Subwavelength proximity nanolithography using a plasmonic lens

This article presents a novel device, the plasmonic lens (PL), consisting of equally spaced ring apertures in a metal film deposited on a fused silica substrate. It was fabricated by electron-beam lithography (EBL) and reactive-ion etching (RIE). When illuminated by a collimated laser, a cylindrical surface plasmon (SP) is excited in the PL, scattered by the structure, and propagates. As a result, the PL focuses a subwavelength spot in the midfield, i.e., the focal length is several microns. The authors experiment demonstrated that 90-300 nm spots (up to lambda/4) with pitches of 400-500 nm, focal length of 1.7 mu m, were printed by a PL using 405 nm laser. The authors three-dimensional electromagnetic simulation predicted a full width at half maximum (FWHM) of 210 nm, equivalent to an aberration-free lens having an unity numerical aperture (NA=1). The experimental result agreed well with the simulation. A theoretical model is also presented. Given its small footprint and subwavelength resolution, the PL holds great promise in direct-writing and scanning microscopy. (c) 2007 American Vacuum Society.