Speaker
Description
Charge transfer processes are ubiquitous in nature. They are responsible for energy transport and signal transduction in biomolecular systems. Charge carrier dynamics play also key roles in light harvesting systems used for solar cell technologies and hydrogen fuel cells. Probing the transient local charge densities with high spatio-temporal resolution is a prerequisite for a better understanding of ultrafast redox reactions that are at play in these systems. In the past century, X-ray spectroscopy has been a method of choice to probe the local electronic structure of matter. With the advent of ultrashort soft X-ray sources based on Free Electron Lasers and High-order harmonic generation using table-top femtosecond lasers, time-resolved measurements of the elementary steps occurring in charge transfer processes has now become feasible.
In our group, we aim to investigate ultrafast charge transfer processes occurring in donor-acceptor molecular systems in solution and the carrier dynamics in metal-oxide semiconductors by time-resolved soft X-ray spectroscopy. We will present the high harmonic source that we have recently developed providing femtosecond soft X-ray pulses in the water window spectral range. The source was first used to characterize the soft X-ray absorption spectra of simple molecules and ions in aqueous solution and of Fe$_2$O$_3$ thin materials. We will present as well our first time-resolved investigation of the ionization dynamics of gas-phase molecules using the newly developed source. Our results pave the way towards the investigation of femtosecond charge flow in solutes and solids.
