Beyond single-crystalline metals: ultralow-loss silver films on lattice-mismatched substrates

TL;DR

This paper introduces a novel deposition method for ultralow-loss silver films on lattice-mismatched substrates, enabling high-quality plasmonic devices with potential applications in sensing and quantum technologies.

Contribution

It presents an evolutionary selection growth technique for depositing high-quality silver films on mismatched substrates, enhancing plasmonic device performance.

Findings

Achieved ultralow optical losses in 100-nm thick silver films.

Produced polycrystalline silver films with micrometer-scale grains.

Demonstrated high-quality plasmonic nanostructures comparable to epitaxial silver.

Abstract

High-quality factor plasmonic devices are crucial components in the fields of nanophotonics, quantum computing and sensing. The majority of these devices are required to be fabricated on non-lattice matched or transparent amorphous substrates. Plasmonic devices quality factor is mainly defined by ohmic losses, scattering losses at grain boundaries, and in-plane plasmonic scattering losses of a metal - substrate system. Here, we demonstrate the deposition technique to e-beam evaporate ultralow-loss silver thin films on transparent lattice-mismatched substrates. The process is based on evolutionary selection growth. The key feature of our approach is a well-defined control of deposition on a cooled substrate, self-crystallization and subsequent annealing for precise stress relaxation that promote further grains growth. We are able to deposit 100-nm thick ultraflat polycrystalline silver films with micrometer-scale grains and ultralow optical losses. Finally, we show ultra-high-quality factor plasmonic silver nanostructures on transparent lattice-mismatched substrate comparable to epitaxial silver. This can be of the great interest for high performance or single-molecule optical sensorics applications.