Super black iron nanostructures with broadband ultralow reflectance for efficient photothermal conversion

Structural absorption is widely accepted as an effective way to produce super black materials, which show matte black appearance and extremely broadband low reflectance. We have developed an ultrafast pulsed laser deposition (PLD) technology to deposit thin super black film by tuning the surface microstructure. Various coatings made by Fe, Al and Ti all showed broadband absorption, confirming that the PLD method is suitable for fabricating super back materials. At the wide range of wavelength from 250 nm to 2000 nm, the total integrated reflectance of iron coating is ~1.2%. The super black iron surface coating has low volume density composed of separated tree-like aggregates of nanoparticles. We have demonstrated that low effective refractive index and multi-layered iron oxide structures are the two contributing factors for the broadband ultralow reflectance. The broadband high-performance film was employed to effectively convert sunlight to heat. The steady-state temperature of the super black surface is 76 °C under solar irradiation.