ABSTRACT
Because the shape of large (>100 nm) metallic particles is often difficult to control by synthetic methods, fabrication techniques have been pursued as an alternative approach. Top-down procedures can fabricate metal structures with anisotropic shapes and with optical properties tunable from 500 to 3000 nm4, 12. Serial patterning techniques such as electron beam lithography can generate structures with arbitrary sizes and shapes in 2D13, 14, although low throughput and small writeareas (hundreds of square microns) are current challenges. Besides direct-writing methods, templates have also been used to produce particles with anisotropic shapes. Isolated sub-micron spheres and closepacked sphere arrays have acted as templates onto which metals were deposited to obtain particles with crescent-like15, 16 and triangular shapes17, respectively. Anodized aluminum oxide membranes are another widely used template for producing nanorods as long as 10 μm18. Recently, we developed a template-based approach to fabricate metallic pyramidal shells with smooth facets and sharp tips (r < 2 nm)19.
