Research On The Resonance Model And Sensing Characteristics Of Asymmetric Plasmonic Nanostructures

The asymmetric plasmonic nanostructures can support a series of unique opticalphenomena, such as significant local electromagnetic field enhancement, plasmonicFano resonances and anisotropic optical response. These optical characteristics notonly are used to develop ultra-sensitive single molecule sensing substrates, but alsoapplied in various novel nanophotonic devices. This paper focused on the asymmetriccore-shell plasmonic nanostructures to study the plasmn hybridization effect and thesymmetry breaking by using numerial methods. Moreover, the plasmonic Fanoresonances and anisotropic optical responses are investigated. The Au semishellssensors have been fabricated to measuring the LSPR sensing characteristics.Firstly, the plasmon resonances model was built for semishells. The plasmonhybridization theory is applied to interpret the excitation, shift and slitting of theplasmon resonances of semishells. The calculation results show that the sharp featuresat the ring-tip is the main reason for local field enhancement in semishells. Theintra-particle coupling further enhances the local field. For the tunable plasmon modesand local field enhancement, the semishells can be developed as powerful sensingsubstrates in application of LSPR wavelength-shift sensing and surface-enhancedspectroscopy.Secondly, we used the plasmon hybridization theory to investigate the origin ofthe Fano resonance in core-semishells. The calculation results show that theinteraction between “bright” and “dark” plasmon modes is responsible for theexcitation of Fano resonances. The symmetry breaking of plasmonic nanostructuressignificantly influences the Fano resonance. The tenability of Fano resonances can beaccieved by changing the degree of symmetry breaking in semishell and displacementof the core with respect to the semishell. The local field enhancement induced byplasmon hybridization between the Au core and semishell provides the potentialapplications in biological sensing.Then, we studied the two-dimensional anisotropic optical response of overlappednaoshells. The cavity-ellipsoid model properly explains the unique optical propertiesof the overlapped nanoshells. For the breaking of rotational symmetry, the overlappednanoshells can excite transverse, axial, and longitudinal plasmon resonance modes. The tunable plasmon resonances, the enhanced local fields and the anisotropic opticalproperties suggest that the overlapped nanoshells have potential applications insurface-enhanced spectroscopy and “smart” coating in windows or display devices.Finally, The Au semishell sensing substrates were fabricated by dip coating andion sputtering. The refractive index sensitivity of semishells with different Au shellthicknesses is measured by using solution of different refractive index. The detectionlimit of the sensing substrates is investigated by the layer-by-layer depositon.