(Georgia Institute of Technology, 2010-10)
Wang, X. J.; Wang, L. P.; Adewuyi, O. S.; Cola, Baratunde A.; Zhang, Zhuomin
Specular black materials have important applications, such as in absolute cryogenic radiometers, space-borne spectroradiometers, and some energy conversion devices. While vertically aligned carbon nanotubes (VACNT) can have close-to-unity absorptance, so far the reported reflection has been essentially diffuse. This letter describes a highly specular black absorber made of VACNT. Both the bidirectional reflectance distribution function and specular reflectance were measured at the wavelength λ = 635 nm using a laser scatterometer. The ordinary and extraordinary optical constants were obtained by fitting the specular reflectance, calculated from modified reflectance formulae for light incident from air to a uniaxial medium, considering surface roughness. Furthermore, the absorptance at λ = 635 nm was shown to be 0.994±0.002, based on the measured directional-hemispherical reflectance.