(310a) Gold Nanocrescents with Highly Tunable Infrared Plasmonic Properties Fabricated by Nanosphere Template Lithography

Gold crescent-shaped nanostructures with uniform size and orientation were fabricated using nanosphere template lithography. The nanocrescents have broadly tunable (900-4050 nm) and strong plasmon resonances (effective cross sections up to 30) in the infrared (IR) spectral region. The plasmon resonances in the crescents have been shown to be sensitive to the dielectric environment with shifts of the plasmon resonance peak position of up to 880nm/RIU. We will present a new approach to investigate the tunability of nanocrescent plasmons in the IR based on controlling the distance between the tips of the open crescent structures. This approach involves rotational nanosphere template lithography when both the angle of deposition and the angle of rotation between subsequent metal depositions are controlled to produce nanocrescents of tunable in-plane aspect ratio and circumference angle. The tip-to-tip distances in the nanocrescents are varied until continuous rings are formed. The number of plasmon resonance peaks in the IR increases from two for completely open crescents to four peaks for closed, continuous crescents. The magnitude of those resonances is dependent upon the orientation of the nanocrescents with respect to the polarization of the incident light. The ability to tune the crescent plasmon resonances farther into the IR by using substrates with higher refractive indices (e.g., from a refractive index of ~ 1.5 for glass to ~3.4 for silicon) is being explored.