Theoretical Investigation of Plasmonic Properties of Quantum-Sized Silver Nanoparticles
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Theoretical Investigation of Plasmonic Properties of Quantum-Sized Silver Nanoparticles Masoud Shabaninezhad 1 & Guda Ramakrishna 2 Received: 23 July 2019 / Accepted: 4 December 2019 # Springer Science+Business Media, LLC, part of Springer Nature 2019
Abstract Plasmonic nanoparticles (NPs) like silver (Ag) strongly absorb the incident light and produce enhanced localized electric field at the localized surface plasmon resonance (LSPR) frequency. Enormous theoretical and experimental research has focused on the plasmonic properties of the metallic nanoparticles with sizes greater than 10 nm. However, such studies on smaller sized NPs in the size range of 3 to 10 nm (quantum-sized regime) are sparse. In this size regime, the conduction band of the metal particles discretizes, thus altering plasmon properties of the NPs from classical to the quantum regime. In this study, plasmonic properties of the spherical Ag NPs in size range of 3 to 20 nm were investigated using both quantum and classical modeling to understand the importance of invoking quantum regime to accurately describing their properties in this size regime. Theoretical calculations using standard Mie theory were carried out to monitor the LSPR peak shift and electric field enhancement as a function of the size of the bare plasmonic nanoparticle and the refractive index (RI) of the surrounding medium. Comparisons were made with and without invoking quantum regime. Also, the optical properties of metallic NPs conjugated with a chemical ligand using multilayered Mie theory were studied, and interesting trends were observed. Keywords Quantum regime . Multi-layered Mie theory . LSPR . Field enhancement . Absorption . Ligand
Introduction Localized surface plasmon resonance (LSPR) is produced by strong coupling of the incident light and the oscillation of conduction band electrons in metallic NPs [1–3]. This phenomenon leads to strong scattering and absorption of the light as well as significant electric field enhancement around the NPs at LSPR frequency [4]. These optical properties, which resulted from the LSPRs of metallic NPs, have found applications in the fields of photonics [5–14], medicine [6, 15–18], biological imaging [5, 6, 19, 20], biosensing [21–30], plasmonic resonance energy transfer (PRET) [7–9], fluorescence Electronic supplementary material The online version of this article (https://doi.org/10.1007/s11468-019-01102-9) contains supplementary material, which is available to authorized users. * Masoud Shabaninezhad [email protected] 1
Department of Physics, Western Michigan University, 1903 Western Michigan Avenue, Kalamazoo, MI 49008, USA
2
Department of Chemistry, Western Michigan University, 1903 Western Michigan Avenue, Kalamazoo, MI 49008, USA
enhancement [10, 22], and surface-enhanced Raman scattering (SERS) [11, 12]. Also, it was shown that plasmonic NPs can transfer the extra heat to the surrounding medium through electron-electron, electron-phonon, and phonon-phonon interactions [31–33], which can be applied for
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