Elucidating Interplay of Chemical and Metal Interface Damping in Single Gold Nanorods Coated with an Ultrathin Palladium Shell

Understanding plasmon damping pathways in gold nanoparticles is crucial for its efficient utilization in photochemical processes and biosensing experiments. However, elucidating the competition and interplay between chemical and metal interface damping pathways remains a significant challenge. Herein, we investigate the plasmon decay pathways of thiolated ultrathin palladium (Pd)-coated gold nanorods (AuNRs@Pd) by using dark-field (DF) spectroscopy and surface-enhanced Raman spectroscopy (SERS). AuNRs@Pd were synthesized via bottom-up epitaxial Pd growth at five Pd precursor concentrations. The resulting AuNRs@Pd exhibited a redshift and line width broadening in the DF scattering spectra as the Pd loading on the nanoparticles increased. The attachment of thiol adsorbates (thiophenol) to the nanoparticle surface induced further redshift and narrowed the line width, which was particularly pronounced with increased Pd loading. Electron-withdrawing adsorbates (<i>p</i>-nitrothiophenol) on the nanoparticle surface led to line width narrowing and redshift, attributed to reduced electron density on the AuNR core lattices. This electron density reduction was confirmed through SERS, with AuNRs@Pd₅₃ demonstrating the highest enhancement factor at four Raman peak points. Therefore, we elucidate plausible plasmon decay pathways under the coexistence of chemical interface damping and metal interface damping in single AuNRs@Pd.