Smooth Sidewalls on Crystalline Gold through Facet-Selective Anisotropic Reactive Ion Etching: Toward Low-Loss Plasmonic Devices.

Quantum plasmonics aims to harness the deeply subwavelength confinement provided by plasmonic devices to engineer more efficient interfaces to quantum systems in particular single emitters. Realizing this vision is hampered by the roughness-induced scattering and loss inherent in most nanofabricated devices. In this work, we show evidence of a reactive ion etching process to selectively etch gold along select crystalline facets. Since the etch is facet selective, the sidewalls of fabricated devices are smoother than the lithography induced line-edge roughness with the prospect of achieving atomic smoothness by further optimization of the etch chemistry. This opens up a route toward fabricating integrated plasmonic circuits that can achieve loss metrics close to fundamental bounds.