Investigation Of Optical Parameters Of Noble Metal Nanofilm Using First Principle Calculation And SPR Sensor

As the materials of various surface optical effects,noble metal films are widely applied in biological sensing and nano photonic devices,whose permittivity is a significant parameter to characterize the optical properties.Drude and Lorentz-Drude(L-D)models were the most popular models for describing the permittivity of noble metals,since their advent in the beginning of the last century.However,the electron motion described by Drude and L-D models is too idealized,which leads to the fact that the theoretical permittivity of the most frequently-used visible and near infrared band calculated by these two models is seriously deviated from the measured one and cannot be used.Moreover,the permittivity of the noble metal films varies with the thickness within 10 nm is poorly studied.Therefore,this paper tries to thoroughly investigate the permittivity and its change with thickness of Ag and Au films by simulations and experiments.The main work and new ideas include:The first principle modelings and simulations of noble metal films' permittivity.In this paper,the models of Ag,Au films are built,along with geometric optimization is run to stabilize them,then the self-consistent calculations are performed to calculate the permittivity of the noble metal films varies with the thickness within 10 nm.The calculation results show that: The real part permittivity of Ag,Au films consists well with measured one;With the thickness of Ag film increases,the simulated real part of permittivity first increases then decreases;The imaginary part of permittivity gradually decreases in the near infrared band;In the near infrared band,the imaginary part of the permittivity is gradually approaching to the measured one with the thickness increases,while there appears broadening phenomenon in the ultraviolet band.The results of the first principle simulation also show that the plasma frequency,the electron transition and the electron oscillation frequency have a significant influence on the permittivity of the films during the forming process.The determinations of Ag,Au permittivity based on angle and wavelength modulated surface plasmon resonance(SPR).Because the difference between the permittivity and its theoretical value in the visible near infrared band is the largest,and the SPR effect is not obvious outside 500~900 nm,the wavelength range adopted in the experiments is 500~900 nm.The experiment results show that the real part of permittivity determined by SPR fits well with simulated and referenced one,so as the imaginary part permittivity of Ag films measured with SPR;Because of electron transition,the thickness has an important influence on the imaginary part permittivity of noble metal films with thickness of several nanometers,and the classical models are no longer applicable.