Template-Free Growth of Well-Ordered Silver Nano Forest/Ceramic Metamaterial Films with Tunable Optical Responses.

Currently, the limitations of conventional methods for fabricating metamaterials composed of well-aligned nanoscale inclusions either lack the necessary freedom to tune the structural geometry or are difficult for large-area synthesis. In this Communication, the authors propose a fabrication route to create well-ordered silver nano forest/ceramic composite single-layer or multi-layer vertically stacked structures, as a distinctive approach to make large-area nanoscale metamaterials. To take advantage of direct growth, the authors fabricate single-layer nanocomposite films with a well-defined sub-5 nm interwire gap and an average nanowire diameter of ≈3 nm. Further, artificially constructed multilayer metamaterial films are easily fabricated by vertical integration of different single-layer metamaterial films. Based upon the thermodynamics as well as thin film growth dynamics theory, the growth mechanism is presented to elucidate the formation of such structure. Intriguing steady and transient optical properties in these assemblies are demonstrated, owing to their nanoscale structural anisotropy. The studies suggest that the self-organized nanocomposites provide an extensible material platform to manipulate optical response in the region of sub-5 nm scale.