Using nitrile functional groups to replace amines for solution-deposited single-walled carbon nanotube network films.

Amine-terminated self-assembled monolayers (SAMs) can be utilized to selectively adsorb semiconducting single-walled carbon nanotubes (S-SWNTs), but are not ideal. Formation of these monolayer films from silanes can be dramatically influenced by atmospheric and other processing conditions, resulting in poor-quality SAMs or irreproducible results. The surface sorting method of fabricating these semiconducting nanotube networks (SWNTnts) can become ineffective if the functionalized surface is not smooth with high amine density. However, by replacing the amine with a nitrile group, SAM formation can be made more controllable and reproducible. Upon SWNT deposition, the nitrile group was found to not only adsorb higher density SWNTnts but also sort the nanotubes efficiently, as shown by micro-Raman spectroscopy. Upon testing these SWNTnts for device performance, these thin-film transistors (TFTs) were also found to yield higher quality devices than those fabricated on amine surfaces. Overall, these results expand the applicability of surface sorting and SWNT adsorption to other organic functionalities for nanotube separation. This report provides an outline of the merits and characterization of using the nitrile functional group for the separation and adsorption of SWNTs and its integration in network TFTs.

The effect of amine protonation on the electrical properties of spin-assembled single-walled carbon nanotube networks.

Amine-terminated self-assembled monolayers (SAMs) have been shown to selectively adsorb semiconducting single-walled carbon nanotubes (sc-SWNTs). Previous studies have shown that when deposited by spin coating, the resulting nanotube networks (SWNTnts) can be strongly influenced by the charge state of the amine (primary, secondary, and tertiary). When the amine surfaces were exposed to varying pH solutions, the conductivity and overall quality of the resulting fabricated networks were altered. Atomic force microscopy (AFM) topography had shown that the density of the SWNTnts was reduced as the amine protonation decreased, indicating that the electrostatic attraction between the SWNTs in solution and the surface influenced the adsorption. Simultaneously, µ-Raman analysis had suggested that when exposed to more basic conditions, the resulting networks were enhanced with sc-SWNTs. To directly confirm this enhancement, Ti/Pd contacts were deposited and devices were tested in air. Key device characteristics were found to match the enhancement trends previously observed by spectroscopy. For the primary and secondary amines, on/off current ratios were commensurate with the Raman trends in metallic contribution, while no trends were observed on the tertiary amine (due to weaker interactions). Finally, differing SWNT solution volumes were used to compensate for adsorption differences and yielded identical SWNTnt densities on the various pH-treated samples to eliminate the influence of network density. These results further the understanding of the amine-SWNT interaction during the spin coating process. Overall, we provide a convenient route to provide SWNT-based TFTs with highly tunable electronic charge transport through better understanding of the influence of these specific interactions.

Influence of electrostatic interactions on spin-assembled single-walled carbon nanotube networks on amine-functionalized surfaces.

Preferential interactions between self-assembled monolayers (SAMs) terminated with amine functional groups and single-walled carbon nanotubes (SWNTs) were exploited to produce nanotube networks (SWNTnts) via spin coating. We provide insight into the mechanisms of this system while simultaneously demonstrating a facile approach toward controllable arrays of SWNTnts. The chirality, density, and alignment of the SWNTnt was heavily influenced by adsorption onto amine-functionalized surfaces that were exposed to varying pH solutions, as evidenced by atomic force microscopy (AFM) and Raman spectroscopy. This pH treatment altered the charge density on the surface, allowing for the examination of the contribution from electrostatic interaction to SWNT adsorption and SWNTnt characteristics. Secondary and tertiary amines with methyl substitutions were utilized to confirm that adsorption and chirality specific adsorption is largely due to the nitrogen lone pair, not the neighboring hydrogen atoms. Thus, the nature of adsorption is predominantly electrostatic and not due to van der Waals forces or localized polarization on the SWNTs. Moreover, the overall density of SWNTnts is different for the various amines, indicating that the accessibility to the lone pair electrons on the nitrogen plays a crucial role in SWNT adsorption. With greater understanding of the amine-SWNT interaction, these findings can be utilized to control SWNTnt formation for the precise integration into electronic devices.

Solution assembly of organized carbon nanotube networks for thin-film transistors.

Ultrathin, transparent electronic materials consisting of solution-assembled nanomaterials that are directly integrated as thin-film transistors or conductive sheets may enable many new device structures. Applications ranging from disposable autonomous sensors to flexible, large-area displays and solar cells can dramatically expand the electronics market. With a practical, reliable method for controlling their electronic properties through solution assembly, submonolayer films of aligned single-walled carbon nanotubes (SWNTs) may provide a promising alternative for large-area, flexible electronics. Here, we report SWNT network TFTs (SWNTntTFTs) deposited from solution with controllable topology, on/off ratios averaging greater than 10(5), and an apparent mobility averaging 2 cm(2)/V.s, without any pre- or postprocessing steps. We employ a spin-assembly technique that results in chirality enrichment along with tunable alignment and density of the SWNTs by balancing the hydrodynamic force (spin rate) with the surface interaction force controlled by a chemically functionalized interface. This directed nanoscale assembly results in enriched semiconducting nanotubes yielding excellent TFT characteristics, which is corroborated with mu-Raman spectroscopy. Importantly, insight into the electronic properties of these SWNT networks as a function of topology is obtained.