Characterization and optical properties of arrays of small gold particles

Square arrays of 20–35-nm-diam gold particles with 50-nm spacings were formed on thick sapphire substrates by electron beam lithography. After annealing at 125 °C the particles had an approximately circular projection on the substrate with a slightly smaller dimension in the perpendicular direction as inferred from scanning electron microscopy. Optical transmission measurements were made on 15-μm square areas of particles using an optical microscope modified for microspectroscopy. The regular geometry of the well characterized samples makes possible a detailed comparison to theory.