Atomistic Theory of Plasmon-Induced Hot-carriers in Al Nanoparticles

TL;DR

The paper tackles how localized surface plasmons in aluminum nanoparticles generate hot carriers and how this behavior differs from noble metals. It introduces a hybrid method that couples a macroscopic Maxwell solver with large-scale atomistic tight-binding simulations to compute hot-carrier generation via Fermi's golden rule for spheres up to $D=10$ nm. The study finds that hot-carrier distributions in AlNPs are nearly energy-independent across the accessible range at LSP excitation, with interband processes and band-structure effects shaping high-energy channels, unlike Au/Ag. Hot-carrier rates depend on nanoparticle size and the surrounding dielectric environment, with LSP energy tunable from $ω_{LSP}$ around $9.0$ eV (ε_m=1) down to $2.0$ eV (ε_m=30), suggesting opportunities for earth-abundant, UV-tuned hot-carrier devices. These insights imply potential impact in photodetection, photocatalysis, and energy harvesting, enabling scalable aluminum-based plasmonics.

Abstract

Hot electrons and holes generated from the decay of localized surface plasmons (LSPs) in aluminum nanostructures have significant potential for applications in photocatalysis, photodetection and other optoelectronic devices. Here, we present a theoretical study of hot-carrier generation in aluminum nanospheres using a recently developed modelling approach that combines a solution of the macroscopic Maxwell equation with large-scale atomistic tight-binding simulations. Different from standard plasmonic metals, such as gold or silver, we find that the energetic distribution of hot electrons and holes in aluminium nanoparticles is almost constant for all allowed energies. Only at relatively high photon energies, a reduction of the generation rate of highly energetic holes and electrons close to the Fermi level is observed which is attributed to band structure effects suppressing interband decay channels. We also investigate the dependence of hot-carrier properties on the nanoparticle diameter and the environment dielectric constant. The insights from our study can inform experimental efforts towards highly efficient aluminum-based hot-carrier devices.

Figures (4)

• Figure 1: Quasistatic absorption cross-sections $C_{abs}$ of spherical Al nanoparticles with 10 nm diameter, embedded in environments with dielectric constants $\epsilon_m=$ 1, 5, 10, 15, and 30.
• Figure 2: (a) Density of states of spherical aluminum nanoparticles of diameters $D$$=$ 2 nm, 4 nm, and 10 nm from tight-binding. (b) Band structure of bulk Al obtained from a tight-binding calculation.
• Figure 3: Hot-carrier generation rates of spherical Al nanoparticles with different diameters $D$ in different dielectric environments. For each environment, the generation rate is calculated at the corresponding LSP energy. (a): $\epsilon_m = 1$ and $\omega_{LSP}=9.0$ eV; (b): $\epsilon_m = 10$ and $\omega_{LSP} = 3.4$ eV; (c): $\epsilon_m = 30$ and $\omega_{LSP} = 2.0$ eV.
• Figure 4: Hot-carrier generation rates of spherical Al nanoparticles for photon energies of $1.5, 2.0, 4.0 \, \text{eV}$(a) and $6.0, 7.0$ and $8.0 \, \text{eV}$(b). Results were obtained for nanoparticles with a diameter of 4 nm, immersed in a medium with dielectric constant $\epsilon_m$ = 30. The brackets highlight energy windows near the Fermi level in which very few electrons are generated.