Research On The Abnormal Light Transmission Characteristics And Optical Chirality Of Metal Micro-nano Structures

When a light excites on the surface of metal micro-nano structure,on metal surface free electrons couple with photons,which forms a near field electromagnetic wave that propagates along metal surface.We called this electromagnetic wave as Surface plasmon(Surface Plasmon,SP).Surface plasmon can be divided as non-propagated localized surface plasmon(LSP)and propagated surface plasmon polariton(SPP).Metal micro-nano structure based on these characteristics of LSP and SPP have been widely focused by researchers,and been applied in different fields,including molecular sensors,photonic chip,solar cell,optical storage,and so on.By the finite element method(FEM),molecular self-assembly,and glancing angle deposition,the thesis designs micro-nano hole array to study transmission characteristics,fabricates chiral micro-nano structures to study different coupling mechanisms of CD,introduces graphene micro-nano structures to induce molecular CD signal from ultraviolet region to microwave region.The main research works of this thesis are listed as follows:1.The thesis designs X-shaped plasmonic nanohole arrays,and studies its EOT characteristic.Numerical results show that obvious peaks appear in the transmission spectra.By analyzing electric field distribution,we found that these peaks are due to LSP resonance of nanohole,SPP resonance on the top surface of the silver film,and Fabry-Ferot resonance in nanohole.Besides the topologic shape parameters of the X-shaped nanohole,transmission properties strongly depend on incident polarization.The results of this study not only present a tunable plasmonic filter,but also aid in the understanding of resonant EOT phenomenon.2.The thesis designs diamond-shaped nanohole arrays,and studies its EOT characteristic.Numerical results show that when light excites on the diamond-shaped nanohole arrays,on two sides of its forms non-resonant electromagnetic coupling,and then achieves broadband transmission and enhancing local electric field.EOT strength strongly depends on incident polarization and the topologic shape parameters of the diamond-shaped nanohole.The results of this study not only present a broadband plasmonic filter,but also aid in the understanding of non-resonant EOT phenomenon.3.Applying the technology of glancing angle deposition(GLAD),a concise method is proposed to fabricate metal chiral nanostructures.L-shaped Ag nanostructures(LSANs)composed of two slices with different thickness is stacked on self-assembled monolayer polystyrene nanosphere arrays by controlling substrate azimuth and deposition time.Experimental results show that the strong optical chirality of LSANs is achieved in visible and near-IR regions by measurement.For the circular dichroism spectrum of LSANs,the intensity is enlarged,and its peaks red-shift with increasing thickness difference.When LSANs are stacked on polystyrene spheres of different diameters,enlargement and red-shift are also observed in their circular dichroism spectra with increasing thickness difference.The numerical calculations of finite element method show that the two slices composing LSAN provide cross-electric dipoles and their thickness difference provides phase difference for generating optical chirality.This study not only provides a concise method to fabricate metal chiral nanostructures,but also contributes to understand the knowledge of the mechanism of circular dichroism.4.The thesis theoretically analyzes the transmission matrix T and proposed the chiral plasmonic nanostructure of twist nanoslit-nanorod arrays(TNNAs)in this study.Numerical results show that,at around resonant wavelengths,the spectra of T++ and T__correspondingly present peaks and valleys leading to a large CD effect.Meanwhile one of the spectra for Th_+ and T+-presents valleys and another presents peaks leading to a large AT effect.More importantly,at around resonant wavelengths,the magnitude of CD is equivalent to that of AT.In addition,the CD and AT effects strongly depend on the geometric parameters of TNNAs.These results are useful for designing negative refractive index media and perfect polarization converters.5.The thesis proposes a nanosystem of twist nanorods separated by a metal film(TNMF).Numerical results show that a new indirect coupling mechanism is found in the CD spectrum of TNMF,except original direct coupling.According to the equivalent LC resonant circuits,gold nanorods on the two sides of the gold film can be regarded as a receiver and an emitter.By monotonously varying geometric dimensions,the strength of direct coupling mode can be tuned monotonously,which cannot be explained by impedance matching;the strength of indirect coupling mode can be tuned to its maximum,which can be explained by impedance matching.These results can help design novel chiral optical structures and propose an indirect coupling mechanism for generating CD signal.6.The thesis demonstrates theoretically that plasmon-induced CD is approximately contributed by the crossinteraction between equivalent electric and magnetic dipole moments for chiral molecules and Plasmon nanostructures,and proposes a more reliable damping coefficient of electromagnetism.To prove electromagnetic couplings,we introduce graphene into plasmon nanostructures and design asymmetrically inscribed graphene dual-rings arrays(IGDAs)with high-order hybrid modes.Numerical results show that ultrahigh-order resonances of IGDAs induce molecular CD signals from ultraviolet region to microwave region.The maximum enhancement factor of induced CD could reach up to four orders of magnitude.Mature microwave technology more easily detect this induced CD signal.In addition,an induced CD signal could be tuned only by varying the Fermi energy of IGDAs rather than by remading IGDAs.These results can help design dynamical chiral sensors in bioinstrumentation and chemical analysis.