Generation of plasmonic hot carriers from d-bands in metallic nanoparticles.

Lara Román Castellanos,Ortwin Hess,Johannes Lischner,Juhan Matthias Kahk

doi:10.1063/5.0003123

Abstract

We present an approach to master the well-known challenge of calculating the contribution of d-bands to plasmon-induced hot carrier rates in metallic nanoparticles. We generalize the widely used spherical well model for the nanoparticle wavefunctions to flat d-bands using the envelope function technique. Using Fermi's golden rule, we calculate the generation rates of hot carriers after the decay of the plasmon due to transitions either from a d-band state to an sp-band state or from an sp-band state to another sp-band state. We apply this formalism to spherical silver nanoparticles with radii up to 20 nm and also study the dependence of hot carrier rates on the energy of the d-bands. We find that for nanoparticles with a radius less than 2.5 nm, sp-band state to sp-band state transitions dominate hot carrier production, while d-band state to sp-band state transitions give the largest contribution for larger nanoparticles.

Highlights

There is currently significant interest in the properties of plasmon-induced hot carriers in metallic nanostructures
We present an approach to master the well-known challenge of calculating the contribution of d-bands to plasmon-induced hot carrier rates in metallic nanoparticles
The rate exhibits a peak at the localized surface plasmon energy, hωLSP = 3.65 eV, as a result of the strong localized surface plasmons (LSPs)-induced enhancement of the electric field

Summary

Introduction

There is currently significant interest in the properties of plasmon-induced hot carriers in metallic nanostructures. Such nanostructures absorb sunlight by generating localized surface plasmons (LSPs) that can decay into electron–hole pairs via the Landau damping mechanism. Most experiments employ traditional plasmonic metals, such as Ag or Au, as these materials exhibit strong plasmonic resonances in their absorption spectrum. The electronic structure of these materials is characterized by a dispersive band of mixed s- and p-state character (referred to as the sp-band), which crosses the Fermi level and multiple occupied d-bands with a comparably flat dispersion.. If the d-bands are sufficiently close to the Fermi energy, it is possible to excite electrons from the d-bands into the sp-band.. The electronic structure of these materials is characterized by a dispersive band of mixed s- and p-state character (referred to as the sp-band), which crosses the Fermi level and multiple occupied d-bands with a comparably flat dispersion. If the d-bands are sufficiently close to the Fermi energy, it is possible to excite electrons from the d-bands into the sp-band. For example, Barman and co-workers measured a photocurrent arising from hot d-band holes in gold nanoparticles, but the relative importance of such d-to-sp transitions compared to transitions between sp-band states in nanoparticles has not yet been studied in detail

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Results

Conclusion