Relaxation, transport, and recombination of photoexcited charge carriers in solids occurs within femto- to picoseconds. To investigate these ultrafast processes within nanostructures and nanostructured materials on their natural time and length scale, we combine photoemission electron microscopy (PEEM) with an optical pump-probe approach based on femtosecond laser pulses. In PEEM, high resolution images of the sample (down to 40 nm resolution) are created with photoelectrons emitted from the sample surface via UV light illumination. In Tr-PEEM, we use a femtosecond probe pulse to trigger generation of photoelectrons at a controlled time delay after the sample has been excited by a femtosecond pump pulse. We use advanced optical techniques to create visible/near-IR pump and UV probe pulses as short as 10fs, enabling us to resolve dynamical processes even within few tens of fs after optical excitation. Our ongoing research focuses on ultrafast dynamics of photoexcited charge carriers in metal and semiconductor nanostructures and their correlation with local structure and material composition.
Wittenbecher, L.; Viñas Boström, E.; Vogelsang, J.; Lehman, S.; Dick, K. A.; Verdozzi, C.; Zigmantas, D.; Mikkelsen, A. Unraveling the Ultrafast Hot Electron Dynamics in Semiconductor Nanowires. ACS Nano 2021. https://doi.org/10.1021/acsnano.0c08101.