The Electron Microscopy Technology Research Of The Local Surface Plasmon In Metal

Local surface plasmon polaritons,the coupling oscillation of external electromagnetic field and metal free electrons,has led to a variety of applications in many areas such as surface-enhanced fluorescence,surface-enhanced Raman scattering,etc.It behaves differently with different shape,size,material of the metal nanoparticles.Recent years,with the rapid development in electron microscopy technology,based on the stable technology of the optical path and electron gun,especially the use of double spherical aberration correctors,the energy resolution and spatial resolution of the scanning transmission electron microscope(STEM)has been improved significantly.Using the STEM equiped with double spherical aberration correctors,to study the local surface plasmon polaritons of Au monomer and dimer,we obtained the high angle annular dark field(HAADF)and the spectrum image(SI)of electron energy loss spectroscopy(EELS)of the Au monomer and dimer.Through the HAADF we can describe the outline of the nanoparticle.After the calibration and normalization of SI,we can extract the EELS in and around the Au nanoparticle.The local surface plasmon polaritons of Au monomer and dimer clearly show two kinds of resonance modes,dipole resonance locate at 1.5eV and quadrupole resonance locate at 2.4eV.The local surface plasmon polaritons of Au nanoparticle occurs the"red-shift" phenomenon with the electron probe moving away from it.Energy filter images according to 1.5 eV and 2.4 eV display different space pattern of the resonance modes.The attenuation distance and absorption area of local surface plasmon polaritons can be deduced through the energy filter images.The results show that the radius of the local surface plasmon polaritons absorption is about 20 nm larger than the physical size of the Au nanoparticle.In order to verify the experimental results,we calculate the low-energy electron energy loss spectrum of Au monomer and dimer using COMSOL Multiphysics software.We look into the coupling resonance case between local surface plasmon polaritons and high energy incident beam,and find that the location of the resonance absorption peak reproduces the "red-shift" phenomenon when the electron beam is away from the particle surface.This "red shift" phenomenon has nothing to do with the specific shape of particle,but the dispersion relation of surface plasmon.In conclusion,we study the local surface plasmon polaritons of Au monomer and dimer using advanced scanning transmission electron microscopy technology.We analysis the red-shift phenomenon and the absorption area of local surface plasmon polaritons through the spectrum image technology,and modeling our experiment with the COMSOL Multiphysics software,the simulation results fit well with the experimental data,which verify the results of the experiment.