. § These authors contributed equally to this work.T he interaction of electromagnetic fields with metallic nanostructures can produce collective oscillations of the conduction electrons at metalϪdielectric interfaces. These oscillations are known as localized surface plasmon resonances (LSPRs) and propagating surface plasmon polaritons (SPPs) and are responsible for most of the phenomena in the field of plasmonics. 1 Two-and threedimensional arrays of metallic nanostructures could play key roles in functional materials. Optical filters, 2,3 substrates for optical detection of chemical and biological analytes using LSPRs 4 or surface-enhanced Raman scattering (SERS), 5Ϫ7 substrates for enhanced luminosity, 8 materials to augment absorption in thin-film photovoltaic devices, 9,10 metamaterials 11,12 with negative magnetic permeabilities 13 and negative refractive indices, 14 and surfaces for perfect lenses 15 and invisibility cloaking 16 are examples of possible and realized applications. There are, however, significant technical challenges in generating arbitrary patterns of metallic, dielectric, and semiconducting nanostructures for research and for potential commercial devices. The most sophisticated patterns are fabricated using electron-beam lithography (EBL), 17 focusedion beam (FIB) milling and lithography, 14 or direct laser writing. 18 These techniques can generate nearly arbitrary patterns in resists (e.g., EBL) or hard materials (e.g., FIB milling), but they are serial, expensive, and require access to a cleanroom.A number of techniques have emerged that have begun to address the challenges associated with conventional scanningbeam lithographic tools. 19 Xia and coworkers recently reviewed synthetic methods that can produce large quantities of high-quality metallic structures for plasmonic applications. 20 These materials, however, are difficult to arrange in the ordered arrays that are required for many applications in optics. 21 Van Duyne and co-workers have developed an approach to generate ordered arrays of metallic particles called "nanosphere lithography", which uses a monolayer of colloidal crystals as a stencil mask; the triangular voids direct the deposition of metal on the substrate by evaporation. 22 Giessen and co-workers used the same voids as apertures through which to produce split-ring resonators by rotating the substrate at an angle during evaporation. 23 The laboratories of Rogers, Odom, Nuzzo, and others have used soft lithographic processes to fabricate large-area patterns of metallic nanostructures.