Plasmonic Biomimetic Nanocomposite with Spontaneous Subwavelength Structuring as Broadband Absorbers

Broadband plasmonic absorbers are essential components for photovoltaic, photothermal, and light-emitting devices. They are often made by lithographic processes that impart out-of plane surface features with subwavelength dimensions to metallic films. However, lithographic subwavelength patterning of inexpensive plasmonic ceramics, such as TiN, is challenging because of high temperature processing and the chemical robustness of these materials. In this work, we show that layer-by-layer assembly (LbL) of TiN plasmonic nanoparticles with polyelectrolytes results in spontaneous formation of out-of-plane topography with subwavelength dimensions. The columnar morphology of these corrugated coatings and their plasmonic functionality results in broadband absorption capabilities exemplified by 90% of the light from the ultraviolet to infrared parts of the spectrum being absorbed. The method is applicable to large, flexible, and conformal surfaces with complex geometry. It is also fast, scalable, and environmentally friendly. LBL processing of TiN nanoparticles demonstrates the possibility of replacement of lithographic patterning with stochastic self-assembly processes in manufacturing of photonic metasurfaces.