Large, Ordered 3D Nanocup Arrays for Plasmonic Applications

A large, ordered nanocup array was fabricated and optically characterized. A novel fabrication method that combined Nanoimprint lithography (NIL), soft lithography, and shadow evaporation was designed to create asymmetric nanoparticles in a large (0.5cm x 1cm) array with subwavelength features. Although this fabrication procedure can be used to create many different types of asymmetric nanostructures that are useful in various plasmonic applications, here we fabricated a periodic nanocup array for redirecting light to a userdefined direction. A nanocup is a plasmonic nanoparticle that supports magnetoinductive coupling between the particle and the incident light. At the resonant frequency, charge oscillation within the nanocup creates a current loop that generates a magnetic field inside the cup. The magnetic field, which travels along the axis of the nanocup, couples with and redirects the incident light regardless of the incident angle. As a result, nanocups can operate as a threedimensional nanoantenna, allowing the user to control light at the nanoscale. As the advancement of fields such as superlenses, optical nanocircuits, and optical cloaking demands the precise control over the geometry and placement of plasmonic nanostructures, this novel fabrication process offers a powerful technique to create a new library of nanoparticles with responses tailored for plasmonic applications.