Structure Dependent Broadband Optical Absorption in Carbon Nanotubes

Near-perfect black surfaces are desirable in many applications, including from space telescopes and satellites to energy harvesting and biomedical devices. Carbon nanostructures have emerged as potential candidates for fabricating ultrablack optical absorbers. Here, we have studied the structure-dependent light absorption capacity of carbon nanotubes in the broadband region of UV–vis–NIR. Four types of carbon nanotube (CNT) structures, noodle CNTs, spring CNTs, vertically aligned carbon nanotubes (VACNTs), and flower carbon nanotubes (FCNTs), are fabricated using the thermal chemical vapor deposition (CVD) technique. The light-trapping capacity of noodle CNT, spring CNT, VACNT, and FCNT is ≥94%, ≥95%, 98%, and ≥99.97%, respectively, in the UV–vis–NIR wavelength range. Varying the absorption of incident radiation in CNTs has been attributed to various structure-dependent parameters such as multiple scattering, light trapping sites, multiple length scales, and optical path length. It is shown that hierarchical structure imparts near perfect blackbody characteristics (absorption, >99.98%; emissivity, −0.98) to FCNTs. In addition, the superhydrophobic and self-cleaning behavior of VACNTs and FCNTs makes them suitable candidates for solar and antibacterial applications.