Ultrafast Charge Transfer Dynamics at Interfaces is a critical process in surface catalysis, novel electronic applications and solar energy conversion. The fast kinetics (below 100 fs) and the inhomogeneous environment complicate identifying the parameters that dominate the reaction. We are investigating the influence of structural dynamics throughout the progression of heterogeneous electron transfer by monitoring coherent oscillations in the dynamic of the excited state and the molecular cation by pump-degenerate four-wave mixing spectroscopy of the photoexcited chromophore. I will present ultrafast spectroscopic studies of model systems with well-defined variations in excess energy and dipole moment and address the importance of electronic-vibrational coupling for electron transfer.
Spatial-resolved Ultrafast Luminescence Dynamics of Single Nanowires. Transparent semiconducting nanowires are an important subject of recent experimental and theoretical investigations because of their potential applications in electronics, opto-electronics, and renewable energy. Charge carrier diffusion and lifetime are the most important parameters for any electronic application. I will show how charge carrier mobility can be extracted from contactless measurements on single ZnO nanowires with a novel femtosecond wide-field Kerr-gated UV luminescence microscope. Our work on single particle characterization is complemented by our synthesis of hierarchical tree-like nanostructure with CdSSe or CuO branches grown onto ZnO nanowire stems that are vertically-aligned on a substrate.