Investigating the infrared spectral radiative properties of self-ordered anodic aluminum oxide for passive radiative heat dissipation

Nanoporous self-ordered anodic aluminum oxide (AAO) film has shown great promise for applications in passive radiative heat dissipation due to its high infrared thermal emissivity and its good economic efficiency for mass production. However, the passive radiative cooling mechanism of AAO is not yet fully understood. In this study, the finite-difference time-domain (FDTD) method is adopted to theoretically investigate how the structure of AAO, pore diameter, interpore distance, porosity, and thickness included, impact its infrared spectral emissivity for radiative cooling. The results demonstrate that the infrared spectral emissivity of AAO film is mainly in-fluenced by the porosity and the film thickness. There exists an optimal porosity for a certain film thickness to obtain the maximum infrared emissivity. When the difficulty in practical fabrication of thick AAO film is con-sidered, the ideal AAO film thickness locates between 50 and 100 mu m. The results reported in this study can be exploited to guide the design and development of high-emissivity passive radiative cooling materials.