Near-field images of surface plasmon eigenmodes in gold nanogratings

In this study, we have fabricated gold nanograting structures by using a focused-ion-beam system. The nano-optical properties were examined by using both the scattering- and transmission-mode near-field scanning optical microscope (NSOM). The surface plasmon (SP) eigenmode in this periodic nanostructure is directly observed by the scattering-mode NSOM. Two SP waves, localized fields and propagating waves, generating in the near field were found by the transmission-mode NSOM, and the dependence of wavelengths was studied. The relations of scattering- and transmission-mode results were discussed as well.