Anisotropic perfect absorber with borophene-based metasurface at near-infrared wavelengths

Two-dimensional material-based perfect absorbers have attracted considerable attention in nanophotonics owing to their tunable optical responses and strong light-matter interactions. However, many previously reported optical absorbers rely on complex nanostructures and etching processes, which not only increase fabrication difficulty but also limit tunability and practical integration. In this paper, we propose a borophene-based anisotropic perfect absorber featuring a simple configuration without complicated etching steps. By exploiting the strong anisotropic plasmonic response of borophene, dual-band perfect absorption is achieved under the critical coupling condition at 147.90 THz and 203.05 THz, with absorptions of 99.9% for both peaks. The near-perfect absorption at what we believe to be the first resonance peak mainly originates from the borophene localized surface plasmon resonance, whereas the second resonance peak arises from a hybrid plasmonic mode involving both the borophene localized surface plasmon response and the borophene surface plasmon response. These plasmonic modes significantly enhance the localized electric field and strengthen the light-borophene interaction. When the borophene orientation is rotated by 90°, two weak absorption peaks of 26.6% and 28.6% are obtained at 77.79 THz and 106.13 THz, respectively, confirming the strong anisotropic absorption behavior. The absorber also maintains high absorption for both resonance peaks as the incident angle increases from 0° to 60°, showing good angular tolerance. Our design provides a promising approach for developing high-performance absorbers and tunable anisotropic photonic devices.