Metal nanoparticle size effect on local near-field enhancement

We have used numerical calculations based on Mie theory to analyze the near field distribution patterns for 4-150 nm spherical silver nanoparticles (nanospheres). We have shown that as the nanoparticle sizes increase, the region where 'hot spots' are concentrated is shifted to the forward hemisphere. We have observed a nonmonotonic dependence of the maximum attainable local field enhancement factor on the size of the silver nanospheres. We have determined a correlation between the optimal nanosphere size for the maximum attainable local field enhancement factor and the optical absorption efficiency factor. We have established a nonmonotonic dependence of the optimal size of the nanoparticles and the maximum attainable local field enhancement factor on the refractive index of the surrounding medium. (authors)