Composition-dependent electronic energy relaxation dynamics of metal domains as revealed by bimetallic AuAg(SCH) monolayer-protected clusters.

We examined the electronic relaxation dynamics for mono and bimetallic AuAg(SCH) monolayer-protected clusters (MPCs) using femtosecond time-resolved transient extinction spectroscopy. MPCs provide compositionally well-defined model systems for structure-specific determination of nanoscale electronic properties. Based on pulse-energy-dependent transient extinction data, we quantified electron-phonon coupling constants for three distinct AuAg(SCH) MPC samples, where x = 0, 0 < x < 30, and x ∼ 30, as G = (1.61 ± 0.1) × 10 W m K, G = (1.74 ± 0.1) × 10 W m K and G = (2.07 ± 0.15) × 10 W m K, respectively. These results reflect a trend of greater electron-phonon coupling efficiency with increasing silver content. Based on these data, we conclude that gold-atom replacement by silver occurs at surface sites of the 114-atom metal core of the MPC. Definitive determinations of functional response to nanoscale "alloy" formation and dopant inclusion are critical to establishing predictive models for the development of materials that feature nanoparticles as active components.