Extinction And Scattering Characteristics Of Non-spherical Nanoparticles And The Applications In Particle Sizing Measurement

Different from the bulk materials,the unique localized surface plasmon resonance properties strongly depend on the shape and size of metal nanoparticles.Due to wide extinction,scattering,absorption spectrum tunable characteristics,non-spherical metal nanoparticles are widely used in biomedicine,energy,environment and other fields.Compared with the extinction spectra of non-spherical nanoparticles,the scattering spectrum contains more physical characteristics rich information of the incident light and polarization properties,which not only provide theoretical support in application of scattering characteristics of nanoparticles,but also provide the optimization objective function for particles size measurement.In this paper,the open source T matrix code is provided by NASA,and we have added the calculation function of differential scattering cross section,polarization degree and scattering intensity.Scattering and polarization properties of scattered light of non-spherical gold nanoparticles are theoretically simulated.The results show that when the particle orientation is random,the degree of polarization changes with the scattering angle in sine function,and depends strongly on the particle size and shape.What's more,the corresponding characteristics of extinction,scattering spectrum and particle size are theoretically analyzed.The dependence of spectrum and size is different,which provides theoretical guidance and data support for the measurement of non-spherical nanoparticle size.The size and concentration of metal nanoparticles affect their optical properties,and determine their behavior in practical applications.At present,the research on the particle sizing of noble metal nanoparticles based on spectral extinction method has achieved positive results.But for non-spherical metal nanoparticles,particle size measurements include two-dimensional size distribution and concentration distribution,thus the inversion algorithm and accuracy need to be improved.It is found that it can be expected to develop in the measurement of particle size distribution of non-spherical particles with more scattering,extinction and polarization information.In this paper,based on the extinction and scattering properties of particles,the size inversion problem of monodisperse and polydisperse gold nanorods are analyzed theoretically,and the influence of noise on the inversion results is studied quantitatively.The results show that both the particle size distribution and spectral inversion results agree well with the original data with different noise conditions,so the inversion algorithm is stable and reliable.In addition,the extinction spectra and angular scattering spectra of gold nanorods in different sizes are measured,and the evaluation function of inversion initial value is established.The size and concentration errors of the sample particle system are all less than 10% using the spectral extinction/scattering method combining with the constrained regularized least square algorithm.The results are in good agreement with the nominal values,the feasibility of the measurement method is preliminarily verified.There are more spectral information using the spectral extinction/scattering method,and it can effectively improve the accuracy of the inversion of particle sizing of non-spherical particle system,which is expected to provide a non-spherical particle size distribution measurement system.However,more accurate and reliable experimental measurements and multi-objective optimization algorithms need to be further studied.