Bowtie nanoantenna driven by a Yagi-Uda nanoantenna: a device for plasmon-enhanced light matter interactions

Abstract

We propose a plasmonic device, based on the combination of a Yagi-Uda nanoantenna and a bowtie nanoantenna, that can enable on-chip implementation of plasmon-enhanced light-matter interaction processes such as surface-enhanced Raman scattering (SERS), surface-enhanced infrared absorption spectroscopy, and plasmon-enhanced fluorescence. In this device, a localized source is employed to excite the Yagi-Uda nanoantenna, which in turn drives the bowtie nanoantenna. We employ finite difference time domain (FDTD) method to perform numerical simulations to obtain radiation characteristics of the Yagi-Uda nanoantenna as well as the electric field enhancements in the vicinity of the bowtie nanoantenna excited by the Yagi-Uda nanoantenna. We find that for a wavelength of 785 nm, an electric field enhancement of ∼ 196 can be achieved in between the arms of the bow-tie nanoantenna even when the minimum gap between nanostructures is as large as 10 nm. It is found that this electric field enhancement is significantly large when compared with the maximum electric field enhancement (∼ 11) obtained for direct excitation of the bowtie nanoantenna by a point source or with the maximum electric field enhancement (∼ 34) obtained for plane wave excitation of the bowtie nanoantenna. As the electromagnetic enhancement of SERS can be approximated to be the fourth power of the electric field enhancement, SERS electromagnetic enhancement of ∼ 1.5 × 109 is achieved for the bow-tie nanoantennas excited by the Yagi-Uda nanoantennas, even when the minimum gap between the arms of the bow-tie nanoantenna is as large as 10 nm. We also analyze the effect of various geometrical parameters of the nanoantennas and show that the maximum electric field enhancement at a given wavelength can only be obtained when both the Yagi-Uda nanoantenna and the bowtie nanoantenna are resonant at that wavelength. Moreover, we calculate the electric field enhancements at different near-infrared wavelengths. Employing the proposed device, an electric field enhancement of ∼ 945 is obtained at a wavelength of 1500 nm resulting in a SERS electromagnetic enhancement factor as high as ∼ 8 × 1011, even when the minimum gap between nanostructures is as large as 10 nm.