Field Enhancement around Metal Nanoparticles and Nanoshells: A Systematic Investigation

Metal nanoparticles and nanoshells consisting of metal shells and dielectric cores are known to significantly enhance incident electromagnetic fields around themselves due to surface plasmons. The field enhancement factors were calculated for spherical metal nanoparticles and nanoshells in the quasistatic limit using empirical wavelength-dependent dielectric constants. Dependence of the field enhancement factor on various parameters, such as wavelength, distance from the nanoparticle/nanoshell, metal element, dielectric core material, surrounding medium, and diameter ratio between the core and the shell, was investigated. Interestingly the peak field enhancement factor becomes largest with core-to-shell diameter ratio at ∼0.9 for any combination of noble metal shell and dielectric core. As a consequence of the parameter optimization, it was found that an Ag nanoshell with a Teflon core with a core/shell diameter ratio of 0.88 exhibits a peak field enhancement factor of 1400 in its vicinity in water.