfer, and R. Bratschitsch, Nature Photon. 2, 230 (2008).
[2] T. Hanke, J. Cesar, V. Knittel, A. Trügler, U. Hohenester, A. Leitenstorfer, and R. Bratschitsch, Nano Lett. 12, 4458 (2011).
[3] C. Negele, J. Haase, A. Budweg, A. Leitenstorfer und S. Mecking, Macromol. Rapid Commun. 34, 1145–1150 (2013).
[4] T. de Roo, J. Haase, J. Keller, C. Hinz, M. Schmid, D. V. Seletskiy, H. Cölfen, A. Leitenstorfer und S. Mecking, in preparation.

Friday, December 13, 2013, 11 a.m.

Lecture room 435, Günther-Scharowsky-Str. 1