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 user-defined direction. A nanocup is a plasmonic nanoparticle that supports magneto-inductive 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 three-dimensional nano-antenna, allowing the user to control light at the nano-scale. 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.