Abstract
The discrete dipole approximation (DDA) is used to model the absorption efficiency of isolated gold (Au) and silver (Ag) ellipsoidal nanoparticles. The characteristics of the plasmonic bands of those nanostructures depend strongly on the size and orientation of the particles in both the lab and target frames. At specific rotation and incident angles, the desired plasmonic mode can be excited. The result of the simulation shows the possibility of excitation of three plasmonic modes—one longitudinal mode (LM) and two transverse modes (TM)—corresponding to the redistribution of the polarization charges along each principal axis. At oblique incidence of the incoming light, both the Au LM and a hybrid Au TM are observed whereas three more distinct plasmonic modes can be found in the case of the Ag particle. The effect of length distribution on the characteristics of the plasmonic bands is also examined for the three principal axes. The band position of the plasmonic bands associated with the electronic oscillation along each principal axis is found to vary linearly with the axis length. The linear variation of the band position of the LM is steeper as compared with the one found for the other modes.
Highlights
The localized surface plasmon resonance (LSPR) is the electronic oscillatory motion in the conduction band of the metallic nanostructure [1, 2]
All the discrete dipole approximation (DDA) calculations presented here refer to air as the surrounding material where the ellipsoidal nanoparticle is embedded
The optical response of the metallic ellipsoidal nanoparticle is quite specific when compared to other nanoparticle morphologies due to the possibility of three different LSPR modes
Summary
The localized surface plasmon resonance (LSPR) is the electronic oscillatory motion in the conduction band of the metallic nanostructure [1, 2]. To better appreciate the behavior of particles of this specific and quite interesting shape, the current work aims at studying in a comprehensive way the optical properties of an oriented isolated nanoellipsoidal particle both for the gold (Au) and silver (Ag) cases since these two materials in nanoparticle form exhibit most interesting selective absorption in the visible and near-infrared range It would be of great interest to find whether there exist combinations of the rotation and orientation angles that can allow the simultaneous excitation of all PMs for Au and Ag nanoellipsoids. To this end the effect of different parameters on the optical response of the Au and Ag nanoparticles will be discussed These parameters include the orientation of the target in both the lab and the target frames and the sensitivity of the band position of the PM to the length distribution of each principal axis. The open-source Fortran-90 software package (DDSCAT 7.1) was used to calculate the absorption cross-section
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