Atom-Specific Probing of Electron Dynamics in an Atomic Adsorbate by Time-Resolved X-ray Spectroscopy

TL;DR

This study uses time-resolved X-ray spectroscopy to investigate ultrafast electron dynamics in carbon adsorbed on nickel, revealing rapid electronic changes and subsequent thermalization after laser excitation.

Contribution

It provides the first direct observation of atom-specific ultrafast electron dynamics in an adsorbate using time-resolved X-ray spectroscopy.

Findings

Ultrafast (~100 fs) changes in XAS and XES indicating hot electron-hole pair formation.

Slower ps-scale changes consistent with thermalization of the C/Ni system.

Density functional theory supports the experimental interpretation.

Abstract

The electronic excitation occurring on adsorbates at ultrafast time scales from optical lasers that initiate surface chemical reactions is still an open question. Here, we report the ultrafast temporal evolution of X-ray absorption spectroscopy (XAS) and X-ray emission spectroscopy (XES) of a simple well known adsorbate prototype system, namely carbon (C) atoms adsorbed on a nickel (Ni(100)) surface, following intense laser optical pumping at 400 nm. We observe ultrafast (~100 fs) changes in both XAS and XES showing clear signatures of the formation of a hot electron-hole pair distribution on the adsorbate. This is followed by slower changes on a few ps time scale, shown to be consistent with thermalization of the complete C/Ni system. Density functional theory spectrum simulations support this interpretation.