Template free growth of robustly stable nanophotonic structures: broadband light superabsorbers

Producing stable ultra-wideband light absorbers by a simple method is challenging for various applications such as solar energy harvesting, thermal regulation and suppression of stray light. Nanostructured refractory materials possess exceptional features enabling them to manipulate incident photons at the subwavelength scale and withstand against severe conditions. Here, we report a sputtering technique-based route to fabricate robustly stable TiAlN black absorbing coatings with a vertically aligned columnar structure, as a unique approach to produce large area metamaterials. The fabrication process is simple, free of any sophisticated patterning approach, substrate-independent, viable and scalable. Robust stability in adverse environments is an exceptional feature of these superabsorbers. Broadband (200-2500 nm) absorption of 89% is achieved from a single TiAlN layer and is increased to 95% after grading with thin anti-reflecting layers. The proposed sputtering based fabrication process would open a new platform to design, prepare and integrate nanophotonic structures, having applications in energy, electronic and optical sectors.