Microscopic Electron Dynamics in Metal Nanoparticles for Photovoltaic Systems

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.

Thin Films of Nonlinear Metallic Amorphous Composites

“…A further difficulty with homogenization could be waveguiding effects arising in the host material that are suppressed in EMTs. Another interesting aspect is the influence of finite-size effects in ultra-small metal nanoparticles, such as a nonlocal optical response, which can be addressed with semi-classical theories [37][38][39] and ab initio methods [40,41]. This typically yields shifts in the LSPR position, directly impacting the nonlinear susceptibility and, in addition, is accompanied by the nonlocal quenching of the local fields overall reducing local intensities found in the classical picture.…”

Spatial nonlocality effect on the surface plasmon propagation in plasmonic nanospheres waveguide

“…According to Matthiessen's rule, the total damping rate in a small nanosphere is given by [39][40][41][42][43],…”

Mode Splitting Induced by Mesoscopic Electron Dynamics in Strongly Coupled Metal Nanoparticles on Dielectric Substrates

“…In recent years, experiments to verify effects stemming from the quantum nature of free electrons in metals [70,71,72] were made and theories pursued the extension of classical electrodynamics to scalable, semi-classical descriptions. In particular, a description of Lorentz friction in metals from Random Phase Approximation (RPA) [65,73], i.e., the loss of energy in the collective motion of electrons due to acceleration in the plasmon oscillation [53,54,65], and short-ranged electron–electron interactions, such as the Coulomb force and diffusion, via the Generalized Nonlocal Optical Response model (GNOR) based on coupling the hydrodynamic equation for an electron plasma to the electromagnetic wave equation for bound electrons [52,74,75] was introduced. Such nonlocal effects are inherently nonlinear and have been reviewed with respect to nonlinear phenomena in Ref.…”

“…In particular, the particle size and interaction volume in the systems under study, see Figure 1A, reach down to only a few nanometers. Due to this spatial confinement in the metal nanostructures, it is necessary to account for short-ranged electron–electron interactions and include aspects of mesoscopic, light-induced electron dynamics [50,51,52,53,54]. However, most numerical models rely on the classical description of metals using a frequency-dependent permittivity, thus neglecting effects arising from quantum confinement.…”