CNT array

In theory, an ideal black coating or absorber would be able to completely absorb light over a broadband wavelength range regardless of the incident angle or polarization. Most naturally occurring materials show specific reflections, mainly due to their composition and structure...

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In theory, an ideal black coating or absorber would be able to completely absorb light over a broadband wavelength range regardless of the incident angle or polarization. Most naturally occurring materials show specific reflections, mainly due to their composition and structure, resulting in a refractive index higher than that of the surrounding air or vacuum. Therefore, the key to the experimental realization of an ideal absorber is to reduce the surface refractive index to unity and eliminate its optical reflection as much as possible. In the current situation, it is believed that nothing can compare with vertically aligned carbon nanotube (VACNT) arrays in terms of obtaining uniform absorbers over a wide wavelength range, which are reported to exhibit ultra-high absorptivity of more than 99.95%. Due to the intrinsic optical properties and unique nanostructure morphology of carbon nanotubes (CNTs), the refractive index (n) of VACNT arrays is very similar to that of air, resulting in very low reflectivity at the air electrical interface. More importantly, the excellent performance of carbon nanotube arrays as absorbers provides ideas for the design and preparation of perfect absorbers. The inherent absorption properties of carbon materials indicate that the design and preparation process of surface micro-nanostructures are the key to determining the absorption performance in practical applications. In addition to carbon nanomaterial coatings, other black coating methods include surface anodization, chemical etching, and spraying black coatings. However, the absorption performance of these methods over a wider wavelength range cannot be compared with that of carbon nanotube materials.

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