Optical response and fabrication of regular arrays of ultrasmall gold particles

We produced two-dimensinal square arrays of small gold particles by electron beam lithography. Particles with diameters of 15-35 nm and center-to-center spacings of 50 nm were fabricated over areas of 15 microm × 15microm. The optical properties were measured in the wavelength range 400-800 nm, and the results were interpreted using electromagnetic theory, including image dipole effects and the retarded dipole-dipole interactions between particles. The wavelength and width of the localized plasma absorption peak were in good agreement with the theory, provided that the interaction between the particles and the substrate was properly taken into account.