Plasmon excitations in chemically heterogeneous nanoarrays

Kevin Conley, Neha Nayyar, Tuomas P. Rossi, Mikael Kuisma, Volodymyr Turkowski, Martti J. Puska, and Talat S. Rahman

Phys. Rev. B 101, 235132 – Published 11 June 2020

Abstract

The capability of collective excitations, such as localized surface plasmon resonances, to produce a versatile spectrum of optical phenomena is governed by the interactions within the collective and single-particle responses in the finite system. In many practical instances, plasmonic metallic nanoparticles and arrays are either topologically or chemically heterogeneous, which affects both the constituent transitions and their interactions. Here, the formation of collective excitations in weakly Cu- and Pd-doped Au nanoarrays is described using time-dependent density functional theory. The additional impurity-induced modes in the optical response can be thought to result from intricate interactions between separated excitations or transitions. We investigate the heterogeneity at the impurity level, the symmetry aspects related to the impurity position, and the influence of the impurity position on the confinement phenomena. The chemically rich and symmetry-dependent quantum mechanical effects are analyzed with transition contribution maps demonstrating the possibility to develop nanostructures with more controlled collective properties.

Received 18 November 2019
Revised 14 March 2020
Accepted 20 May 2020

DOI:https://doi.org/10.1103/PhysRevB.101.235132

Physics Subject Headings (PhySH)

Plasmonics Quasiparticles & collective excitations

Nanoparticles

Density functional theory

Condensed Matter, Materials & Applied Physics

Authors & Affiliations

Kevin Conley ¹, Neha Nayyar², Tuomas P. Rossi³, Mikael Kuisma⁴, Volodymyr Turkowski², Martti J. Puska ⁵, and Talat S. Rahman ^2,5,*

¹Department of Applied Physics, QTF Centre of Excellence, Aalto University School of Science, P.O. Box 11100, FI-00076 Aalto, Finland
²Department of Physics, University of Central Florida, Orlando, Florida 32816, USA
³Department of Physics, Chalmers University of Technology, SE-412 96 Gothenburg, Sweden
⁴Department of Chemistry, Nanoscience Center, University of Jyväskylä, FI-40014 Jyväskylä, Finland
⁵Department of Applied Physics, Aalto University School of Science, P.O. Box 11100, FI-00076 Aalto, Finland

^*talat.rahman@ucf.edu

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Vol. 101, Iss. 23 — 15 June 2020

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Images

Figure 1
Photoabsorption spectra of weakly doped double-chain arrays. Photoabsorption spectra of a 10 $\times$ 2 (a) and 20 $\times$ 2 (b) double-chain Au array doped with Pd or Cu within the array (off center) compared to that of a corresponding pristine Au array. There is one impurity atom in each chain, and the impurities are nearest neighbors.
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Figure 2
Homogeneous 10 $\times$ 2 Au array. (a) Contributions to the plasmonic excitation at $ω$ = 1.48 eV. The total induced density is shown in the inset and relevant KS orbitals are provided adjacent to the density of states. (b) $λ$ -dependent photoabsorption spectra of the array. The red dots denote the $λ$ -dependent pseudoexcitation energies of two interacting KS transitions ( $ν_{6 \to 7}$ and the HOMO $\to$ LUMO). The partial induced density of each KS transition is shown adjacent to the noninteracting spectrum, and the total induced density of the low-energy excitation is shown adjacent to the spectrum with full interaction. The arrow indicates the photoabsorption mode analyzed in the TCM.
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Figure 3
Homogeneous 20 $\times$ 2 Au array. TCM of the photoabsorption excitations at (a) 1.05 and (b) 2.08 eV. The total induced density of each excitation is shown in the inset and relevant KS orbitals are provided adjacent to the density of states.
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Figure 4
Off-center Cu-doped 10 $\times$ 2 array. There is one impurity atom in each chain and the impurities are nearest neighbors as shown in Fig. 1. (a) Contributions to the doping-induced photoabsorption mode at $ω$ = 1.66 eV. The total induced density is shown in the inset and relevant KS orbitals are provided adjacent to the density of states. (b) $λ$ -dependent photoabsorption spectra of the Cu-doped array. The red arrow indicates the photoabsorption mode analyzed in the TCM. The partial induced density of each KS transition and total induced density of the low-energy excitation are shown adjacent to the noninteracting and fully interacting spectra, respectively. (c) Wave functions of the (5,0) and (7,0) states along the chain axis adjacent to the array in homogeneous and Cu-doped 10 $\times$ 2 Au array (left) and the respective partial transition density in the Cu-doped array (right).
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Figure 5
Off-center Cu-doped 20 $\times$ 2 Au array. There is one impurity atom in each chain and the impurities are nearest neighbors. TCM of the photoabsorption excitations at $ω$ = (a) 0.98 and (b) 1.90 eV. The total induced density of each excitation is shown in the inset and relevant KS orbitals are provided adjacent to the density of states. (c) Noninteracting (dashed line) and fully interacting (solid line) photoabsorption spectra.
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Figure 6
Off-center Pd-doped 20 $\times$ 2 Au array. There is one impurity atom in each chain and the impurities are nearest neighbors. TCM of the photoabsorption excitations at (a) 1.04 and (b) 1.37 eV. The contribution from the circled transition $[ψ (223) \to ψ (234)]$ changes sign between these two excitations. The total induced density of each excitation is shown in the inset. (c) Noninteracting (dashed line) and fully interacting (solid line) photoabsorption spectra. (d) Wave functions of $ψ (223)$ and $ψ (234)$ along the chain axis adjacent to the array (left) and as isosurfaces of the KS orbitals (center) and the respective partial transition density (right).
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