Silicon-air nanofilm based on the ⟨110⟩ projection of a diamond lattice to enhance radiative cooling.

This article focuses on the development, fabrication, and characterization of a silicon-air ultrathin nanofilm photonic crystal based on the ⟨110⟩ surface-terminated projection of a diamond lattice, designed to target the atmospheric transparent window between 8 and 13 micrometers for applications such as passive radiative cooling. The authors employed reactive ion etching to create air holes in silicon wafers, producing a structure exhibiting broadband spectral selectivity with high reflectivity in the visible range and high emissivity in the mid- to long-wavelength infrared range. Experimental reflectance measurements using Fourier-transform infrared and spectrophotometer techniques showed reasonable agreement with simulations performed via the Stanford Stratified Structure Solver, validating the design's optical properties. The study suggests that further improvements, including antireflective coatings and deeper etching, could enhance performance, and that this nanofilm could serve as a baseline for more advanced three-dimensional photonic crystal structures for thermal management and optical applications.