Design Of Novel Metallic Nanostructures And Research On Their Sensing Properties

With the rapid development of nanotechnology,surface plasmons in metallic nanostructures have currently become one of the most active research topics in the field of physics,information science,materials science,biology,chemistry,and their interdisciplines.Studies on surface plasmons are now growing into a new science,named plasmonics.In this thesis,we first study the optical properties of periodic arrays of metallic nanoparticles(ellipsoidal metallic particles and U-shaped metallic split-ring resonators)lifted by dielectric nanopillars and placed directly on the surface of the substrate.The conditions for the occurrence of diffraction coupling in the periodic array of nanoparticles is also explained.In addition,based on this kind of diffraction coupling effect,we design two high-performance biosensors based on electric SP resonance and magnetic SP resonance.The thesis will mainly elaborate on the following two aspects:1.We demonstrate significantly longer plasmon lifetime and stronger electric field enhancement by lifting the nanoantenna arrays above the substrate by dielectric nanopillars.The role of the pillar is to offer a more homogeneous dielectric background allowing stronger diffraction coupling among plasmonic nanoantennas leading to a Fanolike asymmetric lineshape.It is found that,the electric fields around the nanoantennas can be greatly enhanced when the Fanolike resonance is excited,and a 4.2 times enhancement is achieved compared with the pure resonance in individual nanoantennas.Furthermore,only a collective surface mode with its electric fields of the same direction as the induced electric moment in the nanoantennas could mediate the excitation of such a Fanolike resonance.More importantly,the sensitivity and the figure of merit(FOM)of this plasmonic structure can reach as high as 900 nm/RIU and 53,respectively.Our study offers a new,simple and efficient way to design the plasmonic systems with desired electric field enhancement and spectral lineshape for different applications.2.We report a powerful method to enhance the magnetic plasmon(MP)resonances of metamaterials composed of periodic arrays of U-shaped metallic split-ring resonators(SRRs)for high-quality sensing.We show that by suspending the metamaterials to reduce the effect of the substrate,the strong diffraction coupling of MP resonances can be achieved,which leads to a narrow-band mixed MP mode with a large magnetic field enhancement.It is also shown that for such a diffraction coupling,the magnetic field component of the lattice resonance mode of periodicarrays must be parallel to the induced magnetic moment in the metallic SRRs.Importantly,the sensitivity and the FOM of the suspended metamaterials can reach as high as 1300 nm/RIU and 40,respectively.These results suggest that the proposed metamaterials may find great potential applications in label-free biomedical sensing.