Department of Chemical Engineering, Stanford University, Stanford, California 94395, USA.
ACS Appl Mater Interfaces. 2010 Sep;2(9):2672-8. doi: 10.1021/am1005223.
To facilitate solution deposition of single-walled carbon nanotubes (SWNTs) for integration into electronic devices they need to be purified and dispersed into solutions. The vigorous sonication process for preparing these dispersions leads to large variations in the length and defect density of SWNTs, affecting the resulting electronic properties. Understanding the effects of solution processing steps can have important implications in the design of SWNT films for electronic applications. Here, we alter the SWNTs by varying the sonication time, followed by deposition of sub-monolayer SWNT network films onto functionalized substrates. The corresponding electrical performance characteristics of the resulting field effect transistors (FETs) are correlated with SWNT network sorting and morphology. As sonication exposure increases, the SWNTs shorten, which not only affects electrical current by increasing the number of junctions but also presumably leads to more defects. The off current of the resulting transistors initially increased with sonication exposure, presumably due to less efficient sorting of semiconducting SWNTs as the defect density increases. After extended sonication, the on and off current decreased because of increased bundling and fewer percolation pathways. The final transistor properties are influenced by the nanotube solution concentration, density, alignment, and the selectivity of surface sorting of the SWNT networks. These results show that in addition to chirality, careful consideration of SWNT dispersion conditions that affect SWNT length, bundle diameter, and defect density is critical for optimal SWNT-FET performance and potentially other SWNT-based electronic devices.
为了促进单壁碳纳米管（SWNTs）的溶液沉积，以便将其集成到电子设备中，需要对其进行纯化并分散到溶液中。为了制备这些分散体，需要进行剧烈的超声处理，这会导致 SWNTs 的长度和缺陷密度发生很大变化，从而影响其电子性能。了解溶液处理步骤的影响对于设计用于电子应用的 SWNT 薄膜具有重要意义。在这里，我们通过改变超声时间来改变 SWNTs，然后将亚单层 SWNT 网络薄膜沉积到功能化基底上。所得场效应晶体管（FET）的相应电性能特征与 SWNT 网络分类和形态相关联。随着超声暴露的增加，SWNTs 变短，这不仅通过增加结的数量来影响电流，而且可能导致更多的缺陷。所得晶体管的关电流最初随着超声暴露的增加而增加，这可能是由于缺陷密度增加，半导体 SWNTs 的排序效率降低。经过长时间的超声处理后，导通和关断电流减小，因为 bundling 增加，且渗流途径减少。最终的晶体管性能受到纳米管溶液浓度、密度、对齐和 SWNT 网络表面排序选择性的影响。这些结果表明，除了手性之外，还需要仔细考虑影响 SWNT 长度、束直径和缺陷密度的 SWNT 分散条件，这对于优化 SWNT-FET 性能以及其他潜在的基于 SWNT 的电子设备至关重要。
