Unified description of thermal and nonthermal hot carriers in plasmonic photocatalysis

Abstract

The damping of surface plasmons generates hot carriers, which holds promise for photoelectric conversion and photocatalysis. Recent studies have revealed the nonequilibrium characters of the plasmonic hot carriers and their nonadiabatic coupling to molecular vibrations. Yet, the precise mechanism of plasmonic photocatalysis remains elusive and controversial. Here, we present a unified description of thermal and nonthermal hot carriers in the dynamics of vibrational excitation and photodissocation, where a quantitative comparison between the two mechanisms can be made. We revisit a well-studied system, O${}_2$ dissociation on silver nanoparticles. The nonthermal hot carriers are found to promote molecular dissociation in the low-temperature or high-intensity regime. With increasing laser intensity, the dissociation rate exhibits a transition from a linear to nonlinear dependence due to the onset of vibrational heating as observed in experiment. Our model provides a unified framework to understand the mechanism and dynamics of photocatalysis and reveals the nonthermal pathways for energy harvesting and conversion with surface plasmons.