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Photothermal studies of single molecules and gold nanoparticles: vapor nanobubbles and conjugated polymers

Promotor: M.A.G.J. Orrit

Hou, L.
14 June 2016
Thesis in Leiden Repository

Gas bubbles in liquids are important in biomedical applications such as ultrasound imaging, drug release, or photothermal therapy. We create vapor nanobubbles in liquids around laser-heated gold nanoparticles and investigate their time-dependent properties using optical techniques. Vapor nanobubbles can show explosive behavior on the (sub-)nanosecond (10^-9s) time scale, even under continuous heating. They are highly sensitivity to acoustic pressures. From our study, we conclude that vapor nanobubbles are very interesting systems for fast all-optical light modulation and for nanoscale acoustic-wave sensing. Conjugated polymers are important organic materials in organic light emitting diodes, thin-film transistors, solar cells, or as chemical sensors. We use photothermal microscopy to study the optical absorption of single conjugated polymer molecules (MEH-PPV). Immersing the molecules in supercritical xenon as the photothermal transducing medium, we detect single conjugated polymer molecules via their absorption, and correlate this signal with photoluminescence. We measure the number of monomers in individual polymer chains and the apparent quantum yield of single conjugated molecules. The information provided by our technique will generate a better understanding of trapping and non-radiative deactivation channels of optically-induced excitations in conjugated polymers and thus facilitate the design and optimization of devices based on this important class of materials.

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