The electronic excitation occurring on adsorbates at ultrafast timescales 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 picoseconds timescale, shown to be consistent with thermalization of the complete C/Ni system. Density functional theory spectrum simulations support this interpretation.
S. Schreck et al., Phys. Rev. Lett. 129, 276001 (2022). https://doi.org/10.1103/PhysRevLett.129.276001
Supplemental material: Details on optical absorption in C/Ni; the two-temperature model; experimental methods; computational methods; XAS from different adsorbate geometries; and discussion of selective vibrational excitation
American Physical Society