Gold-black manufacture, microstructure, and optical characterization.

Area of Science:

• Nanophotonics and Metamaterials
• Optical Engineering
• Materials Science

Background:

• Gold-black is a nanostructured material known for its broadband absorption properties.
• A prior theoretical model described gold-black's polarization-sensitive spectral absorptance using dipole antenna theory.
• Experimental validation of this theory was lacking, particularly for directional properties.

Purpose of the Study:

• To experimentally validate the first-principle dipole antenna theory for gold-black.
• To measure the polarization-sensitive directional spectral absorptance of gold-black coatings.
• To assess the theory's accuracy across a range of incident angles and wavelengths.

Main Methods:

• Fabrication of gold-black coatings (4- and 8-µm thick) using a custom vapor-deposition cell on a gold substrate.
• Microstructural characterization of the coatings via scanning electron microscopy (SEM).
• Automated measurement of in-plane bidirectional reflectivity at 532 nm and 800 nm for p- and s-polarized light using a reflectometer.

Main Results:

• SEM images revealed the microstructure of the gold-black coatings.
• Bidirectional reflectivity measurements were obtained for incident zenith angles from 10 to 50 degrees.
• Experimental results demonstrated consistency with the predictions of the dipole antenna theory within the measured angular range.

Conclusions:

• The dipole antenna theory successfully predicts the polarization-sensitive directional spectral absorptance of gold-black.
• The experimental validation supports the theoretical framework for understanding light interaction with gold-black nanostructures.
• This work provides a foundation for designing and optimizing gold-black for specific optical applications.