Black aluminum, distinguished by its highly porous columnar structure, exhibits exceptional optical properties, making it valuable for applications like light trapping, infrared detection, and passive radiative cooling. This study compares the structural and optical characteristics of black aluminum with traditional reflective aluminum layers of varying thicknesses, all deposited on fused silica substrates. Optical analysis, corroborated by COMSOL simulations, demonstrates that black aluminum's unique structure significantly reduces visible light reflectivity and enhances emissivity in the near- and mid-infrared regions. This enhanced emissivity is attributed, in part, to aluminum nitride (AlN) grain boundaries and a surface oxide layer. Compared to reflective aluminum, black aluminum shows a reflectivity below 5% in the visible spectrum and an average emissivity of 0.4–0.5 in spectral range between 1.2 μm and 20 μm. Furthermore, it exhibits approximately ten times lower thermal conductivity and double the volumetric heat capacity, differences stemming from its porous morphology, nanoscale crystallites, and the presence of aluminum nitrides and oxides.
This work was honoured by its selection as the cover art for Volume 41, Issue 6 of the journal.