Fractal-like plasmonic self-similar material with a tailorable plasma frequency in the near-infrared

TL;DR

This study demonstrates that by adjusting the fractal dimension of nanoporous gold, its plasmonic properties, including plasma frequency, can be precisely tuned across the infrared spectrum, enhancing light-matter interactions.

Contribution

It introduces a method to tailor the dielectric response of fractal-like nanoporous gold through fractal dimension control, enabling customizable plasmonic properties without complex lithography.

Findings

Plasma edge and frequency depend linearly on fractal dimension.

Fractal porous gold exhibits superior plasmonic properties compared to bulk gold.

Longer skin depth (~100-200 nm) allows deep optical energy penetration.

Abstract

In this work, we show that modulating the fractal dimension of nanoporous gold allows its effective dielectric response to be tailored over a wide spectral range of infrared wavelengths. In particular, the plasma edge and effective plasma frequency depend linearly on the fractal dimension, which can be controlled by varying the pore and ligament sizes. Importantly, the fractal porous metal exhibits superior plasmonic properties compared to its bulk counterpart. These properties, combined with a longer skin depth on the order of 100-200 nm, enables the penetration of optical energy deep into the nanopores where molecules can be loaded, thus achieving more effective light-matter coupling. These findings may open new pathways to engineering the optical response of fractal-like or self-similar metamaterials without the need for sophisticated lithographic patterning.