Quantum Confinement Effects on the Near Field Enhancement in Metallic Nanoparticles

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.

Strong enhancement of direct transition photoluminescence at room temperature for highly tensile-strained Ge decorated using 5 nm gold nanoparticles

“…For example, a redshift was observed in GNP embedded in a high-index contrast material, which is consistent with the observation in this study [50]. On the other hand, for small size NP, a blue-shift in the main resonance has been observed due to the quantum effect of size reduction [53,54]. These two competing effects result in a 15 nm redshift in the calculated main resonance peak.…”

Probing Nanoparticle Plasmons with Electron Energy Loss Spectroscopy

“…When the size of the nanoparticles, or the distance between metallic constituents, is smaller than a few nanometers, the experimentally observed LSPR behavior deviates from the context of classical electrodynamics, and in these cases, a quantum treatment of the resonance electrons is necessary. The deviation from classical electromagnetic theory may arise from the electron energy discretization due to quantum confinement and the associated modification of the dielectric properties, the spill-out of electrons beyond the nanoparticle surface, and the electron screening effect. ,, The inclusion of quantum effects in small nanoparticles leads to a significant shift in the LSPR resonance energy and differences in the electric field enhancements − when compared to the classically calculated quantities. The quantum size effect in small metallic nanoparticles was first explored by Kubo and Kawabata in the 1960s by considering electron energy discretization. , Then in 1975, Ganière et al predicted a blue-shift in the absorption of small spherical nanoparticles (<10 nm in size) that could not be accounted for in classical simulations.…”

Green Synthesis of Fe3O4/Chitosan Nanoparticles Utilizing Moringa Oleifera Extracts and Their Surface Plasmon Resonance Properties

“…Thus, SPR signal properties depend on the size of nanoparticles. 90 In addition to the effect of particle size, the different surface densities of CS on the Fe 3 O 4 nanoparticles, as illustrated in Fig. 9, also contribute to the change in the refractive index of the nanoparticles, causing a larger shift in the SPR angles.…”