Electromagnetic near-field nanoantennas for subdiffraction-limited surface plasmon-enhanced light microscopy

We investigate electromagnetically amplified local fields or hot spots created by surface nanoantennas for subdiffraction-limited plasmon-enhanced microscopy under total internal reflection at angled light incidence. Different shapes of near-field hot spots were calculated by varying geometrical parameters of nanoantenna structures. An inverse relationship between full-width-at-half- maximum (FWHM) and ellipticity of a hot spot was found. Among the three patterns considered, square nanoantenna patterns provided the smallest FWHM ellipticity product with a spot size of approximately 53 $\times$ 110 nm$2$ due to efficient plasmon localization. The size of a nanopattern affects FWHM significantly by producing a smaller hot spot if the size decreases. The effects of other parameters are also discussed.