Uniform gold nanorod arrays from polyethylenimine-coated alumina templates

Monolithic Au nanorod arrays can be grown by electrodeposition in Au-backed nanoporous alumina templates using polyethylenimine (PEI) as an adhesion layer, with excellent height control between 300 nm and 1.4 microm. The local height distribution can be extremely narrow with relative standard deviations well below 2%. The uniform growth rate appears to be determined by the adsorbed PEI matrix, which controls the growth kinetics of the grains comprising the nanorods. The nanorods can be retained as free-standing 2D arrays after careful removal of the AAO template. Reflectance spectroscopy reveals a collective plasmon mode with a maximum near 1.2 microm, in accord with recent calculations for 2D arrays of closely spaced cylindrical nanoparticles.