# Flexible Multilayer Plasmonic Films for Biosensing and Photoemitting Applications

## TL;DR

This paper introduces a flexible plasmonic film that works well for biosensing and enhancing light emission from materials like WS2.

## Contribution

A novel flexible Ag/Al2O3/mica multilayer platform is developed for plasmonic biosensing and photoemission.

## Key findings

- The Ag/Al2O3/mica film shows high refractive index sensitivity for biosensing.
- PL emission of WS2 increases by 16% under bending and shifts by 60 meV/% strain.
- The film remains stable under bending curvatures up to 0.4 mm–1.

## Abstract

Flexible plasmon metasensor devices describe the use
of multiple
Ag/Al2O3/mica layers for tunable plasmonic resonances
and are a promising research direction. Here, we report on a flexible
Ag/Al2O3/mica multilayer platform and its excellent
performance on flexible biosensors and photon-emitting devices. In
our approach, muscovite (mica) was adopted as a single-crystal substrate
due to its optical transparency and mechanical flexibility. The Ag/Al2O3/mica multilayer film is characterized by X-ray
diffraction and transmission electron microscopy. Optical, plasmonic,
and biosensing studies of Ag/Al2O3/mica multilayers
are performed for detailed understanding. A combination of optical
absorption, numerical simulations, and optical reflectance measurements
has confirmed the biosensor performance. Two kinds of flexible plasmonic
device applications are reported here, including (1) plasmonic biosensors
with high refractive index sensitivities and (2) significantly enhanced
spontaneous photoluminescence (PL) of monolayer tungsten disulfide
(WS2) spectra. We found that the PL emission under 0.4
mm–1 curvature bending state increased to 16% compared
to the unbent state and redshift of 60 meV/% strain in the emission
of WS2 monolayer. Furthermore, the Ag/Al2O3/mica multilayer film displays robust stability and strong
endurance up to a bending curvature of 0.4 mm–1.
This study shows great potential to be used for biosensors and flexible
optoelectronics.