Role of polarons, interfaces, and phonons in photocatalytic junctions

Abstract

Femtosecond to picosecond processes are often considered to be a thermalizing bath that has little effect on longer time scale photocatalytic reactions. In this talk, we will discuss when strong electron-phonon interactions can be the rate limiting step in photocatalytic materials and junctions. Specifically, high harmonic generation is used to create X-ray pulses with attosecond pulse widths and energies covering 10-150 eV. The energy range allows for multiple elemental X-ray edges to be measured simultaneously. The XUV pulse is combined with a 3-5 fs excitation pulse and a delay line to allow for transient absorption measurements. The response of the elemental X-ray edges to visible light photoexcitation is sepd. into electronic and thermal structural components using the Bethe-Salpeter equation with d. functional theory. This allows for the heat and charge transfer to be measured as a function of an element. For example, the conversion of photoexcited electrons to polarons is measured in Fe₂O₃. The time-resolved energy of electrons and holes, as well as their correlation with the acoustic and optical phonon bath, is measured in Si and Ge. Finally, the charge and heat transport is measured between each component of a metal-insulator-semiconductor junction (Ni-TiO₂-Si) using the Ni, Ti, and Si X-ray edges.