Abstract
Nanoparticles—regularly patterned or randomly dispersed—are a key ingredient for emerging technologies in photonics. Of particular interest are scattering and field enhancement effects of metal nanoparticles for energy harvesting and converting systems. An often neglected aspect in the modeling of nanoparticles are light interaction effects at the ultimate nanoscale beyond classical electrodynamics. Those arise from microscopic electron dynamics in confined systems, the accelerated motion in the plasmon oscillation and the quantum nature of the free electron gas in metals, such as Coulomb repulsion and electron diffusion. We give a detailed account on free electron phenomena in metal nanoparticles and discuss analytic expressions stemming from microscopic (Random Phase Approximation—RPA) and semi-classical (hydrodynamic) theories. These can be incorporated into standard computational schemes to produce more reliable results on the optical properties of metal nanoparticles. We combine these solutions into a single framework and study systematically their joint impact on isolated Au, Ag, and Al nanoparticles as well as dimer structures. The spectral position of the plasmon resonance and its broadening as well as local field enhancement show an intriguing dependence on the particle size due to the relevance of additional damping channels.
Highlights
An accurate description of microscopic properties of metal nanoparticles is important to predict the optical response of e.g., molecules in close proximity to metal surfaces and resulting field enhancement and quenching effects
We present two such semi-classical approaches, the Random Phase Approximation (RPA) and Generalized Nonlocal Optical Response (GNOR), and combine them into a single framework to study their joint impact on MNPs of different materials, sizes and in different environments
We briefly discuss classical electrodynamics and mesoscopic electron dynamics obtained from the RPA and GNOR theories
Summary
An accurate description of microscopic properties of metal nanoparticles (metal NPs—MNPs) is important to predict the optical response of e.g., molecules in close proximity to metal surfaces and resulting field enhancement and quenching effects. Nanoparticles as part of functionalized layers in sensing, spectroscopy [1] and light harvesting applications, photovoltaics [2,3,4,5,6,7] and photocatalysis [8,9,10,11,12], can improve the performance of such devices They are efficient subwavelength scatterers improving the light trapping effect and MNPs provide, in particular, large local fields enhancing charge carrier generation, absorption, and light-induced effects from other nanostructures such as spectral conversion [13] or photoluminescence [14].
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