From rings to crescents: a novel fabrication technique uncovers the transition details.

A novel fabrication route is reported for the generation of substrate-supported symmetric and asymmetric metal nanostructures. We combine a colloidal template and angled evaporation to deposit in situ mask materials for subsequent lithographic pattern transfer. The technique is demonstrated for the fabrication of concentric and nonconcentric gold rings and crescents. Optical properties of localized plasmon resonances in such structures are studied by UV-vis-NIR spectroscopy and finite-difference time domain simulations during the transition from rings to crescents revealing the development of strong quadrupolar modes.