Hot-carrier generation in bimetallic Janus nanoparticles

TL;DR

This work presents a multi-scale atomistic framework that couples macroscopic Maxwell electrodynamics with large-scale tight-binding models to study hot-carrier generation in bimetallic Janus nanoparticles (Ag–Au, Ag–Cu, Au–Cu). It reveals that spherical Ag–Au Janus structures exhibit the strongest hot-carrier production due to distinct LSP resonances, while dumbbell geometries amplify generation via neck-region field confinement and polarization-tuned coupling. The findings show significant enhancement of hot-carrier yields with increasing neck size, particularly for Ag–Au and Au–Cu, and highlight interband and intraband contributions that shape electron vs. hole generation at specific resonances. The results provide mechanistic guidance for designing Janus nanoparticle–based photocatalytic and photonic devices with interface hot spots and tailored spectral responses.

Abstract

Energetic electrons and holes generated from the decay of localized surface plasmons in metallic nanoparticles can be harnessed in nanoscale devices for photocatalysis, photovoltaics or sensing. In this work, we study the generation of such hot carriers in bimetallic Janus nanoparticles composed of Au, Ag and Cu using a recently developed atomistic modelling approach that combines a solution of the macroscopic Maxwell equation with large-scale quantum-mechanical tight-binding models. We first analyze spherical Janus nanoparticles whose unique hot-carrier spectrum can be associated with the spectra of the two hemispheres and the interface coupling and find that under solar illumination the Ag-Au system exhibits the highest hot-carrier generation rate. For dumbbell-shaped Janus nanoparticles, we observe a significant increase in hot-carrier generation with increasing neck size. This is caused by a dramatic enhancement of the electric field in the neck region. We also study the dependence of hot-carrier generation on the light polarization and find that the largest generation rates are obtained when the electric field is perpendicular to the interface between the two metals due to the maximal dipole coupling with the electric field. The insights from our study will guide the experimental design of efficient hot-carrier devices based on bimetallic Janus nanoparticles.

Figures (6)

• Figure 1: (a)-(d): Schematic illustration of the geometry of Janus nanoparticles studied in this work: a spherical Janus nanoparticle (a) and dumbbell-shaped Janus nanoparticles with different neck sizes $d$ (b)-(d). (e): Schematic illustrating the definition of the light polarization vector.
• Figure 2: Total generation rate of highly energetic electrons (red solid line) and hot holes (blue dashed line) as function of photon energy for spherical Janus nanoparticles with different compositions (Ag-Au, Ag-Cu and Au-Cu). Highly energetic carriers are defined as having energies larger than 1 eV relative to the Fermi level. (a): Results for light polarization perpendicular to the interface ($\theta=0^\circ$). (b): Results for light polarization parallel to the interface ($\theta=90^\circ$).
• Figure 3: Energetic distribution of hot electrons (red lines) and hot holes (blue lines) in spherical Janus nanoparticles at the localized plasmon resonance frequencies, see Fig. \ref{['fig:freq_dep']}. The electric field is perpendicular to the interface between the metals ($\theta=0^\circ$). For Janus nanoparticles containing Cu, the total generation rates of highly energetic electrons and holes only exhibit a single peak and we instead show the energetic distributions at the absorption onset of Cu at 2.1 eV. All energies are relative to the Fermi level.
• Figure 4: Total generation rate of (a) highly energetic electrons and (b) and highly energetic holes of Ag-Au, Ag-Cu and Au-Cu Janus nanoparticles as function of neck size $d$ under solar illumination. Highly energetic carriers are defined as having energies larger than 1 eV relative to the Fermi level. The electric field is perpendicular to the interface ($\theta=0^\circ$).
• Figure 5: (a): Total generation rate of highly energetic electrons (red solid line) and holes (blue dashed line) as function of photon energy for Ag-Au Janus nanoparticles with different neck sizes. Highly energetic carriers are defined as having energies larger than 1 eV relative to the Fermi level. (b): Energetic distribution of hot electrons (red lines) and hot holes (blue lines) in Ag-Au Janus nanoparticles with different neck sizes at the lower-energy localized plasmon resonance frequencies. All energies are relative to the Fermi level. The light polarization is $\theta=0^\circ$.