Quantum Engineering of Single-Crystalline Silver Thin Films.

There is a demand for the manufacture of ultra low-loss metallic films with high-quality single crystals and surface for quantum optics and quantum information processing. Many researches are devoted to alternative materials, but silver is by far the most preferred low-loss material at optical and near-IR frequencies. Usually, epitaxial growth is used to deposit single-crystalline silver films, but they still suffer from losses and well-known deweting effect. Here we report the two-step approach for e-beam evaporation of atomically smooth single-crystalline metallic films. The proposed method is self-controlled by quantum size effects and is based on the step switch of film growth kinetics between two deposition steps, which allow to overcome the film-surface dewetting. Here we have used it to deposit 35-100 nm thick single-crystalline silver films with sub-100 pm surface roughness and extremely low losses. We anticipate that the proposed approach could be readily adopted for the synthesis of other low-loss single-crystalline metallic thin films.