Terahertz Metal-Graphene Hybrid Metamaterials And Its Biosensing Applications

Terahertz technology is a reliable label-free and speedy method which holds great potential in biosensor applications.However,when the measured sample amount is very small,it cannot interact sufficiently with the terahertz electromagnetic waves,inducing negligible changes in the response and making detection extremely difficult or even impossible with conventional techniques.In this thesis,metamaterials are emerged as an alternative way to overcome this limitation.Metamaterials can be defined as artificial materials whose electromagnetic properties can be controlled by the shape and geometry.Metamaterials can produce a strong field concentration at localized spots under an external source illumination.This huge field confinement enhances interaction between light and analyte,giving rise to a strong change in the spectral response.Graphene,consisting of sp~2hybridized carbon atoms,becomes one of the most promising nano-platforms in the field of biosensing due to good biocompatibility and excellent physical properties.In this thesis,the applications of metal-graphene hybrid metamaterials in terahertz band are studied by CST simulation,terahertz time domain spectroscopy,AFM imaging and Raman spectroscopy.In the first project,metallic slits and graphene ribbons were used to compose hybrid metamaterials.The structural parameters were optimized for observation of Rabi splitting under terahertz excitation.The sensitivity of the device is characterized by analyzing the peak shift of the transmission spectrum of the metamaterial with the change of carrier concentration.The results show that the sensitivity of the device can reach 325 electron or hole doping per square micron.In the second project,considering that patterned graphene will reduce the performance of graphene,a hybrid metamaterial basing on whole graphene was proposed.The structure was prepared by photolithography and etching,and characterized by terahertz time domain spectrometer.The strong coupling between metallic slits and graphene was successfully realized.The hybrid metamaterial can be used to monitor three different aggregation phases of Aβ (16-22) peptide including lag phase,elongation phase and steady phase,and the reliability of the results is verified by AFM and Raman.Our designed metal-graphene hybrid metamaterial successfully acts as a high sensitivity sensor to monitor the aggregation behavior of Aβ (16-22) peptides.