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

TL;DR

This study demonstrates that steady-state photomodulated X-ray absorption spectroscopy can estimate electron and hole distributions in plasmonic photocatalysts, providing a new approach beyond ultrafast pulsed laser methods.

Contribution

It introduces a method to determine quasi-equilibrium carrier distributions using steady-state X-ray spectra and ab initio modeling, expanding analysis capabilities for photocatalytic materials.

Findings

Carrier distributions can be estimated from steady-state spectra.

The method is robust even with noisy data.

Ab initio models effectively interpret experimental spectra.

Abstract

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.