Ultrafast charge transfer in surface-enhanced Raman scattering (SERS) processes using transient reflecting grating (TRG) spectroscopy

Ultrafast dynamics was investigated for photo-excited electrons between a SERS-active gold substrate and several kinds of adsorbed dyes by using TRG spectroscopy. A charge transfer (CT) within 200 fs between them was observed for a SERS-active sample and the number of CT electrons had a strong correlation to both the relative adsorption energy states (AESs) of dyes and the enhancement factors of their SERS band. To increase the number of CT electrons, the AESs should be closer to the excited energy state of gold. A larger number of CT electrons are considered to make the enhancement of SERS band larger.