Silver-based plasmonics: golden material platform and application challenges [Invited]

A novel material platform based on metallic thin films with ultra-low losses in the visible and near-IR range is crucial for rapid development of a wide range of new generation plasmonic devices. For many years silver has been known as potentially the best plasmonic material with the naturally lowest ohmic losses at optical frequencies. However, the widespread implementation of the silver-based material platform for plasmonics and metamaterials is limited due to technological challenges in thin film synthesis and nanoscale features fabrication techniques. This review describes the main types of silver-based plasmonic devices from the thin films point of view required for their widespread practical application. Based on comparative analysis of more than 60-year-long history of previously reported data for the silver thin films, the authors formulate the qualitative and quantitative criteria of "ideal" silver film (which the authors name the silver "dream" plasmonic film) for plasmonic devices with ultra-low loss. This paper outlines on several well-known metrology issues in plasmonic metallic films characterization and summarize the set of methods for their properties careful and precise extraction. Finally, the detailed analysis of silver synthesis techniques and quantitative comparison of the achieved silver properties is carried out.