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Date: Tuesday, September 3, 2013
Time: 11:00 am
Speaker: Alex Weber-Bargioni, The Molecular Foundry
Title: Investigating the Propagation of Optically Excited States and Optoelectronic Processes in Nano Building Block Assemblies
Location: 67-3111       Chemla room

Controlling individual excited states and their deliberate movement through a material is one of the ultimate goals that will provide material scientist with a complete new freedom to develop novel material functionalities. Realizing such a control would enable to direct energy to specific sites in a material where specific work can be performed. Nano materials have in principle the potential to realize this vision since the material property determining electronic structure can be tuned via geometry, material composition, interfaces and environment. However, we are still far away from this sort of control. This requires band engineering that entails an entire new set of engineering rules for the nm world and the appropriate characterization techniques at the relevant length scales.

Our approach to work towards this vision is developing tools to map the transport of optically excited states through organic and inorganic nano building block assemblies. By using nano optics we excite locally our nano material composition and map spatially independent the energy flow by detecting either the local photo luminescence or the local photo current. The organic assemblies are small molecule OPV materials where we study exciton diffusion and means to reduce exciton binding energy. The inorganic assemblies are 1 and 2-D assembled CdSe Nano Crystal assemblies where we want to understand Foerster Resonant Energy Transport mechanisms.  Another system that has interesting potential to efficiently move energy from one point to the other are nanowire systems and how local defect states enhance photo charge recombination, reducing the transport efficiency of excited states.

In the second part I will show our work on understanding fundamental opto electronic processes on potential work sites in these assemblies. One specific system we are interested in is iron oxide as potential photo catalyst. Our aim here is to correlate local morphology, electronic structure and photo-catalytic activity to get precise insight into the photo catalytic process that could eventually be fed by the energy transporting nano building block assembly.