[Paper Review] Scattering Suppression and Absorption Enhancement in Contour Nanoantennas

E. Doruk Onal, Kaan Güven|arXiv (Cornell University)|Nov 4, 2015

Plasmonic and Surface Plasmon Research13 references3 citations

TL;DR

This paper proposes a contour nanoantenna design that simultaneously suppresses scattering and enhances absorption in plasmonic dipole nanoantennas by introducing a hollow interior. By reshaping a solid dipole into a contour geometry, scattering drops from 84% to 28% of coupled power while absorption rises from 16% to 72%, transforming the antenna from a scatterer to a strong absorber without altering extinction cross section.

ABSTRACT

The expanding application spectrum of plasmonic nanoantennas demand versatile design approaches to tailor the antenna properties for specific requirements. The design efforts primarily concentrate on shifting the operation wavelength or enhancing the local fields by manipulating the size and shape of the nanoantenna. Here, we propose a design path to control the absorption and scattering characteristics of a dipole nanoantenna by introducing a hollow region inside the nanostructure. The resulting contour geometry can significantly suppress the scattering of the dipole nanoantenna and enhance its absorption simultaneously. Both the dipole and the contour dipole nanoantenna couple to equivalent amount of the incident radiation. The dipole nanoantenna scatters 84% of the coupled power (absorbs the remaining 16%) whereas the contour dipole structure scatters only 28% of the coupled power (absorbs the remaining 72%). This constitutes the transformation from scatter to absorber nanoantenna. The scattering of a contour nanoantenna can be further suppressed by incorporating a lossless dielectric in the hollow region without altering its absorption. We also demonstrate the applicability of scattering suppression and absorption enhancement features of the contour design in other nanoantenna geometries such as the self-assembly compatible nanoantenna structures of nanodisk and nanoring chains. The benefits of the contour design can be readily utilized in diverse applications; including bioplasmonics, medical diagnosis/therapy, cloaked sensing, photovoltaics and thermoplasmonics.

Motivation & Objective

• Address the need for plasmonic nanoantennas with tailored scattering and absorption properties for diverse applications.
• Overcome limitations in existing nanoantenna designs that prioritize either scattering or absorption but not both simultaneously.
• Develop a geometric design strategy to convert a conventional dipole nanoantenna into a high-absorber with minimal scattering.
• Enable low-disturbance sensing in biological environments by minimizing scattering while preserving field coupling.
• Extend the contour design principle to self-assembling nanoantenna systems such as nanodisk and nanoring chains for subwavelength applications.

Proposed method

• Design a contour dipole nanoantenna by introducing a hollow region within a solid dipole structure, maintaining the same overall footprint.
• Use finite-difference time-domain (FDTD) simulations to calculate extinction, scattering, and absorption cross sections across the visible to near-infrared spectrum.
• Define the relative scattering efficiency (RSE) as the ratio of scattering to extinction cross section to quantify scattering suppression.
• Introduce a lossless dielectric material into the hollow region to further suppress scattering without altering absorption.
• Extend the contour geometry to self-assembling systems by replacing solid nanoparticles with nanodisks and nanorings in chain configurations.
• Compare the extinction, scattering, and absorption spectra of dipole, nanodisk chain, and nanoring chain structures to validate performance improvements.

Experimental results

Research questions

• RQ1 Can a geometric modification of a dipole nanoantenna suppress scattering while enhancing absorption simultaneously?
• RQ2 To what extent can scattering be reduced and absorption increased in a plasmonic nanoantenna without changing its extinction cross section?
• RQ3 How does introducing a lossless dielectric into the hollow region affect scattering and absorption in contour nanoantennas?
• RQ4 Can the contour design principle be extended to self-assembling nanoantenna systems like nanodisk and nanoring chains?
• RQ5 What are the implications of this design for applications requiring low-scattering, high-absorption nanoantennas, such as cloaked sensing or thermoplasmonics?

Key findings

• The contour dipole nanoantenna reduces scattering from 84% to 28% of the coupled power, while absorption increases from 16% to 72%, achieving a transformation from scatterer to absorber.
• Extinction cross section remains nearly unchanged, indicating that the total power coupled to the antenna is preserved despite redistribution between scattering and absorption.
• Incorporating a lossless dielectric into the hollow region further suppresses scattering without altering the absorption cross section, enabling additional control over radiation response.
• The nanoring chain structure achieves a relative scattering efficiency (RSE) of 0.28, matching the contour dipole, demonstrating effective scattering suppression in self-assembled systems.
• The nanodisk chain shows an RSE of 0.57, indicating that replacing solid disks with hollow, ring-like geometries significantly reduces scattering compared to solid counterparts.
• The contour design is transferable to various nanoantenna geometries, including self-assembled nanodisk and nanoring chains, enabling deep subwavelength light manipulation and low-scattering operation.