Self-Assembly of Carbon Black/AAO Templates on Nanoporous Si for Broadband Infrared Absorption

Broadband absorption in the mid-infrared region is of significance for wide applications, such as photo/thermal detection, infrared stealth, and thermal imaging. Recently, metal-based plasmonic absorbers have been developed in the mid-infrared region. However, the fabrication cost, thickness, and bandwidth of these absorbers applied in aerospace still need to be improved. In this study, we propose and experimentally demonstrate a large-area, rather thin, metal-free absorber with broadband mid-infrared absorption based on a low-cost self-assembly process. The metal-free absorber is fabricated by spraying carbon black nanoparticles onto 5 μm-thick transferrable anodic aluminum oxide (AAO) templates on nanoporous Si graded-index films, which are fabricated by ion irradiation. Experimental results show that the average absorbance can reach 97.5% in the range of 2.5-15.3 μm. Full-wave numerical simulations show that the electromagnetic fields are greatly enhanced into pores, as these random carbon black particles serve as scatter centers and couple light into 5 μm-thick AAO templates, enhancing the interaction of light with carbon black significantly, and reveal that the high-performance broadband absorption is attributed to the light-trapping effect. The significant light absorption combined with a low-cost, high-production self-assembly technique suggests that the absorber can be used in the fields of optoelectronics and integrated photonics.