The Study On The Optical Trapping Manipulation And Surface Enhanced Raman Scattering Of Metal Plasmonic Microstructures

The rich optical properties of subwavelength metal microstructures and the corresponding excitations,couplings and propagations of surface plasmon polariton have been hot research topics of energy science,information science,material science as well as their inter-disciplines.In recent years,with the continuous theoretical research and the rapid development of precision processing and control technology of micromaterials,various design of functional novel metal plasmonic microstructures aiming at different application fields emerge frequently,which provide an effective way to manipulate the photons and tune the light matter interactions,and show great application prospect in the efficient photoelectric conversion,nonlinear optical effect enhancement,nanointegrated optical chip and other fields.This thesis focuses on the scientific issues of how to control the excitations and propagations of electromagnetic wave in medium using the metal plasmonic microstructures,by studying the the realization mechanism of efficient and broadband optical trapping manipulation and exploring the surface enhanced Raman scattering effect based on the synergy of optical absorption and enhancement of local electromagnetic field.The first part of this thesis studies experimentally and theoretically the ultra-broadband tunable resonant light absorber based on two-dimensional randomly metal microstructures.In the second part,a new kind of metal microstructure supporting the coupling of hybrid spoof surface plasmons and microcavity mode is designed in order to overcome the fatal weakness of the quantum well infrared photodetectors,which can realize the efficient optical coupling of the quantum wells in the very-long-wavelength-infrared band(14?m-16?m).In the third part,a series of large area and high uniform metal micro structure arrays were fabricated by the nanoimprint lithography,the improved nanosphere lithography as well as the deposition technology of metal nanoparticles.Their regulation and control on surface enhanced Raman scattering(SERS)is also explored.The thesis is mainly composed of three sections that are arranged as following:1.We demonstrate a simple method to create a wideband near-unity light absorber by introducing a dense and random pattern of metal-capped monodispersed dielectric microspheres onto an opaque metal film by well-developed self-assembly method.The absorber works due to the excitation of multiple optical and plasmonic resonant modes.To further expand the absorption bandwidth,two different-sized metal-capped dielectric microspheres were integrated into a densely packed monolayer on a metal back-reflector.This proposed ultra-broadband plasmonic-photonic super absorber demonstrates desirable optical trapping in dielectric region and slight dispersion over a large incident angle range.Without any effort to strictly control the spatial arrangement of the resonant elements,our absorber,which is based on a simple self-assembly process,has the critical merits of high reproducibility and scalability and represents a viable strategy for efficient energy technologies.2.Quantum well infrared photodetectors(QWIPs)have developed rapidly due to their low cost,excellent reproducibility as well as high uniformity compared with the traditional mercury cadmium telluride(MCT)infrared photodetectors.However,for n-type QWIPs,due to the inter-subband absorption selection rules,they cannot detect light at normal incidence where the electric field is parallel to the plane of quantum wells.We propose a highly efficient metallic optical incoupler for a quantum well infrared photodetectors operating in the very-long-wavelength-infrared band,which consists of an array of metal micropatches and a periodically corrugated metallic back plate sandwiching a semiconductor active layer.By exploiting the excitations of microcavity modes and hybrid spoof surface plasmons(SSPs)modes,this optical incoupler can convert infrared radiation efficiently into the quantum wells(QWs)layer of semiconductor region with large electrical field component(Ez)normal to the plane of QWs.Our further numerical simulations for optimization indicate that by tuning microcavity mode to overlap with hybrid SSPs mode in spectrum,a coupled mode is formed,which leads to 3 3-fold enhanced light absorption for QWs centered at wavelength of 14.5 ?m compared with isotropic absorption of QWs without any metallic microstructures,as well as a large value of coupling efficiency(?)of |Ez|2?6.This coupled mode shows a slight dispersion over?44° and weak polarization dependence,which is quite beneficial to the high performance infrared focal plane arrays devices(FPAs).3.We fabricated a series of large-area,high uniform metal microstructure arrays as SERS substrates by the nanoimprint lithography,the improved nanosphere lithography as well as the deposition technology of metal nanoparticles.First,we propose and demonstrate a SERS substate consisting of gold/PC nanopillars arrays,the optical properties can be easily tuned by changing the parameters of the anodic aluminum oxide(AAO)templates and the quantity of the gold deposition.The nanogaps actually build up a three-dimensional(3D)hot-spot network for high-performance SERS detection due to the near-field coupling of the localized surface plasmon.In addition,since the gold/PC nanopillars arrays were actually supported on flexible plastic PC films,physical forces such as bending and twist:ing could provide anther degree of freedom to tune the SERS properties.Secondly,a hotspot-engineered quasi-3D metallic network with controllable nanogaps is purposed as a highquality SERS substrate,which is prepared by a combination of non-close-packed colloid monolayer templating and metal physical deposition.A remarkable average SERS enhancement factor of up to 1.5×108 and a SERS intensity relative standard deviation of 10.5%are achieved by optimizing the nanogap size to sub-10 nm scale,leading to an excellent capability for Raman detection,which is represented by the clearly identified SERS signal of the Rhodamine 6G solution with a fairly low concentration of 1 nM.In addition,Ag nanodot arrays with large-area on silicon substrates were fabricated based on phase separation lithographya and they exhibited a SERS enhancement factor of up to 1.64x 108 with high uniformity.Compared with traditional fabrication methods,the phase separation lithography is an extremely simple,low-cost,and easily accessible methods for fabrication of nanostructure with wafer-scale.