SERS Monitoring Hot Electron Generation in Plasmonic Silver Nanocube Monolayers

Optimizing hot electron generation is important for increasing the efficiency of light harvesting in photovoltaics and photocatalysis. Surface-enhanced Raman spectroscopy (SERS) is a valuable tool to assess the extent of such electron production as it enables monitoring of the hot electron-driven chemical reactions. In this work, SERS was used to compare the hot electrons generated when two localized surface plasmon resonance (LSPR) modes present in plasmonic substrates prepared using silver nanocubes (AgNC) were excited: the dipole LSPR mode and the coupled LSPR mode. The silver plasmonic monolayers were prepared on polystyrene-coated glass slides at various nanoparticle densities and therefore varying intensities of the dipolar and coupled resonances. Dehalogenation of bromothiophenol and chlorothiophenol was used as a hot electron sensitive reaction. The dependence of the reaction yield on the excitation wavelength, power, and extent of plasmonic coupling was assessed by monitoring SERS spectral evolution. It was found that excitation of the dipole mode resulted in a hot electron yield higher than that of the coupling mode for the substrates used. Additionally, it was found that the hot electron yield for the AgNC substrates decreased as the coupling mode strength increased. This work shows the need for a better control over the plasmonic substrate fabrication and characterization methods to allow improved hot electron generation from the coupled modes.