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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    ABSTRACT: On the basis of spectra obtained through the X-ray Auger-electron spectroscopy (XAES) of carbon (C KVV) and X-ray photoelectron spectroscopy (XPS) of the carbon valence band using the equipment of the Russian–German beam line of the synchrotron radiation facility BESSY II and a Kratos Axis Ultra DLD analytical system, the influence of pulsed ion radiation on the ratio of sp2/sp3-hybridized orbitals of carbon atoms in layers of oriented multi-walled carbon nanotubes (MWCNTs) is investigated. It is shown that when the MWCNTs are subjected to ten pulses, a substantial increase in the proportion of carbon atoms in the sp3 hybridization state occurs compared with MWCNTs subjected to a single pulse. This increase is associated with the formation of thin (<10 nm) nanotubes and onion-like carbon, inside which masses of nanodiamond structures are observed in some cases.
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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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    Carbon 08/2014; 74:329–332. DOI:10.1016/j.carbon.2014.03.040 · 6.20 Impact Factor
    • "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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    ABSTRACT: A new model of high-intensity focused ultrasound generation by radiation from a composite nanothinfilm made of carbon nanotubes (CNTs) and elastomeric polymer is presented in this paper. The composite nanothinfilm is deposited to the surface of a concave lens and the performance of focused ultrasound generated by an incident pulsed laser onto the lens is analyzed. The analysis and results are verified by comparing with published experimental data and very good agreement is recorded. The opto-acoustic pressure on the symmetric axis and the lateral focal plane are investigated analytically and the result indicates that excellent acoustic performance is found to be present in the vicinity of the focus region. The temporal performance of the focused lens is also investigated both at the focal point and the prefocal zone and very good agreement comparing with experiment is obtained. Conclusively, it is demonstrated theoretically that there exists an optimal input frequency for a pulsed laser at which the performance of the focused lens can be tremendously enhanced. In general, this new analytical model provides new guidelines in the design of high-intensity ultrasound lens, hence opening up promising applications to medical ultrasonography treatment.
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