Surface plasmon resonance spectroscopy of single bowtie nano-antennas using a differential reflectivity method

TL;DR

This study investigates the structural and optical properties of individual bowtie nanoantennas on glass and GaAs substrates, revealing high uniformity and tunable plasmonic resonances through differential reflectivity spectroscopy.

Contribution

It demonstrates a high-precision fabrication and optical characterization method for single nanoantennas, enabling detailed analysis of their plasmonic properties and inter-particle coupling.

Findings

Nanoantennas on glass show narrower size distribution than on GaAs.

Resonance linewidth decreases from 0.21 eV to 0.07 eV with size reduction.

Strong polarization dependence indicates effective inter-particle coupling.

Abstract

We report on the structural and optical properties of individual bowtie nanoantennas both on glass and semiconducting GaAs substrates. The antennas on glass (GaAs) are shown to be of excellent quality and high uniformity reflected by narrow size distributions with standard deviations for the triangle and gap size of $\sigma_s^{glass}=4.5nm$ ($\sigma_s^{GaAs}=2.6nm$) and $\sigma_g^{glass}=5.4nm$ ($\sigma_g^{GaAs}=3.8nm$), respectively. The corresponding optical properties of individual nanoantennas studied by differential reflection spectroscopy show a strong reduction of the localised surface plasmon polariton resonance linewidth from $0.21eV$ to $0.07eV$ upon reducing the antenna size from $150nm$ to $100nm$. This is attributed to the absence of inhomogeneous broadening as compared to optical measurements on nanoantenna ensembles. The inter-particle coupling of an individual bowtie nanoantenna, which gives rise to strongly localised and enhanced electromagnetic hotspots, is demonstrated using polarization-resolved spectroscopy, yielding a large degree of linear polarization of $\rho_{max}\sim80\%$. The combination of highly reproducible nanofabrication and fast, non-destructive and non-contaminating optical spectroscopy paves the route towards future semiconductor-based nano-plasmonic circuits, consisting of multiple photonic and plasmonic entities.