Measurement And Investigation Of Dielectric Constants Of Noble Metal Nanofilm Based On SPR

The noble metal nanofilm has different optical properties from the bulk material and is related to the film thickness,and is the structural basis of the nano photoelectric sensor and the photonic device.In order to accurately predict the performance of a photonic device,it is necessary to grasp the optical characteristic parameters of the precious noble metal nano film,that is,the dispersion characteristic and thickness dependence of the dielectric constant.However,the classical Drude model or Lorentz-Drude(L-D)model used to describe the dielectric constant of noble metals does not match the experimental data in the visible-near-infrared spectral region.The commonly used transmission-reflection method introduces a large dielectric constant imaginary error when measuring the dielectric constant.In view of the above problems,this paper is based on the surface plasma resonance(SPR)effect of the near-infrared spectral region with extremely high sensitivity.Theoretical analysis and experimental measurement of the dispersion characteristics of the dielectric constant of noble metal nanofilm;in order to further explore the influence of the thickness of the noble metal nanofilm by the thickness of the film,the relationship between the dielectric constant and the thickness of the multi-thickness film was measured by ellipsometry.The main work and innovations of this thesis include:Based on the principle of wave vector matching for exciting SPR,a sensing model of dielectric constant and nano film thickness is established.The simulation of the variable parameters such as wavelength,film thickness and prism material in the measurement performance of SPR film is carried out,and the influence of each variable on the measurement performance of SPR is discussed.Finally,the simulation analyzes the range of film thickness with high sensitivity response in phase modulation.The sensing model and parameter simulation provide a theoretical basis for the measurement of the dielectric constant and thickness of noble metal nanofilms,making the uncertainty of the film thickness range in the experiment more accurate.An accurate measurement of the dielectric constant of a noble metal film based on the SPR theory in the visible-near-infrared region.Firstly,in order to ensure the consistency of the sample,a standard magnetron sputtering method was established to prepare a noble metal nanofilm,and a multi-thick noble metal nanofilm was prepared.The angular modulation SPR system was built using key instruments such as supercontinuum source and high-precision electric rotary stage.The dielectric constants of gold and silver films with thicknesses of 35 nm,45 nm and 55 nm were measured.The measurement result of the ellipsometer is used as a reference value.The comparison of the results of different methods shows that the dielectric constant of the gold film and the silver film in the visible-near-infrared region obtained by SPR measurement greatly reduces the data error of the imaginary part,and the result is more accurate.The dielectric constant measurement experiments of multi-thick noble metal nanofilms were carried out using SPR system and ellipsometer.Combined with the electron relaxation time theory of noble metal films,the tendency of the dielectric constant of the film to change with thickness is predicted,that is,the real and imaginary parts of the dielectric constant will increase with decreasing thickness.The experimental results of the dielectric constant of the ultra-thin noble metal film of 5~55nm prove the correctness of the prediction trend.The results also show that in the optical constant of the film,the refractive index increases with the decrease of the thickness,but the extinction coefficient decreases with the decrease of the thickness.