Optically processed microlens array for single-beam lithography of plasmonic structures

Abstract

A 2D dielectric grating produced by photolithography was employed as a microlens array (MLA), which was based on a smooth surface and a shape that may be defined roughly as a hemisphere of each lattice. Such a 2D MLA can focus an incident ultraviolet light beam into a matrix of light spots, which were estimated to be as small as 500 nm in diameter. Using a thin layer of photoresist (PR) to record the pattern of the focusing spots, we achieved an approximately inversed structure of periodically arranged holes in PR in submicron sizes. Filling these holes with gold using chemically synthesized colloidal gold nanoparticles produced a plasmonic grating consisting of gold nanoparticles larger than 580 nm in average diameter. Localized surface plasmon resonance in both first and second orders was observed, which was verified by the spectroscopic response and theoretical simulations. MLA can be thus repeatedly used as a master to produce plasmonic photonic structures with high reproducibility.

Keywords

• dipolar and quadrupolar plasmons
• localized surface plasmons
• metallic photonic structures
• microlens array
• photolithography