Visible and near-infrared radiative properties of vertically aligned multi-walled carbonnanotubes

Abstract

This work investigates the reflection and scattering from vertically aligned carbon nanotubes,fabricated on silicon substrate using thermally enhanced chemical vapor deposition withboth tip-growth and base-growth mechanisms. The directional–hemispherical reflectance inthe visible and near-infrared wavelengths was measured with an integrating sphere. Thepolarization-dependent bidirectional reflectance distribution function was characterizedwith a laser scatterometer at the wavelength of 635 nm. The effective medium theory wasused to elucidate the mechanism of high absorptance (greater than 0.97 in the spectralregion from 400 to 1800 nm) of the multi-walled carbon nanotube samples. It is observedthat scattering by impurities on the top of the nanotubes, by the nanotube tips,and by defects and misalignment can significantly increase the reflectance andintroduce retroreflection. This study may facilitate application of carbon nanotubes inpyroelectric detectors as well as thermophotovoltaic emitters and absorbers.