Boundary Integral Equation Method for the Analysis of Tunable Light Scattering Properties of Plasmonic Core-Shell Nanoparticles

The optical properties of plasmonic nanoparticles along with the plasmon resonance wavelengths are tunable by varying their size, shape and material composition. In this work we report a new efficient numerical calculation algorithm to study the light scattering properties of plasmonic nanoparticles over a wide range of wavelengths which is based on the spectral Boundary Integral Equation method. Its performances are compared with those of the Multiple Multipole Program. Plasmon resonances of gold nanostars and their wavelength dependence on the nanoparticle shape are investigated. For isolated core/shell nanostructure the dependence of plasmon resonances on the material composition is studied. Our numerical results demonstrate that the plasmon resonance of a 100 nm gold nanostar near 555 nm may be red-shifted to 593-693 nm by embedding a silica core and blue-shifted to 527-534 nm by embedding a silver core. For bimetal nanoparticles with variable core size the difference in optical response is significant only for the excitation wavelengths shorter than 580 nm, namely when the imaginary parts of the dielectric functions for both metals are significantly different. The numerical analysis demonstrates that such core shell structures are promising for biological sensing and imaging and for molecular diagnostics via plasmon resonance scattering from core/shell nanorods.