Determining Quasi-Equilibrium Electron and Hole Distributions from Plasmonic Photocatalysts using Photomodulated X-ray Absorption Spectroscopy

Kavli Affiliate: Scott K. Cushing

| First 5 Authors: Levi D. Palmer, Wonseok Lee, Chung Li Dong, Ru-Shi Liu, Nianqiang Wu

| Summary:

Most photocatalytic and photovoltaic devices operate under broadband,
constant illumination. Electron and hole dynamics in these devices, however,
are usually measured using ultrafast pulsed lasers in a narrow wavelength
range. In this work, we prove that steady-state, photomodulated x-ray spectra
from a non-time-resolved synchrotron beamline can be used to estimate electron
and hole distributions. A set of plasmonic metal core-shell nanoparticles is
designed to systematically isolate photothermal, hot electron, and thermalized
electron-hole pairs in a TiO2 shell. Steady-state changes in the Ti L2,3 edge
are measured with and without continuous-wave illumination of the
nanoparticle’s localized surface plasmon resonance. Ab initio excited-state
x-ray theory developed for transient x-ray measurements is then applied to
model the experimental spectra in an attempt to extract the resultant
steady-state carrier distributions. The results suggest that, within error, the
quasi-equilibrium carrier distribution can be determined even from relatively
noisy data with mixed excited-state phenomena.

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