Study On Electron Emission Characteristics And Mechanism Of Nanostructures With Plasmon-Enhanced Effect

Recently,the photocathode for high-brightness electron source mostly uses alkali metals?including multi-alkali alloys?with low work function or III-V compounds with negative electron affinity?NEA?.Compared with the traditional photocathodes and their relatively simple morphologies,plasmonic nanostructures or materials are expected to control the incident light and manipulate the photoelectron emission.The surface plasmon resonance?SPR?is with the properties including enhanced photon absorption,enhanced localized electric field and enhanced energy transfer et al.The enhancement would improve the electron emission of the proposed plasmonic electron sources in this thesis.Plasmonic nanomaterials or structures were introduced as the photoelectron emitters,which included the periodic Au nanostructures,the large-area distribution Au nanoparticles covered with the cesium film and the carbon nanotubes decorated with Au nanoparticles.With the light-modulated scanning tunneling microscope and the electron gun and beam measuring instrument of terahertz free electron laser,the photoelectron emission characteristics were measured.The theoretical mechanism for electron emission and plasmon enhancement were discussed in detail.?1?The SPR of the proposed periodic Au nanostructures was excited at 800 nm or 532 nm,which was just the wavelength of laser applied in the research.ITO glass with low surface roughness and refractive index was adopted as the substrate.Au nanorods and Au nanotriangles were prepared by electron-beam lithography.Au nanoholes and Au nanogratings were fabricated by focusing-ion-beam etching.The reflection and transmission spectra of the nanostructures mentioned above are in agreement with the simulation for them.?2?With the light-modulated scanning tunneling microscope,the plasmon-enhanced photoelectron tunneling was found at atmosphere.the large-area distribution Au nanoparticles were prepared by the rapid thermal annealing of Au film.Femtosecond pulsed laser?⁸00 nm?was used as the excitation and introduced to the surface of the samples in a high vacuum level chamber.The maximum quantum efficiency of electron emission was observed when the SPR wavelength of nanostructures matched with the incident light.?3?Photo-injector loading experiment was performed using an electron gun and beam measuring instrument of terahertz free electron laser in CAEP.Large-area distribution Au nanoparticles covered with the cesium film were used as the emitters,and the optical excitation was the picosecond pulsed laser?⁵32 nm?.The electron emission quantum efficiency reaches10^-510^-4.The thermal emittance measured is about 1.89 mm·mrad,which can be accepted in free electron laser.?4?Vertically aligned carbon nanotubes decorated with gold nanoparticles were prepared.Under irradiation of 800 nm femtosecond pulsed laser,the modification of Au nanoparticles can significantly enhance the photoelectron emission ability.SPR of the nanoparticles was designed to be excited near the wavelength of the incident light,the maximum quantum efficiency(¹0^-5)was observed.In summary,this thesis explores the applications of plasmonic nanostructures or materials in photoelectron emission instruments.The plasmon-enhanced photoelectron tunneling emission was observed at atmosphere condition.The photo-injector loading experiment of electron-beam was initially implemented.These research work could provide the potential pathway for the novel nanostructural photocathodes with high-stability and high-efficiency.