Atomically thin planar metasurfaces

Enhancing light absorption in two-dimensional (2-D) materials using simple planar structures is important for the development of large-area atomic-scale photonic devices but also has been a major challenge. We theoretically present a general strategy to create an atomically thin planar metasurface consisting of a semiconductor monolayer (replacing the array of subwavelength elements in classical metasurfaces), a transparent spacer, and a metallic back reflector, to achieve near-perfect, polarization-sensitive absorption in 2-D materials. This strategy is validated by experimentally demonstrating planar metasurfaces based on atomically thin Ge films. Higher than 90% exclusive absorption, 2.5 times greater than prior demonstration, is achieved in the MoS2 monolayer for TE polarization. Our strategy can be extended to the infrared spectrum and thus has potential for thermal energy applications.