Study On Giant Extrinsic Chiral Metal Nanocrecents

Chirality is a general property in nature,which has an extremely wide application prospect in biology,chemistry,medicine,physics and so on.An important manifestation form of chiral structure is optical activity.The earliest discovery is the chiral molecular structure,whose optical activity occurs in ultraviolet range and weak.With the development the nanocrescent structures,the hybrid of achiral plasmonic nanoparticles and chiral molecules,chiral metal structures and chiral metamaterials are developed.Due to the limitations of these chiral structures in the preparation process,extrinsic chiral structures gradually enter into the people's field of vision.The extrinsic chiral structures is achiral,but they show the chiral effect under certain conditions.The extrinsic chiral structures are mostly two-dimensional materials,whose manufacturing process is relatively simple.Thus,these structures have found enormous applications in chiral catalysis,chiral discrimination,polarization-sensitive optical devices,broadband circular polarizers,and three-dimensional display.On the other hand,metal extrinsic chiral structures possess the plasma resonance effect,which is relatively sensitive to the size of the structure and the surrounding refractive index.All of these provide new opportunities for the application of chiral metal nanostructures.Recently,most extrinsic chiral structures were fabricated using electron beam lithography or focused ion beam,which are very expensive and time-consuming to producing the large-area extrinsic chiral structures.The extrinsic chiral structures have great potential in chiral applications.Thus,the main contents and the prominent innovations of this paper are as follows:1?The extrinsic chiral effect of the metal nanocrescent structures was investigated by numerical simulation.The optical properties of the structures are analyzed by the finite-difference time-domain method.Our results show that the metal nanocrescent exhibits giant and tunable circular dichroism effect.And the optical characteristics of the metal nanocrescent structures with different sizes and tilt angles of ion beam sputtering coating are analyzed,which shows that the resonance frequency is easily tunable.2?The large-area and monodisperse metal nanocrescent structures have been prepared and measurement the optical activity.A set of experimental system with incident wavelength of 600-2000 nm has been set up to test the circular dichroism the sample.The large-area of metal nanocrescent structures was prepared by low-cost nanosphere lithography technique.The influence parameters in the experiment are: the concentration of PS spheres solution,rotating speed,etching time,etching power,tilt angle of coating,size of PS spheres and so on.By scanning electron microscope,the shape,size and orientation of the sample are uniform.And the metal nanocrescent structures show the strong extrinsic chiral effect.The experimental results are approximately consistent with the simulation ones.3?The physical mechanism of the extrinsic chiral metal nanocrescent structures is analyzed clearly.By the simulations and experiments,we give a qualitative explanation for the giant extrinsic chirality of the metal nanocrescent,that at a non-zero incident angle ?,the excitation efficiencies of LSPR modes for the two kinds of circularly polarized light are different.From the structure of the paper,the text is divided into five chapters.The first chapter is the introduction.We start from the generation and the application of chirality,then we describe the difficulties of chiral structure in manufacturing process.Based on that,the relative advantages of extrinsic chiral metal structure are proposed.After that,we came up with our solution and discussed the strong extrinsic chirality of metal nanocrescent structure.The second chapter describes the researches on optical properties of the metal nanocrescent structure by finite-difference time-domain method.And analyzing the tunable of the resonant frequency of the different sizes of metal nanocrescents.The third chapter introduces the production process of the metal nanocrescent structures.The large-area metal nanocrescents was prepared by adjusting the parameters of different parameters.The fourth chapter introduces the construction of the experimental system and measure the spectra of the metal nanocrescent.The experimental results show that the metal crescent structure has a giant extrinsic chirality and is compared with the simulation results.Subsequently,the physical mechanism of extrinsic chirality of metal nanocrescents is introduced.The fifth chapter is the summary and prospect,summarizing this article and pointing out the next research ideas...