Graphene Salisbury Screen Terahertz Absorber Design And Fabrication Research

With the rapid development of terahertz technology,terahertz radar,terahertz imaging,terahertz detectors and other terahertz-related electronic components have been widely used in current technology.In order to more effectively shield the effects of terahertz signals,improving the environment for the propagation of terahertz information and ensuring the normal operation of more sophisticated electronic equipment.The study of terahertz absorbing materials with wide band and strong absorption in the terahertz band is particularly important,and the development of terahertz absorbers has become a new hot spot for scientific research.Sandwich-type structure based on Salisbury screen effect is a simple and effective strategy to acquire high-performance THz absorption.Traditional metal/insulant/metal(M/I/M)absorber is difficult to construct multilayer structure because of low light transmittance of the surface metal film.Graphene is the preferred material for terahertz absorber due to its ultra-strong electron mobility,excellent optical transparency,extremely high Young’s modulus and surface plasmon resonance properties in terahertz waves.This paper proposes an innovative terahertz absorber based on the Salisbury shielding effect of graphene,which integrates the excellent optoelectronic properties of graphene and overcomes the problem of preparing multilayer composite structures.This absorber breaks through the bottleneck of traditional absorber cumbersome preparation process,narrow absorption band,and poor substrate compatibility.The absorption mechanism of graphene Salisbury screen absorber and terahertz wave response law are investigated.Ultimately,graphene absorbers with broadband and efficient absorption are obtained.The main research is as follows:1.COMSOL Multiphysics finite element method is used to perform single-layer graphene Salisbury screen absorber design and performance simulations.Numerical simulation results show that the field intensity distribution in the air region is more homogeneous indicating that the absorber has well-matched characteristics with the free-space impedance.Moreover,the variation of the dielectric layer thickness can change the stroke of the absorber,thus increasing the number of resonance peaks.The increase in the number of graphene stacked layers can enhance the coupling between the absorber and the incident electromagnetic wave,with a significant increase in absorption performance.Finally,the experimental test results show well agreement between numerical simulation and experiment.The absorbers prepared by simple stacked graphene/polyimide/graphene/--polyimide/graphene/polyimide/gold structures achieved over 81%absorption in the frequency range of 0.25 to 2.25 THz with a relative bandwidth of 160%and a maximum absorption of 100%.2.Based on the few-layer graphene having higher chemical stability and better controllability,the FLG based Salisbury absorber absorption performance is investigated.The study of the mechanism of the change of the photoelectric properties during the interfacial treatment of few-layer graphene shows that the graphene surface is modified by oxygen atoms causing the appearance of a large number of sp~3 bonded carbon atoms and defective states.In this process,it is found that the stable sp~2 stable lattice structure of FLG transformed to sp~3 amorphous carbon,which disrupts the carrier transport between sp~2networks and leads to the gradual degradation of electrical properties.The results of terahertz time-domain spectroscopy tests show that the graphene film etching time has a significant effect on the absorption performance of the few-layer graphene Salisbury screen absorber.With the increase of etching time,the absorption bandwidth is first increasing and then decreasing.The absorption bandwidth reaches the maximum of 0.60～1.04 THz under the etching 1 min condition.By further increasing the etching time,the absorption peak gradually becomes sharper.The above results show that the absorption performance of the few-layer graphene Salisbury screen absorber can be tuned by controlling the oxygen plasma etching time,which has important theoretical implications for the study of graphene optical devices.