Evolutionary selection growth of silver films for low-loss nanophotonic devices

When talking about nanophotonics, quantum computing and sensing high-quality factor plasmonic devices are playing crucial role. In most cases for making such devices one has to use non-lattice matched or transparent amorphous substrates. Plasmonic devices quality factor is mainly determined by ohmic losses, scattering losses at grain boundaries, and in-plane plasmonic scattering losses of a metal – substrate system. We demonstrate here the e-beam evaporation method to deposit ultralow-loss silver thin films on transparent lattice-mismatched substrates. This process corresponds to evolutionary selection growth mode. The key feature of our approach is a precise control during the whole process consisting of film deposition on a cold substrate, self-crystallization and subsequent annealing for stress relaxation. In particular, the stress relaxation leads to further grains growth. We are able to deposit 100 nm thick polycrystalline silver films with micrometer-scale grains, low roughness and ultralow optical losses. Finally, we show ultrahigh-quality factor plasmonic silver nanostructures on transparent lattice-mismatched substrate. This can be of the great interest for high performance and single-molecule optical sensors applications.