Sharp spectral variations of the ultrafast transient light extinction by bimetallic nanoparticles in the near-UV

TL;DR

This study investigates how bimetallic gold-silver nanocuboids exhibit sharp spectral variations in ultrafast light extinction due to their complex plasmonic modes, with implications for nanophotonics.

Contribution

It provides experimental and theoretical insights into the ultrafast spectral behavior of bimetallic nanoparticles, revealing mode evolution with composition and ultrafast excitation.

Findings

Higher-order modes grow in the near-UV range with increasing Ag-shell thickness

Ultrafast transient extinction shows sharp spectral variations linked to these modes

Theoretical analysis decomposes contributions to the spectral response

Abstract

Noble metal nanoparticles exhibit localized plasmon resonance modes that span the visible and near-infrared spectral ranges and have many applications. Modifying the size, shape, and composition of the nanoparticles changes the number of modes and their properties. The characteristics of these modes are transiently affected when illuminating the nano-objects with ultrashort laser pulses. Here, we synthesize core-shell gold-silver nanocuboids and measure their spectral signature in the stationary and ultrafast transient regimes. Their dipolar transverse mode vanishes with increasing Ag-shell thickness, while higher-order modes grow in the near-ultraviolet range where no plasmon resonance can be generated with single noble metal nanoparticles. These higher-energy modes are associated with sharp spectral variations of the ultrafast transient light extinction by the bimetallic nanocuboids. By carrying out a theoretical investigation, we break down the different contributions to this response and