Research On Near-field Plasmon Properties Of Low-dimensional Metal And Graphene Structures

Surface plasmon polarization(SPP)is an elementary excitation of the coupling mode by the excited collective oscillations of free electrons and the electromagnetic field,which is bound to the material-medium surface.Surface plasmon gets a lot of attention,because it can propagate in structures beyond light diffraction limit and enhance the localized electromagnetic field.At a certain wavelength,a laser can excite surface plasmons on materials,such as metal,graphene and so on.The metal nanostructure is a good support for surface plasmons with different modes.While graphene materials can tailor the properties of surface plasmons and have a lower propagating loss,which can be used for further optoelectronic information transmission and detection.In this dissertation,we focused both experimentally and theoretically on near-field plasmon properties of one-dimension metal nanowires and one-dimension graphene wrinkle defects.One-dimension metal nanowires can support the propagating and localized surface plasmon modes simultaneously.In an experiment,we proved the existence of near-field plasmon optical forces on metal nanowires by the movement of nanoparticles in a liquid.By analyzing the motion,the direction of nanoparticles' movement is driven by the thermal convection.Based on these,we can control the guided movement of nanoparticles by changing the nanowires' topography or the laser polarization.One-dimension graphene wrinkle defects,with small geometric sizes,can influence the propagation of graphene surface plasmons.By the near-field optical microscopy,we realized the real-space optical imaging of graphene wrinkles.Combining the experiment and simulation results,we found the reflection effect for surface plasmons is mainly caused by the optical conductivity changing of wrinkles,not the topography effects.Thus,the reflection effects can be tailored by changing the wrinkle properties.And,graphene edges and wrinkles can all induce the plasmon reflection.We can get the synergetic real-space imaging of these two factors.By comparing the experiment and simulation results,the synergetic effect is in contrast with different kinds of optical conductivity changing at wrinkles.For the increased one,the synergetic result is a constructive interference.While for the decreased one,the synergetic result is a coherent subtraction.That means,we can judge and analyze the optical and electrical properties of wrinkles by the near-field optical imaging.Generally speaking,the high tunability of surface plasmon properties in low-dimension metal or graphene structures makes them of critical importance on plasmonics.Recognizing them,we will get the key of plasmonic manipulation;use them,we will open a new door for plasmonics application.