Tuning Chemical Interface Damping in Single Au–Ag Heterostructured Nanodumbbells by Adjusting the Au–Ag Atomic Ratio and the d-Band Center Position

Plasmon damping in Au-Ag bimetallic nanoparticles is poorly understood. Herein, we synthesized dumbbell-shaped Au-Ag nanoparticles (Au-AgDBs) with increasing Ag content (from Au-AgDB₁ to Au-AgDB₂). Au-AgDB₁ exhibited stronger damping, attributed to an interplay of the d-band center downshift, increased surface roughness, and electron transfer from Ag to Au. We further investigated chemical interface damping (CID) during the chemisorption of pyridine and 4-aminopyridine (4-AP), the latter containing an electron-donating group, on Au-AgDBs using real-time dark-field spectroscopy. Each adsorbate adopted a distinct orientation on the nanoparticle surface, governed by the nanoparticle's d-band center, which significantly affected CID. Pyridine, with overlapping molecular orbitals, enhanced CID via parallel adsorption, whereas 4-AP tended to tilt or stand upright due to steric hindrance and the resonance-active -NH₂ group, as confirmed by Raman spectroscopy. This study provides new insights into how atomic composition, nanoparticle morphology, and adsorbate orientation collectively influence CID, enabling tunable plasmon damping in Au-Ag bimetallic nanoparticles.