Enhancing Chemical and Optical Stability of Silver Nanostructures by Low-Temperature Hydrogen Atoms Processing

A large variety of applications ranging from plasmonic sensing to plasmonic enhanced solar cells, photonics, and optics can benefit from a reliable method to enhance chemical and time stability of silver-based plasmonic nanostructures and metamaterials. Therefore, here we demonstrate and discuss the effectiveness of a low-temperature (100 °C) hydrogen atom processing of silver to inhibit its oxidation and stabilize surface plasmon resonances in silver nanostructure suitable for plasmonics, metamaterials, sensing, and photovoltaics. Interestingly, no dielectric overlayer encapsulating Ag is used to protect the silver nanostructure, differently from the common approach, because these overlayers typically lead to a red shift of the optical resonances due to their refractive index. Conversely, we demonstrate that the silver deoxidation by the hydrogen treatment results in a slight blue shift of resonances, which is useful for preserving resonances in the visible range. The chemical mechanism rationalizing the validity of this processing is discussed. The optical properties of the fabricated samples were measured by means of transmission, reflection, and ellipsometry spectroscopies. Theoretical support to the interpretation of the optical properties demonstrates the advantages of this advanced processing. Therefore, this work is an important step toward novel and breakthrough applications of stable silver-based nanostructures for plasmonics and metamaterials exploiting visible light.