Simien Daneesh, Fagan Jeffrey A, Luo Wei, Douglas Jack F, Migler Kalman, Obrzut Jan
Polymers Division, National Institute of Standards and Technology, Gaithersburg, Maryland 20899, USA.
ACS Nano. 2008 Sep 23;2(9):1879-84. doi: 10.1021/nn800376x.
We study the optical and electrical properties of transparent conducting films made from length-sorted single-wall carbon nanotubes (SWCNT). Thin films of length-sorted SWCNTs, formed through filtration from a dispersing solvent onto a filter substrate ("buckypaper"), exhibit sharp changes in their optical properties and conductivity (sigma) with increasing SWCNT surface concentration. At a given surface concentration, tubes longer than 200 nm are found to form networks that are more transparent and conducting. We show that changes of sigma with SWCNT concentration can be quantitatively described by the generalized effective medium (GEM) theory. The scaling universal exponents describing the "percolation" transition from an insulating to a conducting state with increasing concentration are consistent with the two-dimensional (2D) percolation model. Shorter tubes and mixed length tubes form 3D networks. Furthermore, we demonstrate that the conductivity percolation threshold (x(c)) varies with the aspect ratio L as, x(c) approximately 1/L, a result that is also in accordance with the percolation theory. These findings provide a framework for engineering the optical and electrical properties of SWCNT networks for technological applications where flexibility, transparency, and conductivity are required.
我们研究了由按长度分类的单壁碳纳米管（SWCNT）制成的透明导电薄膜的光学和电学性质。通过从分散溶剂过滤到滤膜基底上形成的按长度分类的SWCNT薄膜（“巴基纸”），随着SWCNT表面浓度的增加，其光学性质和电导率（σ）会发生急剧变化。在给定的表面浓度下，发现长度超过200 nm的碳纳米管会形成更透明且导电的网络。我们表明，σ随SWCNT浓度的变化可以用广义有效介质（GEM）理论进行定量描述。描述随着浓度增加从绝缘态到导电态的“渗流”转变的标度通用指数与二维（2D）渗流模型一致。较短的碳纳米管和混合长度的碳纳米管形成三维网络。此外，我们证明了导电渗流阈值（x(c)）随纵横比L的变化关系为x(c)约为1/L，这一结果也符合渗流理论。这些发现为设计用于需要柔韧性、透明度和导电性的技术应用的SWCNT网络的光学和电学性质提供了一个框架。
