Fabrication And Optical Properties Of Metal Nanostructure Arrays

Surface plasmon resonance in metallic nanostructures is the collective oscillation of the free charge induced by the incident light.Under resonant excitation,metallic nanostructures have the unique optical properties and extremely large electric field enhancements around the nanocrystals.These properties are extremely useful for applications across many different fields,such as optoelectronic circuit,biomedicine,information technology,renewable energy and metamaterials.Metallic nanostructures have the unique ability to concentrate the free-space optical field within subwavelength regions adjacent to their surfaces,which can significantly enhance the light-matter interactions and improve the optical response of the metal and the nearby material.In this paper,we prepared different metallic nanostructures array by electrochemical deposition in anodic aluminum oxide(AAO)templates,and further studied the surface plasmon optical properties.Our work mainly includes:Firstly,we report the synthesis of plasmonic arrays composed of two-segment dimer nanorods and coaxial cable nanorods with?1 nm gap insulated by a self-assembled Raman molecule monolayer.The gap-induced plasmon coupling generates an intense field in the gap region of the dimer junction and the cable interlayer.As a result,the longitudinal plasmon resonance of nanorod arrays with high tunability is obviously enhanced.Most interestingly,the field enhancement of dimer nanorod arrays can be tuned by the length ratio L1/L2 of the two segments,and the maximal enhancement appears at L1/L2 = 1.In that case,the two-photon luminescence of dimer nanorod arrays and the Raman intensity in the dimer junction is enhanced by 27 and 30 times,respectively,under resonant excitation.In the same way,the Raman intensity in the gap region is enhanced 16 times for the coaxial cable nanorod arrays.Secondly,Ag nanorod(Ag NR)arrays with average diameter about 18 nm were electrodeposited in anodic aluminum oxide templates.The filling factor of Ag NRs in the AAO nanopores could be adjusted by the deposition temperature.The filling factor increased to 98%when the deposition temperature decreased to 1?.As the filling factor increased,the plasmon absorption intensity of Ag NR arrays was greatly enhanced.Meanwhile,the AgNR:AAO exhibit strong photoluminescence at 570 nm,obviously different with that of the bare AAO at 495 nm.The photoluminescence intensity at 570 nm increased with the increase of filling factor.The underlying mechanism of photoluminescence enhancement is further investigated and discussed by using time-resolved photoluminescence techneque.Thirdly,we report plasmon-mediated cooperative emissions of approximately one monolayer of ensemble CdSe/ZnS quantum dots coupled with silver nanorod complex cavities at room temperature.Power-dependent spectral shifting,narrowing,modulation,and amplification are demonstrated by adjusting longitudinal surface plasmon resonance of silver nanorods,reflectivity and phase shift of silver nanostructured film,and mode spacing of the complex cavity.The nonlinear emission of CdSe/ZnS quantum dots can be modulated by the complex cavity.The underlying physical mechanism of the nonlinear excitation energy transfer and nonlinear emissions are further investigated and discussed by using time-resolved photoluminescence and finite-difference time-domain numerical simulations.Finally,we report the fabrication of plasmonic arrays composed of Au/Ag bimetallic nanopartic by the two-step electrochemical deposition.After the deposition of Ag,the Au nanoparticle evolved to several smaller Au/Ag bimetallic nanopartics in each hole.We investigated the catalytic and SERS activity of Au/Ag bimetallic nanoparticle arrays.They exhibit catalytic properties superior to those of the Au nanoparticle arrays.The SERS intensity of the 4-mercaptobenzoic acid(4-MBA)with the Au/Ag bimetallic nanopartic arrays is approximately 18.6 times larger than that of the Au nanoparticle arrays,and a low detection limit of 10-10 M 4-MBA can be achieved.By combining their catalytic and SERS activity,we further establish the use of the Au/Ag bimetallic nanoparticle array for in situ SERS monitoring of surface catalytic reactions.