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

The George W Woodruff School of Mechanical Engineering, Georgia Institute of Technology, Atlanta, GA 30332, USA.
Nanotechnology (Impact Factor: 3.82). 06/2009; 20(21):215704. DOI: 10.1088/0957-4484/20/21/215704
Source: PubMed


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

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Available from: Xiaojia Wang, May 14, 2015
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    • "J/cm 2 . The projected ranges of hydrogen and carbon ions in a target MWCNT layer with a density of 0.2 g/cm 3 [23] [24] were estimated (using SRIM [25]) to be 24.8 lm and 5.75 lm, respectively. "
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    • "Vertically-aligned carbon nanotubes (VACNT) have been measured to be the blackest known substance [1] [2] [3] [4]. However, typical VACNT samples are not perfect absorbers and often tend to increase in reflectance at short wavelengths [1] [5] [6] and appear specular at large viewing angles. The reflectance of VAC- NT depends on many variables – including density, height, uniformity, and alignment [5,7–9]. "
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    • "Although the gold nanoparticles are able to serve as an efficient optical absorber, the energy conversion efficiency is still low and the opto-acoustic pressure is unable to satisfy the level of energy intensity that is required for therapeutic purposes [7]. Recently, many researchers reported that the vertically aligned CNTs appeared as a perfect black body as they could absorb light of a wide range of wavelengths [11] [12] [13] [14] [15]. For this reason, it follows naturally that a system of aligned CNTs is a perfect candidate to generate acoustics through the optoacoustic technique. "
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