Inverted Temperature Gradients in Gold-Palladium Antenna-Reactor Nanoparticles

TL;DR

This study reveals an inverted temperature gradient in gold-palladium nanoparticle systems, where palladium satellites concentrate photothermal energy, creating a localized heat hotspot that enhances catalytic activity.

Contribution

The paper demonstrates a novel inverted temperature gradient in bimetallic nanoparticles, showing palladium satellites heat up significantly more than the gold core after excitation.

Findings

Palladium satellites reach 180 K higher temperature than gold core

Strong inverted temperature gradient opposes energy input direction

Enhanced heat localization at palladium nanosite

Abstract

In addition to enhanced fields and possible charge transfer, the concentration of photothermal energy at the nanoscale is a foundation of plasmon-driven photochemistry. We demonstrate a further enhancement of heat localization during the dissipation of energy in a bimetallic antenna--reactor system with palladium satellites attached to a gold nanoparticle. After pulsed excitation of the gold core, the satellites collect nearly all photothermal energy and heat up by 180\,K while the light-absorbing gold core remains much colder. By comparing transient absorption dynamics of a series of bimetallic nanoparticles with a three-temperature model, we can precisely assess the temperatures of the electronic and vibrational subsystems. We find a strong inverted temperature gradient that opposes the direction of energy input and concentrates the light energy at the active catalytic nanosite.