Probing Composite Vibrational Fingerprints in the Terahertz Range With Graphene Split Ring Resonator

Xinrong Mao,Jinfeng Zhu,Jianming Zhuo,Yanfen Hang,Yuanguo Zhou,Yijun Cai,Qiang Ren

doi:10.1109/jphot.2020.3017375

Abstract

Sensors with single resonant mode often produce false positive when detecting the composite vibrational fingerprints of molecules in the terahertz (THz) range. In this study, a multi-resonant plasmonic structure, consisting of periodic graphene split ring resonator (SRR) arrays, is proposed for THz sensing. The effective detection of ultrathin (0.1 μm) lactose layer is given as an example to demonstrate the detection sensitivity. The vibrational fingerprints of lactose at 0.53 THz and 1.37 THz are enhanced in transmission spectra. Besides, resonant frequencies could be actively adjusted with the gate voltage applied on the SRR array. The physical mechanism of multi-resonance can be explained by a combination of LC resonance and dipole resonance of the structure, which can be observed in the electric field distributions. Moreover, the sensing performance can be further optimized by varying geometric parameters. Furthermore, the refractive index sensing performance of the sensor is also investigated by altering the surrounding medium on the surface. The designed sensor can work under an oblique incidence, which provides potential applications in biological analysis and medical diagnostics.

Highlights

Terahertz (THz) wave has wide application prospects in the field of sensing due to its unique properties, such as transparency in most media, non-ionization characteristics, and low photon energy [1]–[3]
We numerically study a multi-resonant sensor based on graphene split ring resonator (SRR) metasurface, which can be utilized to realize fingerprint detection in the THz range
We have designed a plasmonic structure for THz sensing using periodic graphene SRR, whose resonances can be tuned by electrostatic gating

Summary

Introduction

Terahertz (THz) wave has wide application prospects in the field of sensing due to its unique properties, such as transparency in most media, non-ionization characteristics, and low photon energy [1]–[3]. A large volume of samples are often required to identify specific molecules To overcome this limitation, it is necessary to enhance the interaction between light and molecules, improving the sensitivity of the THz detection technology. In order to obtain obvious vibrational signal with a small volume of samples, researchers utilized microstructures or nanostructures to enhance the local electric field for improving the detection sensitivity. The plasmonic resonances were dynamically adjusted by applying bias voltage on graphene so as to selectively overlap with different vibrational bands of proteins. All of the graphene-based sensors mentioned above have an individual resonance, showing limitation in identifying spectrally separated vibrational fingerprints of molecules. We numerically study a multi-resonant sensor based on graphene SRR metasurface, which can be utilized to realize fingerprint detection in the THz range. The influence of the incident angle and polarization angle on the sensing performance will be discussed

Modeling and Methods

Results and Discussion

Conclusion