Ultrafast interband transitions in nanoporous gold metamaterial

TL;DR

This study reveals that nanoporous gold exhibits unique ultrafast electronic responses, supporting lower energy interband transitions and efficient hot carrier generation, differing significantly from continuous gold films.

Contribution

It demonstrates how nanoscale porosity in gold alters ultrafast electronic dynamics, introducing a platform for tunable electronic properties not found in bulk materials.

Findings

Nanoporous gold supports lower energy interband transitions.

Enhanced hot carrier generation in nanoporous gold.

Ultrafast dynamics align with the two-temperature model.

Abstract

Nanoporous metals have emerged as promising functional architectures due to their tunable optical and electronic properties, high surface areas, and versatile use in real-life applications such as sensing, catalysis, and biomedicine. While the optical and morphological properties of nanoporous metals have been extensively studied, their electronic properties at ultrafast timescales remain largely unexplored. Here, we study the transient response of a nanoporous gold metamaterial and compare it with the ultrafast dynamics of a continuous gold film. We unravel that the nanoporous sample supports lower energy interband transitions, due to a much higher electron temperature in the nanoporous material, which causes an enhanced redistribution of electron density around the Fermi level. The experimental results are consistent with the two-temperature model, which highlights the role of nanoscale porosity in enabling the more efficient generation of hot carriers, thus allowing lower energy photons to induce interband transitions. Our findings demonstrate that nanoporosity affects fundamental ultrafast electronic processes and introduces this platform as temporal metamaterial allowing the emergence of tunable electronic properties not supported by the bulk counterpart. Furthermore, we present new insights into ultrafast electronic properties of nanoporous metals, which can impact several areas, from photochemistry and catalysis to energy harvesting and opto-electronics.