Direct and real-time observation of hole transport dynamics in anatase TiO2 using X-ray free-electron laser

Direct and real-time observation of the excess holes in an element-specific and energylevel-specific manner is a challenging task. Here the authors present a complete hole dynamics of photo-excited anatase TiO2 with 100 femto-second resolution. Carrier dynamics affects photocatalytic systems, but direct and real-time observations in an element-specific and energy-level-specific manner are challenging. In this study, we demonstrate that the dynamics of photo-generated holes in metal oxides can be directly probed by using femtosecond X-ray absorption spectroscopy at an X-ray free-electron laser. We identify the energy level and life time of holes with a long life time (230 pico-seconds) in nano-crystal materials. We also observe that trapped holes show an energy distribution in the bandgap region with a formation time of 0.3 pico-seconds and a decay time of 8.0 pico-seconds at room temperature. We corroborate the dynamics of the electrons by using X-ray absorption spectroscopy at the metal L-edges in a consistent explanation with that of the holes.

Automated summary

In this study, the authors directly observed the dynamics of photo-generated holes in metal oxides using femtosecond X-ray absorption spectroscopy and identified the energy level and lifetime of these holes. They also observed the energy distribution, formation time, and decay time of trapped holes in the bandgap region of nano-crystal materials. The dynamics of electrons were also confirmed using X-ray absorption spectroscopy, providing a consistent explanation with that of the holes.