| Metal nanoparticles and metal-based composite nanostructures applied in optical sensing and testing technology possess abundant localized surface plasmon resonance(LSPR)properties,which have great potential in petroleum exploration and development.The LSPR properties of metal-based composite nanostructures have attracted extensive attention due to its resonance spectrum controllability and functional diversification.In order to design new LSPR composite nanostructures and provide the theoretical basis for “Oil and gas optics” and sensing measurement method,optical properties of gold-based composite nanostructures are investigated systematically by the simulation method based on the principle of LSPR.The extinction properties of Au-interlayer-Ag multilayer nanoshells with different kinds of interlayer materials are simulated and analyzed.The influence of interlayer material,core-shell ratio and refractive index of the surrounding medium on the extinction efficiency and LSPR wavelength of multilayer nanoshells are studied by the discrete dipole approximation(DDA).The numerical results indicate that the coupled resonance mode wavelengths show a remarkable dependence on the Au core radius,refractive index of the surrounding medium,and different kinds of interlayer materials.In the spectrum of Au-interlayer-Ag multilayered nanostructures,different interlayer materials show a remarkable influence on the LSPR properties of multilayered nanoshells.There are three resonance peaks exist in the spectrum when the interlayer is cavity and the fano resonance phenomenon exists in the spectrum of Au-cavity-Ag nanoshells.A metallic Ni interlayer suppresses the contribution of the Au core to LSPR and only the Ag-dominating peak is observed from the extinction spectra.and no fano resonance is formed.The interlayer Si3N4 can enhance the contribution of LSPR and three resonance peaks exist in the spectrum.By selecting the suitable geometric parameters,the fano resonance peaks of Au-interlayer-Ag multilayer nanoshells can be tuned between 600 and 1200 nm.A new kind of symmetry-breaking Au-ITO-Ag multilayer nanoshells is proposed,and the influence of polarization direction and frequency of incident light on the LSPR energy modes and far-field distribution are studied further by finite element method(FEM).The study found that the energy level distribution of plasmon resonance hybridization in the Au-ITO-Ag symmetry breaking is sensitively dependent on the polarization of the incident light.When the polarization of the incident light is perpendicular and parallel to the axis of symmetry,multiple dipolar and high order plasmon resonance peaks can be excited because of the interaction between energy mode of Au core and Ag nanocup.The independent control of the LSPR spectra of transverse coupling and axial coupling is realized when the frequency of the incident light changes in the certain range.Comparing with the absorption spectrumand scattering spectrum,the energy modes of scattering spectrum are blue-shifted and the absorption efficiency is greater than the scattering efficiency.The absorption efficiency play a dominate role in the extinction property of surface plasmon resonance.The analyzed electric enhancement contour indicates that the gap part of Ag outer nanocup has the most prominent electric field intensity and highly adjustable optical properties.Silver nanorod arrays(SNRs)deposited on a graphene-coated Au substrate nanostructure is designed and the effects of the axial direction of Ag nanorods,graphene layer thickness,Ag nanorod arrays height,resonance peaks and refractive index of the surrounding medium on the LSPR properties of the hybrid nanostructure are investigated by the discrete dipole approximation method.The electric field enhancement contour around the Ag nanorod arrays/graphene/Au structure is analyzed based on multiple resonance modes.Numerical simulation reveals that when the axial direction of Ag nanorods is parallel to the y axis,three types of plasmonic modes with different resonance characteristics are localized on the SNRs/graphene/Au nanostructure.The LSPR modes show a blue-shift by increasing the thickness of the graphene layer in the metal nanoparticle(NP)-graphene hybrid nanostructure.The thickness of graphene layer has a significant effect on the LSPR properties,and the resonance characteristics of composite nanostructure can be adjusted and optimized by controlling the thickness of graphene.The resonance peak corresponding to the LSPR energy mode varies with the height of the Ag nanorods,and bears a close relationship with the aspect ratio of the Ag nanorods.In the hybrid nanostructure,the contours of the electric field enhancement of the silver nanorods at different resonance wavelengths present different response characteristics.The study also found that,in the nanostructure of graphene-coated Au substrate decorated with eight silver nanorod arrays,the stronger electric intensity is 70 times more than the electric field of incident light at 800 nm.The localized electromagnetic field interaction between Ag nanorods leads to the strong Raman signal,which can be used to amplify and detect the near-field signal.The slight change of refractive index of the surrounding medium results in the change of the LSPR resonance condition of the Ag nanorod arrays/graphene/Au structure.The response relationship provides theoretical basis into metal NP-graphene hybrid nanostructures which have potential applications in preparing higher SERS active substrate refractive index sensors.The LSPR optical properties of gold-based composite nanostructure are investigated systematically,which reveals the relationship between structural parameters and extinction efficiency and LSPR resonance wavelength.A new kind of symmetry-breaking Au-ITO-Ag multilayer nanoshells with high adjustable optical properties is proposed and a novel silver nanorod arrays deposited on a graphene-coated Au substrate nanostructure is designed.The research results have theoretical guidance and practical significance for the surface functional modification of optical fiber sensor and the design of composite nanostructure optical sensor. |
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