Near field enhancement due to the optical response of small nanoparticles

TL;DR

This study investigates how quantum effects influence the electromagnetic field enhancement around small metallic nanoparticles, revealing significant shifts and underestimations in classical models, with implications for nanoplasmonics.

Contribution

It compares classical and quantum approaches to nanoparticle optical response, highlighting quantum-induced shifts and improved accuracy in near-field enhancement predictions.

Findings

Quantum models show a blue-shift in resonance compared to classical models.

Classical dielectric functions underestimate field amplification.

Results align with experimental data and clarify classical-quantum crossover.

Abstract

In this work we study the strong confinement effects on the electromagnetic response of metallic nanoparticles. We calculate the field enhancement factor for nanospheres of various radii by using optical constants obtained from both classical and quantum approaches and compare their size-dependent features. To evaluate the scattered near-field, we solve the electromagnetic wave equation within a finite element framework. When quantization of electronic states is considered for the input optical functions, a significant blue-shift in the resonance of the enhanced field is observed, in contrast to the case in which functions obtained classically are used. Furthermore, a noticeable underestimation of the field amplification is found in the calculation based on a classical dielectric function. Our results are in good agreement with available experimental reports and provide relevant information on the cross-over between classical and quantum regime, useful in potentiating nanoplasmonics applications.