Abstract
Photonic devices can be developed, and their working principle can be understood only by considering the phenomena taking place at the nanoscale level. Optical properties of plasmonic structures depend on their geometric parameters and are sensitive to them. Recently, many advanced methods for the preparation of nanostructures have been proposed; however still, the geometric parameters are inaccurate. Numerical simulations provide a powerful tool for the analysis of plasmonic nanostructures. To the best of our knowledge, there are not many papers on near-field and far-field properties of single nanoprism and nanoprism dimer, the so-called bowtie, with rounded edges. For this purpose, Finite Integration Technique implemented to the CST Microwave Studio was used. Besides the edge rounding, an additional modification of the resonance modes was investigated, achieved by placement of a spherical nanoparticle in the gap between the prisms. Results of numerical simulations indicate that the radius of the curvature edges strongly affects the plasmon peak localization, and this effect cannot be neglected in plasmonic device design. Increase in the radius of edge curvature causes main extinction cross-section peak blueshift in all cases analyzed. Moreover, our calculations imply that the nanoparticle in the gap between prisms strongly influences the dependence of spectral properties on the radius curvature.
Highlights
Noble metal nanostructures can strongly enhance an electric field upon incident light illumination due to the phenomenon called localized surface plasmon resonance
Numerical studies started with an investigation of the optical properties of a single Ag triangular nanoprism with sharp and rounded edges
Mie theory explains the size dependence of spectral properties of spherical nanoparticles [26], and the optical antenna theory can be successfully applied to describe the optical properties of nanorods [27]. This shift can be explained by decreased charge separation causing an increase in the restoring force, resulting in higher plasmon resonance frequency [8, 17] and phase retardation connected with time delay of reaction of charges on the one side of the particle to the change in charge distribution on the other side [28]
Summary
Noble metal nanostructures can strongly enhance an electric field upon incident light illumination due to the phenomenon called localized surface plasmon resonance. Collective oscillations of quasi-free electrons on the surface of metallic structures and their interactions with molecules lead to the observed surface enhancement of Raman and fluorescence signals [1, 2]. A lot of structures with different shapes have been hitherto theoretically and experimentally investigated, while plasmonic properties strongly depend on the morphology of the nanostructures [3,4,5,6,7,8]. It is not possible to obtain perfect geometric parameters, e.g., sharp edges of nanoprisms or well-defined distance between nanostructures [13]. Theoretical simulations can predict how morphological changes of nanostructures influence their near- and far-field properties. The most common methods are the following: Finite difference time domain method (FDTD), discrete dipole approximation (DDA), and Finite Integration Technique (FIT) [5, 7, 14]
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