Research On Localized Electromagnetic Enhancement Of Metallic Nano-Tip By Numerical Simulation

Under the polarization of outer electric field, a localized field will be formed with higher spatial resolution, good ratio of signal to noise and giant field enhancement factor, so it has been applied extensively in scan near-field image and surface-enhanced Raman scattering with its specific advantage and key applied value. In recent years, with the advancing of the near-field theory more deeply and perfectly to combine with the progress in nano-machining technology, which directly leads to the possible level of site-specific spectroscopy of single molecular in nanoscale. And meanwhile, due to the super character of single molecular spectroscopy to compare with the mixed spectroscopy of large moleculars, it will be produce profound meaning and important effect in fields such as biology,medicine,material and so on.The thesis investigates from the angle of possible site-specific spectroscopy of single molecular detection(SMD), a brief information of SMD techniques and the detailed applied SERS in SMD are introduced. To combine with our present researched subjects:Firstly, The model of opposing BI-Au cone- tips is established for electric field enhancement.Then, the factors that will influence the electric field enhancement are analysised using a frequency-domain Finite Element Method (FEM) by the numbers, including:(1) The optical character of metal in optical frequency-band is firstly investigated, here we mainly focus our eyes on the dispersive and absorption character of metal.(2) The parameters, that affect the electric field enhancement such as tip lengtlu the relative position between the opposing tips as well as the different tested mediums, are investigated through numerical simulation. The reasons for enhancement are explained according to the optical antenna effect and surface plasmon resonance.(3) Under the illuminated wave with 632.8nm wave-length, the influence of tip radius scale on electric field enhancement is studied. The results demonstrate that the resonance not only appearance along the polarized direction of incoming wave with the changing tip length, but also existing in vertical direction of the polarized direction, when the scale of tip radius is changing.