Angstrom-Scale Active Width Control of Nano Slits for Variable Plasmonic Cavity.

Dukhyung Lee,Dai-Sik Kim,Hyeong Seok Yun,Dohee Lee

doi:10.3390/nano11092463

Dukhyung Lee, Dai-Sik Kim + Show 2 more

Open Access

https://doi.org/10.3390/nano11092463

Copy DOI

Abstract

Nanogap slits can operate as a plasmonic Fabry–Perot cavity in the visible and infrared ranges due to the gap plasmon with an increased wavenumber. Although the properties of gap plasmon are highly dependent on the gap width, active width tuning of the plasmonic cavity over the wafer length scale was barely realized. Recently, the fabrication of nanogap slits on a flexible substrate was demonstrated to show that the width can be adjusted by bending the flexible substrate. In this work, by conducting finite element method (FEM) simulation, we investigated the structural deformation of nanogap slit arrays on an outer bent polydimethylsiloxane (PDMS) substrate and the change of the optical properties. We found that the tensile deformation is concentrated in the vicinity of the gap bottom to widen the gap width proportionally to the substrate curvature. The width widening leads to resonance blueshift and field enhancement decrease. Displacement ratio ((width change)/(supporting stage translation)), which was identified to be proportional to the substrate thickness and slit period, is on the order of 10−5 enabling angstrom-scale width control. This low displacement ratio comparable to a mechanically controllable break junction highlights the great potential of nanogap slit structures on a flexible substrate, particularly in quantum plasmonics.

Highlights

Since gap plasmon wavelength is compressed compared to the free space wavelength, a Fabry–Perot cavity for the visible and infrared ranges is established along the thickness direction inside a nanogap slits
We note that the gap width difference between the top and the bottom given by the arc length equation l = rθ is negligible because the metal height is much smaller than the radius of curvature within the simulated range
We demonstrated that the nanogap slit width, and the optical properties of the plasmonic cavity can be controlled actively by applying mechanical bending to the PDMS substrate

Summary

Introduction

Since gap plasmon wavelength is compressed compared to the free space wavelength, a Fabry–Perot cavity for the visible and infrared ranges is established along the thickness direction inside a nanogap slits. Using nanogap slits as a plasmonic cavity, several studies have reported exciting phenomena including enhanced light-matter interaction and resonant transmission [5,6,7,8]. Precise gap width control is a pivotal factor because the resonance properties such as the gap plasmon wavenumber are determined by the gap width. The importance of width control is much more emphasized in the quantum plasmonic regime where tunneling current across a nanogap is exponentially dependent on the barrier width [9,10,11,12,13]

Methods

Results

Discussion

Conclusion