Numerical Investigation Of Refractive-index Sensitivities Of Noble Metal Nanoparticles' Localized Surface Plasmon Resonance

Noble metal nanoparticles have important applications in optical sensing and detection due to their unique localized surface plasmon resonance(LSPR)properties,which are widely tunable by nanoparticles' morphology,size,material,and surrounding medium.The investigation of their LSPR tunability is one of the hot topics in nano photonics.Additionally,there are still no reports devoted to uncover the generalized parameter controlling the refractive index sensitivities of diverse noble metal nanoparticles.In this thesis,we numerically investigated LSPR sensitivities of individual gold nanorods with different cross-section shapes,two types of ellipsoidal nanoparticles,and nanothick-dielectric-encapsulated Ag nanosphere multimers by discrete dipole approximation(DDA)method.The underlying factors affecting their LSPR sensitivities are analyzed and the controlling way are summarized as well.The main contents of this thesis are as follows.1.By calculating the far-field scattering spectra of individual gold nanorods with different cross-section shapes(triangle,square,pentagon,hexagon,and circle),the aspect ratio and cross-section shape dependent refractive index sensitivity(S,Refractive Index Sensitivity)and quality factor(FOM,Figure of Merit)of individual gold nanorods are investigated.The results show that the cross-section shape of gold nanorods can tune S and FOM,but does not change the overall response characters of S and FOM to.The optimal FOM is predicted to locate at aspect ratio ?3 for all concerned gold nanorods.It also demonstrates that to better compare with simulation results,for different optical bands,different fitting models(to the real part of the dielectric function of the metal)are more appropriate to describe their responses of S and FOM to.2.By calculating the far-field extinction spectra of Au ellipsoidal-like nanoparticles(nanorods and nanodisks),the general parameter controlling S and FOM of individual Au nanoparticles is discussed.The results show that for the concerned rod-shaped and disk-shaped nanoparticles,their S responses to aspect ratio linearly with two different slope,while the optimal FOM is achieved at optimal different aspect ratio of 3(nanorods)and 8(nanodisks).Employing spheroidal theory,it reveals that for both two types' concerned nanoparticles,their S responses to their shape factors quadratically and that they gets optimal FOM at the same shape factor ?10.5.The shape factor is demonstrated to provide the general parameter determining their S and FOM.The obtained results provide an effective way to indirectly predict the optimal FOM through the corresponding shape factor.3.By calculating the far-field absorption spectra of nano-thick-dielectric encapsulated Ag plane-nanosphere multimers,the effect of thick dielectric encapsulating on the corresponding refractive index sensitivities are discussed.It shows that the dielectric encapsulation does not destroy the quadratic response of Ag plane-nanosphere multimers to the refractive index of the surrounding medium.Yet,it weakens the quadratic magnitude of such response to some degree,which can be well explained in terms of Rayleigh approximation and core-shell nanoparticle model.Compared to naked case,nano-thick-dielectric encapsulation is revealed to not diminish the optical refractive index sensing capability of encapsulated Ag plane-nanosphere multimers.The obtained results herein are significant not only from fundamental point of view,but also crucial to provide important data for future devices of LSPR based sensing and detection.