Carbon-Nanotube-Based All-Dielectric Near-Infrared Perfect Absorbers

Achieving sharp and strong near-infrared (NIR) absorption of thin films is important for various optical devices. Herein, we demonstrate the design and fabrication of an all-dielectric NIR absorber with near unity absorptance based on the strong exciton resonance of structure-sorted semiconducting single-walled carbon nanotube (SWCNT) ultrathin films. Previous studies of perfect absorbers have mainly focused on fine-structured designs such as photonic crystals and metasurfaces. However, these designs face scalability and thermal stability challenges. We fabricate SWCNT-based all-dielectric NIR near-perfect absorbers with a simple planar layered structure. This design is inspired by the Salisbury screen typically used for electromagnetic waves at considerably longer wavelengths. Beyond the conventional Salisbury screen structure, all-dielectric planar absorber design in the NIR can be achieved owing to both high absorption and reflection of the SWCNT thin films due to the distinct exciton resonance. The theoretical and experimental results show nearly perfect absorption at the first exciton resonance wavelength of structure-sorted SWCNTs in the planar four-layer structure. The proposed absorber structure offers resonant wavelength tunability simply by selecting the structure of SWCNTs, robustness against unexpected variations in film thicknesses during fabrication processes, and the potential for scalability and thermal stability.