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We found an appropriate growth time is necessary for the synthesis of a super-aligned carbon nanotube array

Controlled growth of super-aligned carbon nanotube arrays for spinning continuous unidirectional sheets with tunable physical properties.

NANO LETTERS, no. 2 (2008): 700-705

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摘要

We report controlled syntheses of super-aligned carbon nanotube (CNT) arrays with the desired tube-diameter, number of walls, and length for spinning continuous unidirectional sheets to meet a variety of industrial demands. The tube-diameter distribution of super-aligned arrays is well controlled by varying the thicknesses of catalyst fil...更多

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简介
  • The authors report controlled syntheses of super-aligned carbon nanotube (CNT) arrays with the desired tube-diameter, number of walls, and length for spinning continuous unidirectional sheets to meet a variety of industrial demands.
  • The authors present the progress in tuning the physical properties of as-produced unidirectional CNT sheets by controlling the tube-diameter and the length of super-aligned CNT arrays.
重点内容
  • We report controlled syntheses of super-aligned carbon nanotube (CNT) arrays with the desired tube-diameter, number of walls, and length for spinning continuous unidirectional sheets to meet a variety of industrial demands
  • Super-aligned carbon nanotube (CNT) arrays are distinguished from ordinary vertically aligned CNT arrays by their “super-aligned” nature, that is, the CNTs in super-aligned arrays have a much better alignment than those in ordinary arrays (Figure 1), which is a consequence of the narrower diameter distribution and higher nucleation density.[1,2]
  • One fact remains to date: the only synthesized super-aligned CNTs suitable for drawing sheets with are multiwalled CNTs (MWCNTs) with a relatively large tube-diameter of 10∼15 nm.[1,2,3,4,5,6]
  • We investigated the physical properties of unidirectional CNT sheets drawn from CNT arrays with different tube-diameters and lengths
  • The sheet resistivity, the optical transmittance, and the degree of polarized light emission all decrease with increasing the length of CNT arrays, which may be ascribed to the bundling effect discussed below
  • We found an appropriate growth time is necessary for the synthesis of a super-aligned CNT array
结果
  • The sheet resistivity, the optical transmittance, and the degree of polarized light emission all decrease with increasing the length of CNT arrays, which may be ascribed to the bundling effect discussed below.
  • By varying the tube-diameter, the number of walls and the length of super-aligned CNT arrays as mentioned above, the authors are able to tune the electrical and optical properties of as-produced unidirectional CNT sheets, which will further facilitate different applications such as transparent conducting films (TCFs) with different sets of transparency and resistivity.
  • The negative temperature dependence of sheet resistance obeys the three-dimensional variable range hopping mechanism, following the equation R ) R0T1/2 exp(T0/T)1/4 (Supporting Information, Figure S4), similar to the electrical conduction behavior of twisted yarns.[13] In addition, as shown in the middle and bottom groups of curves, the temperature dependence of the normalized resistance is not in turn heavily dependent on the length of arrays synthesized from a given film.
  • Previous study in the group has shown that, due to increasing the number of contact points, the shrunk yarns have a much lower resistance compared to the unshrunk sheets.[15] Electron transport at these contact points gives rise to random directions of electric field of radiation, which breaks the polarization induced by the electron transport along CNTs and reduces the polarization degree.
  • This can be further shown by the fact that if the authors use O2 plasma to reduce the length of a super-aligned array and remove a layer of CNTs, the array can still give rise to unidirectional sheets well.
  • The authors have been able to control the tubediameter and the length of super-aligned CNT arrays and, as a result, to tune the physical properties of as-produced unidirectional sheets.
结论
  • A new model describing the drawing process is proposed to explain the fact that a sheet produced from a longer array consists of larger bundles, which causes a reduction of sheet resistivity, transmittance, and polarization degree with increasing array length.
  • Supporting Information Available: Illustration of experimental setup, tube-diameter histogram of one sample, TGA curves, fitting curves of electrical conduction, transmittance curves for the visible band, and a typical SEM image of the super-aligned CNT array.
总结
  • The authors report controlled syntheses of super-aligned carbon nanotube (CNT) arrays with the desired tube-diameter, number of walls, and length for spinning continuous unidirectional sheets to meet a variety of industrial demands.
  • The authors present the progress in tuning the physical properties of as-produced unidirectional CNT sheets by controlling the tube-diameter and the length of super-aligned CNT arrays.
  • The sheet resistivity, the optical transmittance, and the degree of polarized light emission all decrease with increasing the length of CNT arrays, which may be ascribed to the bundling effect discussed below.
  • By varying the tube-diameter, the number of walls and the length of super-aligned CNT arrays as mentioned above, the authors are able to tune the electrical and optical properties of as-produced unidirectional CNT sheets, which will further facilitate different applications such as transparent conducting films (TCFs) with different sets of transparency and resistivity.
  • The negative temperature dependence of sheet resistance obeys the three-dimensional variable range hopping mechanism, following the equation R ) R0T1/2 exp(T0/T)1/4 (Supporting Information, Figure S4), similar to the electrical conduction behavior of twisted yarns.[13] In addition, as shown in the middle and bottom groups of curves, the temperature dependence of the normalized resistance is not in turn heavily dependent on the length of arrays synthesized from a given film.
  • Previous study in the group has shown that, due to increasing the number of contact points, the shrunk yarns have a much lower resistance compared to the unshrunk sheets.[15] Electron transport at these contact points gives rise to random directions of electric field of radiation, which breaks the polarization induced by the electron transport along CNTs and reduces the polarization degree.
  • This can be further shown by the fact that if the authors use O2 plasma to reduce the length of a super-aligned array and remove a layer of CNTs, the array can still give rise to unidirectional sheets well.
  • The authors have been able to control the tubediameter and the length of super-aligned CNT arrays and, as a result, to tune the physical properties of as-produced unidirectional sheets.
  • A new model describing the drawing process is proposed to explain the fact that a sheet produced from a longer array consists of larger bundles, which causes a reduction of sheet resistivity, transmittance, and polarization degree with increasing array length.
  • Supporting Information Available: Illustration of experimental setup, tube-diameter histogram of one sample, TGA curves, fitting curves of electrical conduction, transmittance curves for the visible band, and a typical SEM image of the super-aligned CNT array.
基金
  • The work was supported by the National Basic Research Program of China (2005CB623606) and NSFC (10704044, 10721404)
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