Study On Plasmonic Enhancement And Nonlinearity Of Metal Nanoparticles By Surface Integral Equation Method

With the rapid development of micro-nano manufacturing process,the design of electromagnetic(EM)devices tends to be miniaturized and short-wavelength.The research and design of nano-sized components has attracted more and more researchers' attention.The metal nanoparticles(NPs)are widely used for the fields of integral optics,solar cells,super-resolution imaging,biosensing,etc,since they can generate localized surface plasmon resonance under the excitation of EM waves,and support the local field enhancement,thereby greatly improving the nonlinear response of the surrounding medium.Metal NPs have lost good conductor property in the optical band,which are characterized by media.The unique local field enhancement and nonlinear effects have prompted people to carry out theoretical and numerical studies on the interaction between EM fields and nanomaterials.Based on the classical EM theory,we numerically simulate the EM scattering of the medium,the plasmon-enhanced thin-film solar cells,and the nonlinear second harmonic response with surface integral equation(SIE)method.The first part of this dissertation studies the basic theory of computational electromagnetics(CEM).For the macro EM field problem,the Maxwell's equations,constitutive relations of media,boundary conditions and Helmholtz theorem are introduced.Specific to the EM scattering problem,method of moments(Mo M),fast multipole algorithm(FMA)and radar cross section(RCS)are introduced.This part provides a theoretical basis for the numerical analysis of the interaction between electromagnetic waves and metal nanoparticles.The second part of this dissertation studies the efficient SIE method for EM scattering problem.Firstly,we derive the solution of SIE for the EM scattering problem of uniform medium with method of moments(Mo M)and numerical iteration of generalized minimal residual(GMRES).Secondly,in order to improve the computational performance and computational power,the fast multipole algorithm is applied to the SIE method with complexity analysis.Finally,in order to improve the convergence of SIE,a novel mixed inner-outer iterative technique is proposed to improve the computational efficiency of the SIE method with high accuracy.In addition,the proposed method is perfectly compatible with sparse approximate inverse precondition.This part provides a numerical tool for simulation of the plasmon enhancement and nonlinear effect of metal NPs.The third part of this dissertation studies the plasmonic enhancement of metal NPs by SIE method.Firstly,the SIE method is used to analyze the local surface plasmon of metal NPs with field enhancement factor.Secondly,a semi-classical quantum mechanic/electromagnetic(QM/EM)method is proposed for efficient simulation of plasmon-enhanced thin-film cells.In this method,the local EM field enhancement is introduced into the electron-photon coupling by second quantization,and the nonlinear photovoltaic process is sovled by density functional tight binding(DFTB)theory combined with non-equilibrium green function(NEGF),which provides a comprehensive understanding from atom level.Finally,the proposed QM/EM method is applied to study the influence of spherical metal NP materials,quantity,position distribution and drop-casting ratio on the photovoltaic performance of thin film batteries.The proposed method starts from atomic scale modeling and deeply understands the nonlinear photovoltaic process,which provides theoretical support for the industrial manufacture of plasma-enhanced thin-film cells.The fourth part of this dissertation studies the nonlinearity of metal NPs by SIE method.Firstly,the relationship between the surface plasmon phenomenon of metal nanoparticles and the nonlinear effect is discussed.The second-order nonlinear process and its numerical modeling method are analyzed.Secondly,for the nonlinear second harmonic(SH)generation of arbitrary shape metal nanoparticles,an efficient SIE method is proposed with the mutual coupling between the fundamental field and the SH field into consideration.Finally,the SIE method is applied to the character study of the SH from metal NPs,including radiation directionality,interface sensitivity and enhancement methods.In conclusion,based on the surface integral equation,numerical methods for analyzing the plasmon enhancement and nonlinear second harmonic of metal nanoparticles are proposed.Numerical examples are demonstrated to show the accuracy,stability and efficiency of each method.