The Sensitivity Investigation Of LSPRs Sensor Based On The Au@Cu_2-xS Nanoparticle

The Localized Surface Plasmon Resonances?LSPRs?of core-shell structure nanoparticles?CSNs?has become a hot research topic in nanometer photonics at present.The CSNs LSPRs exhibit the excellent sensitivity performance as the structure of the nanoparticle and refractive index?RI?of surrounding medium change compared with that of the ordinary single structure of noble metal nanoparticles.However,the resonance frequency of these CSNs still cannot cover the entire near-infrared region because the resonance wavelength of the metal shell is concentrated in visible light,which plays a more important role in influencing the optical properties of CSNs.In this paper,we present a new type of LSPR sensor based on metal-semiconductor CSNs that show a wide resonance frequency band by controlling the semiconductor with appreciable free carrier concentrations.In addition,due to the optical properties of metal core and semiconductor shell,there are two LSPRs in different light regions supported by the metal core and semiconductor shell,respectively.The result is the greatly increased red-shift of LSPR peak,the broadened resonance wavelength,which could greatly improve sensitivity.Based on the extended Mie scattering theory and the Comsol multiphysics 5.2a simulation software,taking Au@Cu_2-xS CSNs as an example,we can tune the resonance wavelengths of CSNs to cover the entire near-infrared band by varying their geometrical parameters.Compared with other CSNs,the Au@Cu_2-xS CSNs can not only increase the red-shift of LSPRs peak and broaden the resonance wavelength,but also improve the RI sensitivity and widen LSPR sensors'applications.The reason is that the oscillations of the same type of charge on the outer and inner shell surfaces of Au@Cu_2-xS CSNs caused by dual LSPRs,resulting in the decrease of the surface restoring force and the increase of LSPRS sensing sensitivity during the increase of the shell.On the basis of this,the sensitivity characteristics of Au@Cu_2-x-x S nanorods are studied.We found that the sensitivity can be improved effectively by increasing the ratio of the length to diameter and the core to the shell of Au@Cu_2-xS nanorods.The reason is very similar to that of Au@Cu_2-xS CSNs.In addition,under the same section,the LSPRs sensitivity of Au@Cu2-xS nanoparticles with a more sharp shape perpendicular to the direction of polarization is lower.But the Au@Cu2-xS nanoparticles with more sharp cross-section shape along the polarization direction is higher LSPRs sensing sensitivity.