Enhanced Graphene Plasmonic Mode Energy for Highly Sensitive Molecular Fingerprint Retrieval

Abstract

Graphene plasmons with tightly confined fields and actively tunable resonant frequencies enable the selective detection of molecular vibrational fingerprints with ultrahigh sensitivity, significantly promoting the development of surface‐enhanced infrared absorption spectroscopies (SEIRAS). However, current experimentally obtained enhancements are much smaller than the theoretical prediction due to the extremely low graphene plasmonic mode energy. In this paper, the strategies to improve the mode energy are theoretically and experimentally investigated in a one‐port graphene plasmonic system. By optimizing the Fabry–Pérot cavity length and employing multi‐layer graphene to drive the system into the near critical coupling regime, the localized graphene plasmonic absorptions can be improved from 3% to more than 92%. This induces a 37 times improvement of graphene plasmonic mode energy from 0.4 × 10−13 to 1.5 × 10−12 J per period for the strong plasmon–molecule interactions, enabling the highly sensitive detection of 8 nm thick molecular film. The SEIRAS experimental results demonstrate that a maximum enhancement factor of 162 can be achieved, which is one order larger than that of the reported localized graphene plasmonic sensors. The results showcase the practical usability of localized graphene plasmons for the next‐generation high sensitive nanoscale infrared spectroscopy.

Enhanced Molecular Infrared Spectroscopy Employing Bilayer Graphene Acoustic Plasmon Resonator

“…In order to improve the conversion efficiency of graphene acoustic plasmon, the dielectric spacer layer and gold mirror are further introduced to form an F–P resonance cavity [ 30 , 34 ] to enhance the absorption of graphene plasmons. The total absorption spectrum (see red line) of the proposed graphene plasmonic system is shown in Figure 2 a.…”

“…Our proposed structure can be fabricated with a similar process as previous literature [ 14 , 30 , 34 ]. The main difference of fabrication steps for our AGP biosensor and GP ribbon sensor [ 14 , 34 ] is final continuous graphene sheet transferring. Firstly, the gold reflector can be defined on oxide substrate by photolithography and lift-off.…”

“…Thirdly, a monolayer graphene sheet can be wet-transferred on the top of the optical dielectric spacer and patterned into nano-ribbon arrays with electron beam lithography. For AGP enhanced molecular infrared spectroscopy, a solution of protein sensing analytes can be prepared according to previous work [ 34 ] and spin-coated on the graphene nano-ribbons before transferring the top graphene. The infrared spectra of the device can be acquired with a Fourier-transform infrared spectrometer.…”

Effective Transmission Modulation at Telecommunication Wavelengths through Continuous Metal Films Using Coupling between Borophene Plasmons and Magnetic Polaritons

“…[ 1–3 ] Compared to traditional active bulk materials, the newly emerging 2D layered materials (for instance graphene, [ 4 ] transition metal dichalcogenides, [ 5 ] and black phosphorus [ 6 ] ) exhibit a rich variety of distinctive advantages for optical modulation, including strong light–material interaction, broadband optical response, high nonlinearity, and good compatibility with other photonic structures. [ 7–10 ] Significantly, these 2D materials have been shown to support highly confined and tunable plasmonic modes, [ 11–17 ] showing the ability to manipulate light at the extreme subwavelength scale. This significantly shrinks the size of the modulator and has triggered intense research interest.…”

Facilely Flexible Imprinted Hemispherical Cavity Array for Effective Plasmonic Coupling as SERS Substrate

“…The Raman spectrum has been widely used in qualitative and quantitative analysis as a nondestructive analysis tool, which can provide molecular vibration information [1]. However, the weak signal due to the low Raman cross-section area greatly hinders the development of this technology [2,3].…”