Optimization of growth and ordering of Ag nanoparticle arrays on ripple patterned alumina surfaces for strong plasmonic coupling.

Low-energy ion beam sputtering of alumina thin films followed by growth of metallic nanoparticles by glancing angle deposition is optimized in order to produce arrays of silver nanoparticle chains with a strong plasmonic dichroism. A systematic study is undertaken in order to establish the influence of the angle of silver deposition and the ordering of the pre-patterned rippled surface on the morphology and organization of the nanoparticles, and on their associated optical properties. High ion fluence for ripple formation and low glancing angle for metal deposition favor the formation of aligned and elongated particles with sub-nanometer gaps. Numerical simulations show that these nanoparticle arrays generate high electric field enhancements for an excitation parallel to the particle chains, and therefore can be used for surface enhanced spectroscopies.