Abstract
Optical superabsorbers use nanostructures to achieve very high levels of optical absorptivity and emissivity across a wide range of wavelengths and angles of incidence. This makes them ideally suited for a wide range of applications in energy management and scavenging, including architectural and domestic heating and cooling. These absorbers feature absorptivity and emissivity values that are typically within a small fraction from the ideal Planck blackbody equation. Here, vertically aligned multiwalled carbon nanotube forest superabsorbers were grown on sapphire to determine their optical properties, particularly in the infrared. The propagation of electromagnetic radiation along the forests was modeled in order to reveal the absorption mechanisms that lead to such high levels of absorption, which up to now, remain poorly understood. The model suggests the absorption mechanism is strongly linked to the in-plane electrical conductivity of the nanotubes and is largely independent of the through-plane conductivity. This is counterintuitive as the through-plane conductivity is parallel to the electric-field vector of the incident wave. The radiative heating/cooling performance of such superabsorber coupled to a hypothetical thermoelectric device is also modeled to assess its environmental capacity for heat management within a domestic/office setting.