title: The effect of amine protonation on the electrical properties of spin-assembled single-walled carbon nanotube networks.
abstract: 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.
authors.affiliation: Department of Chemical Engineering, Stanford University, Stanford, CA 94305, USA.
authors.forename: Justin P
authors.initials: JP
authors.lastname: Opatkiewicz
authors.forename: Melburne C
authors.initials: MC
authors.lastname: LeMieux
authors.forename: Nishant P
authors.initials: NP
authors.lastname: Patil
authors.forename: Hai
authors.initials: H
authors.lastname: Wei
authors.forename: Subhasish
authors.initials: S
authors.lastname: Mitra
authors.forename: Zhenan
authors.initials: Z
authors.lastname: Bao